Author Topic: BSA C series OHV Engine Dismantle with pictures  (Read 5181 times)

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Online Cosmikdebriis

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BSA C series OHV Engine Dismantle with pictures
« on: October 06, 2014, 12:40:57 AM »
Still working on this old project but thought I'd compile it in to one thread. I'll edit it as time allows.

The following is a guide to the complete dismantling of a BSA C11g Engine.
The C series OHV engines are broadly similar so this can be used as a rough guide for other models including the C12.

The disclaimer. Please note this is just my personal take on how to dismantle the engine. Other methods are suitable. I can and will not accept any responsibility to damage caused howsoever to any persons or property who may choose to follow this guide in part or in full. You do so entirely at your own risk.

Before you Start
Some basic assumptions have been made as follows.
1.   The engine oil has been drained.
2.   The engine has been removed.
3.   The reader Has some mechanical aptitude commensurate for the task.
4.   The reader Has the required/appropriate tools for the task.

Some things you will need.
1.   A set of open ended  Whitworth spanners
2.   A set of Whitworth ring spanners
3.   Screwdrivers, pliers, hammer.
4.   A suitable container/box(s) for the parts.
5.   Plastic bags for keeping parts clean (old carrier bags are suitable).
6.   A notepad, masking tape and marker pen/Sharpie for labelling parts.
7.   Clean rag.

Specialist tools.
  • Valve spring compressor

Some things that will help.
1.   Circlip pliers
2.   Puller
3.   5mm Diameter steel rod of 75mm length.

General Advice.
Clean the externals of the engine before disassembly.
Immediately place parts such as the oil pump, piston etc in plastic bags to keep them clean.
Label parts an keep associated part together to aid reassembly.

Do’s and Don’ts
Don’t… hit anything with a hammer. Think first and try an alternative.
Don’t… use a screwdriver as a pry bar without considering the consequences.
Do… use a ring spanner in preference to an open ended spanner where possible.

2.  Remove the Cylinder head

2a. Undo and remove the retaining bolt A. then lift and remove the rocker box B. Note: some models (as in the picture) have an oil feed through this bolt. Others may have a standard headed bolt.

2b. Picture shows the rocker gear and valve springs with the rocker box removed.

2c. Flatten the ears of the elongated tab washer using an old screwdriver. You may need the judicious use of a hammer.

2d. Undo the two rocker spindle retaining bolts B. and lift off rocker spindle. Place in a plastic bag to keep clean.

2e. Remove the pushrods A. (2 off). Make a note of which push rod fitted where as it is advisable to replace them in the same place. Label them with masking tape and a pen. The top of the Exhaust pushrod points towards the front of the engine and the inlet towards the rear.

2f. Remove the cylinder head retaining nuts (and washers) A. There are seven of them around the barrel.

2g. Lift off the cylinder head. This may well be stuck and it is possible to pry the head off with an old screw driver provided you take the following precautions. The head and barrel are made of cast iron which is very brittle and will easily brake. NEVER use a hammer on cast iron. If you need to use a screwdriver to pry the head off ONLY use it where the seams caused in manufacture add strength (labelled B. in picture 2f). Be VERY careful.

2h. Cylinder Head removed. It is advisable to replace the nuts and washers on the studs at this time to keep them safe and also to protect the ends of the threads.

3. Removal of the Cylinder Barrel.

3a. Undo the six barrel retaining nuts (A). and washers.

3b. Loosen or remove the two nuts (A). as this may help in removing the barrel. It may be helpful to loosen the other nuts around the crank cases at this time.

3c. Push the piston to the bottom of the stroke with your hand and lift off the barrel making sure the piston does not get caught, twisted or allowed to fall onto the sides of the crank case studs etc. The Barrel may be stuck and need a little persuasion with the palm of the hand. DO NOT use a hammer. It is advisable to place some clean rag in the crank case mouth under the base of the piston as you lift the barrel. This will stop the piston from being damaged and stop the ingress of muck into the crank cases.

3d. If you do not intend to remove the piston at this time (see chapter 6) Then wrap the piston in rag to protect it.

4. Remove the points assembly.

4a. Remove the two points cover retaining screws (A). Note: that part (B). is a non-standard part and as such may not exist on your engine.

4b. Undo the two points backplate retaining screws (A). and lift out the assembly complete. Replace the screws and washers in the housing for safe keeping.

4c. Undo and remove the centre bolt (A) which retains the advance retard mechanism. This mechanism is a taper fit in to the cam shaft assembly and may need a special tool to remove. You should be able to easily make your own tool.

METHOD 1. with special tool.

4d. You will need a long bolt with a 5/16” Bscy thread. A 5mm diameter steel rod of 75mm length. It is possible to fabricate the rod from an old drill bit but make sure you grind the ends flat. DO NOT try and use a rod of more than 5mm diameter as you may damage internal threads in the cam shaft.


4e. Insert the rod (A). fully in to the advance retard mechanism. It should fit right in to the mechanism. If it does not and stands proud of the mechanism then either your rod is too thick (more than 5mm dia), too long (more than 75mm) or there is some other damage.

4f. Screw the bolt in to the top threaded part of the advance retard mechanism. This should push down on the rod and lift the mechanism from the taper. Note: It may go with a bit of a clunk.

METHOD 2 Without special tool

It is preferable to use method 1 but under some circumstances it may be necesarry to use the method below.

You will need the same bolt as in the above method but also a large penny washer. A small block of wood and a sturdy spanner.

4g Insert the bolt as above but with the addition of the penny washer. Place the block of wood over the casing then, using the wood as a fulcrum and the spanner as a lever. Give the spanner a sharp blow with the palm of the hand to loosen the mechanism from the taper.

NEED TO TAKE A PICTURE FOR THIS. (not actually tried this as yet but will do and see how it goes) ;) So... If you are reading this with a view to trying it. Be VERY careful.

4h Withdraw the advance retard mechanism complete, check for wear of the component parts. Renovation of the mechanism is beyond the scope of this article.

5.Remove the Camshaft.

5a. Remove the timing cover.

Undo the six retaining screws and lift off the timing cover. You may need to give it a bit of a thump and wiggle with the palm of your hand as it is located by studs. Bo not be tempted to pry off the cover with a screwdriver as you will almost inevitably and up with a damaged part and a resulting oil leak.

5b. Timing cover removed.

5c. Lift out the cam shaft
You may need to spread the (lower) rocker arms to allow the cam lobes to pass them.

5d. Remove the cam rockers Method 1
There are two methods of removing the cam rockers.
Method 1 Remove circlip (arrowed) and slide contents from rocker shaft.
Method 2 Leave circlip in situ and slide the rocker spindle, complete with rockers and associated components, directly from the case. This should be a tight fit in the case so do not be surprised if you end up resorting to method 1. There is no real need to remove the spindle unless it is showing signs of wear.

5f Cam rocker assembly removed.
Make a note of positioning of all components, especially washers to aid reassembly. Place complete assembly in a plastic bag to keep clean.
Parts Described...
A Thrust washer (not shown on BSA parts list).
B Cam Rockers. Note the inside one, nearest the the crank shaft, is the exhaust rocker the associated pushrod pointing towards the front of the engine. Part No 29-2285 (both are the same).
C Spacer. Part No 29-2171
D Circlip. Part No 29-2170
E Shaft. Part No 29-1994

Chapter 6 Remove and check Piston.

6a Remove circlips
There are two types of circlips commonly used to retain the gudgeon pin. In the diagram the circlips have ears that allow the use of circlip pliers to remove them. Alternatively you may have plain wire clips in which case you will need to pry them out with a suitable implement. Take care not to damage the piston.
Circlips should always be discarded and replaced with new ones.

Method 1

6b Drift out gudgeon pin.
It is possible to drift out the gudgeon pin from the piston but you must take extreme care if you choose this method.
You will need a suitable drift, such as an old bolt, and a hammer.
Insert the drift in to the gudgeon pin Ihe inside of the gudgeon pin is usually tapered so choose a drift that fits just in to the pin. Make sure you use one hand to support the other side of the piston to absorb the shock and avoid damaging the con rod. then use a hammer to remove the pin. You do not need to completely remove the pin and approx two thirds out is enough to remove the piston.

Method 2

6d Using a draw bolt to remove gudgeon pin

Need to take pictures etc...

6e Piston removed.

cleaning and inspection of piston.

General. Inspect the piston for obvious signs of damage such as cracks or severe grazing of the skirt. Should you discover either of the above the piston must be discarded and replaced. In this case you may need to purchase an oversize piston and have the barrel bored to accept the new piston.

6e clean piston crown.
The crown of the piston will gradually build up a thick layer of carbon deposits which will need to be removed. Judicious use a wire wheel is best. Try to avoid using sharp objects such as a screwdriver or knife or you may damage the surface of the piston.
When the piston crown is clean it should reveal information on the size of the piston (A).  I will explain more on this later.

6f Examine piston skirt.
Examine the piston skirt for signs of damage. some minor grooving is acceptable but deep grooves will mean the piston will have to be discarded. The piston in the picture is acceptable.

6g Remove the piston rings...
Great care should be taken when doing this as the piston rings are very fragile. Start with the ring at the top of the piston and as they are removed make sure  you know which one goes where and which way up it is fitted. you need to replace the rings in the same place and orientation as you remove them.
Using your thumb nails gently spread the rings at the ring gap till they are just loose enough to clear the piston. Lift and remove. This can take practice but don't be tempted to spread the rings too far or they will certainly break.

Picture needed

6h Use an old ring to clean ring grooves.
some carbon may have built up in the ring grooves in which case you can use an old ring to clean the groove. Be careful not to dig in to or otherwise damage the piston.

6j Check the gudgeon pin and small end bush.
Visually inspect the gudgeon pin for signs of wear. If there are ridges in the centre portion then the pin will have to be discarded. Inspect the small end bush for signs of wear then insert the gudgeon pin back in to the bush. It should slide in and rotate fairly easily. if you need to hammer the pin in then there are problems that need further investigation. Next, with the pin positioned centrally in the bush try and rock the ends (see picture). there should be or no appreciable movement. if you can feel the pin rock and the gudgeon pin is in good condition then the small end bush will need replacing. This is beyond the scope of this article.

6k Inspect bore wear 1
The top of the bore may have some build up of carbon. You will need to remove this first. use a brass brush to clean back to bare metal.
First check is visual. Look for signs of a lip at the top of the bore. This will normally be most pronounced on the front edge of the bore. It may help to run your finger up the bore to feel for any ridges. Should there be a pronounced ridge then you will probably need a new piston and re bore. Re boring is a specialist operation and you will need to find a competent engineering firm to undertake this.
Another check but without specialist measuring equipment is to measure bore wear by using a piston ring. Insert the top piston ring in to the top of the bore

6k Inspect bore wear 2
Assuming the piston does not have any rings on it. Invert the piston and use it to push the ring down the bore. You will need to push the ring about 1cm down the bore as this is where maximum wear occurs.

6k Inspect bore wear 3
Remove the piston to reveal the ring. Using feeler gauges check the ring gap (arrowed) and compare this with manufacturers specifications.  The ring gap must be measured with the ring square in the barrel so if you move the ring you will need to start from the beginning.

Should the ring be outside specification but the bore not have a ridge then you may only need a new piston (of the same size). Should the ring be outside of specification and there is an appreciable ridge then you will probably need a re bore. Pistons are generally available in three over sizes +020" +040" and +060" (thousandths of an inch). Look at the piston crown to decide if a re bore is possible. If in doubt, contact a competent engineer.

Chapter 7.

Removing the oil pump.

7a. Remove the Timing Pinion.

The timing pinion retaining nut should should be held from shaking loose by a tab washer (missing on this engine). you will need to bend down the tab as previous chapter.

The nut has a normal RH thread but you will need to stop the crankshaft from rotating in order to undo it.

Method 1.

Lock the crankshaft with rod through the small end.
You will need to small blocks of wood and a rod to put through the small end. It is usually possible to use the original gudgeon pin.
Rotate the crank shaft anti clockwise till the rod locks on the wood. Undo the nut. DO NOT use a rod of small diameter or you may damage the small end bush and possibly the conrod eye.

Method two.

Picture Needed...

You will need a block of wood of suitable size. Place the block of wood in to the crank case mouth to lock the big end from rotating.
Undo the nut.

Remove the oil pump driving retaining pin.

The oil pump drive shaft is held in place by a retaining pin. BSA Part No. 65-2603. on the outside of the pin there may also be a washer/spacer. If fitted pry out the washer. The pin may simply come loose but if not you will need a 3/16" BSCY threaded bolt, penny washer and suitable spanner.
Screw the bolt and washer in to the pin then, using the end of the crank shaft as a fulcrum, lever out the pin.

Drive pin removed

Remove sump plate
To gain access to  the oil pump main body we need to remove the sump plate.
Unscrew the four bolts and spring washers (arrowed) and lift off the plate. It may well be stuck tight by gasket sealant in which case you may need to lever it off. If so be very careful not to damage anything or you will inevitably end up with an oil leak.

Sump Plate removed
Note the dirty oil collected in the bottom of the sump plate, Make sure this is thoroughly cleaned before replacing. Rub some of the oil between your fingers. If you get a gritty feeling then this may be a sign of problems elsewhere in the engine.

Remove the filter
As with the sump plate the filter may need to be prized off. again be very careful not to bend the filter. Check the top part of the filter (A) for larger pieces of metal. Should you find any then it is likely there is some serious damage to the engine. Note the oil pump body (B)

Remove the oil pump body.
Undo the two retaining bolts (A) Note that in this engine one of the bolts has previously been replaced by an allen bolt. DO NOT undo the two smaller bolts as these hold the pump body together.

Lift out the complete pump body
The pump should lift out fairly easily. It is possible the drive spindle may come with it, otherwise you will need to remove it later.

Pump Body removed...
With the body removed visually inspect the drive (need to arrow drawing) for signs of wear. Next rotate the drive by hand. It should turn freely in both directions and you should see oil being sucked in to one side of the pump and expelled from the other.
Should the oil you have previously tested in the sump be clear from grittyness.  The drive be undamaged and the pump rotate freely then do not disassemble any further. Place the pump in a plastic bag immediately to stop the ingress of dirt and general muck.

Remove drive spindle.
Push the drive spindle, BSA part No 65-2602 from the crank case. It should move freely. If not then there is likely a serious problem within the engine

Drive Spindle removed
Visually inspect the shaft and drive gear for signs of wear. The spindle cannot be repaired so if there is any damage, you will need to replace it.

Remove timing pinion
With the pump drive spindle removed you now have access to fit a suitable puller to the timing pinion. This will normally need to be drawn from the crank shaft as it should be a tight fit. For this you will need a puller (see picture).
Place the puller over the pinion and screw down on the end of the shaft to draw off the pinion. Make sure to pull from the larger diameter gear so as not to damage the oil pump drive gear.

Pinion Removed...

Remove Woodruff Key.
Do not forget to remove the woodruff key (arrowed), (BSA part No 15-50). Place it together with the other oil pump parts in a plastic bag for safe keeping.

Remove oil pressure release valve.
Unscrew the oil relief valve retaining bolt (BSA part No 65-2188). Be careful not to loose the internal spring and ball bearing.

Components of oil pressure release valve
A BSA Part No 65-2188
B Fibre/copper washer
C BSA Part No 66-1682
D Ball Bearing 3/16"
Visually inspect and thoroughly clean all parts. Keep together and clean in a plastic bag.

Chapter 8 Remove the Crank Shaft

8a Undo the retaining studs.
If not done previously then undo and remove the remaining nuts and/or studs around the perimeter of the crank cases.

8b Remove the Engine Breather collar.
You should be able to simply pull the engine breather collar (BSA part No 29-2027) from the shaft. Make a note of orientation, holes towards the inside of the engine, nearest the flywheels. Visually inspect for signs of damage. if the engine has been stood for some time then corrosion may have damaged the outside faces of the collar which will in turn damage the oil seal and cause oil leaks. The collar will therefore have to be repaired or replaced. You should find a small tab on the inside of the collar which locates on the splines on the crankshaft. This stops the collar from rotating on the crankshaft and without this tab the breather system will not work. Make sure the row of holes in the collar are not blocked as these allow the engine to release crank case pressure reducing oil leaks.

8c Split the crank cases.
It is likely that the crank cases have been previously joined together with gasket sealant. This will make the cases quite difficult to get apart.
In this instance I use a small chisel/old screw driver to pry the cases apart. However this MUST bed done with extreme caution and ONLY in certain areas. Failure to adhere strictly to the following will very likely cause damage to the cases and inevitable oil leaks.
The ONLY place it is safe to use a chisel is on the outside of the main mounting bosses of the cases (see picture) Insert a chisel in to the join and tap with a hammer. As one side opens, move to the opposing side and repeat. Do not under any circumstances let the end of the chisel/screwdriver go past the bolt hole to the inner surfaces. If you are unsure then simply insert an old bolt in to the hole before you start and this should prevent your tool from going to far. Gradually work the cases apart. You may find inserting a thicker piece of metal such as a tyre lever helps. Eventually you will be able to get your fingers in and with a bit of wiggling the cases should separate.
After you have done this you must inspect the edges of the mountings that you have used to pry the cases apart and dress any marks with a file. Failure to do this may stop the cases joining properly and result in an oil leak.

8d Timing side crank case removed

8e Drive side crank case removed

8f Remove main bearing retaining clip.
The drive side main bearing (BSA Part No 24-732) Bearing number 6305 is held in the cases by a large cirlclip (BSA Part No 66-1701) You will need to pry the clip out with a screwdriver or similar. Make sure you do not damage the crank case.

8g Heat the crank case to aid bearing removal.
It is certainly advisable to change the main bearing at this time, even if it is not showing obvious signs of wear. This is a relatively cheap item and can be purchased from most bearing suppliers. I recommend you use a good quality bearing as the minor added expense is more than justified by the problems caused by the potential bearing failure of a cheap one.
Use a paint stripper gun to warm the cases. Do it evenly and try and get the case to a temperature where water will boil (spitting on the case is the approved test). As the aluminium of the case expands more than the steel of the bearing the bearing will become relatively loose. In some circumstances the bearing may well simply fall out otherwise you will need to drift it out with a suitable drift.

8h Using a drift to remove the bearing.
An old socket of suitable size will often do. Add an extension and make sure you do not slip and hammer the cases. In the unlikely event that this does not work you may need to get the cases even hotter in which case a blow lamp, kitchen oven or gas ring is ideal (assuming you can get away with it).
Obviously you should wear gloves at all times to avoid burning yourself on the hot metal.

8j Remove the oil retaining washer.
Between the bearing and the case you should find an oil retaining washer (BSA Part No 24-2112) This should be slightly concave. Make a note of which way round is is fitted and visually inspect for damage. Ideally you should replace this washer as a matter of course.

8k Remove the drive side oil seal.
The drive side oil seal (BSA Part No 29-1970) should be removed, discarded and replaced with a new one. The seal can be readily obtained from most bearing suppliers. Size being...
Inside Diameter 33.27mm 1.310"
Outside Diameter 47.5mm 1.870"
Width 6.35mm 0.250"
Place a suitable block of wood on the crank case then gently lever the seal out with a screw driver. It is best to do this whilst the case is still hot. Again be very careful not to damage the case.
Picture needs changing

8l Check breather hole
Insert a bit of wire in to the breather hole to make sure the passage is clear. Should this be blocked then pressure will build up in the engine and cause oil leaks. (note in this picture the oil seal is still in place. normally this would have already been removed).

Chapter 9. Remove the valves...

9a Remove the studs.
A good method of removing studs is to lock two nuts together (A) on the same thread and then undo the bottom nut. This should lock against the top nut and unscrew the stud. Screw the first nut to the bottom of the thread so that it is just finger tight. screw another nut down on top of the first nut then, using two spanners, tighten the nuts together. Next, with a spanner on the bottom nut only, unscrew the nut which should unscrew the stud. After removal separate the two nuts and remove. Clean the studs with a wire wheel and visually inspect the threads for damage. In order for the stud to do its job properly the nut shoud freely run up and down the entire length of the thread.
If the stud is particularly difficult to remove then try using a releasing agent and or some heat. It may also help to place the head upside down on the bench, hold a piece of hard wood over the end of the stud and give a sharp tap with a hammer to shock the threads loose. Be careful as the head is made of cast Iron which is very brittle.

9b Using a Valve Spring Compressor i
The only practical method of removing the valves is with a special tool called a valve spring compressor. They come in various shapes and sizes but you will need one for an OHV (Over Head Valve) engine.

9c Using a Valve Spring Compressor ii
Place one end of the tool over the Valve Spring Collar (BSA Part No 31-111). Make sure it fits centrally over the collar.

9d Using a Valve Spring Compressor iii
Place the other end of the tool over the centre of the valve head.

9e Using a Valve Spring Compressor iv
Depending on how your compressor is constructed you will usually screw one and/or other end in to compress the valve spring. Do this slowly as you shouldn't need too much force to release the collar. Should it prove difficult to turn and there is no sign of the collar moving then give a light tap with a hammer to the collar end of the compressor tool. Be carefull though as the whole setup is spring loaded and bits can fly out and easily get lost.
Wind the valve collar slowly down the valve stem. You do not need to fully depress the spring to remove the collar though. after a few turns you should be able to see two collets (A) (BSA Part No 29-410) that secure the collar to the valve stem. You will need to pry these out with a screwdriver or similar. This can be quite a fiddly job. Sometimes a magnet will help.

9f Remove the valve springs.
After you have removed the collets you can unscrew the valve spring compressor and remove the valve collar and the two valve springs (BSA Part No 31-108) Ideally the springs should be replaced and can be bought in sets.
Do the same for both valves.

9g Showing valve guide and spring cup
With the valve springs removed you should be able to see the valve guide (BSA Part No 65-37) and the  Spring cup (A) (BSA Part No 15-1215)
The cup is held in place by the guide and cannot be removed at this time.

9h Remove the valve i
Push the valve from the spring end down until the end just about disappears down the valve guide (see pic). Check that it will slide freely in to the valve guide. If not check for ridges around where the collets sat. Should you find any damage hear then you must replace the valve. If you choose to try and repair this damage then you run the risk of the valve coming loose when the engine is running and dropping in to the cylinder with catastrophic results.

9j Check for wear and remove valve.
This is a good time to check for wear to the valve and/or guide. With the head of the valve just slightly raised (see pic) try and wiggle the valve sideways. There should be very little or no play. Should the valve rock from side to side then the valve and guide will almost certainly need replacing.
Withdraw the valve completely and check the stem for signs of wear. If you can feel ridges just below where the collet groove is then the valve will need to be replaced. Also check to see if the valve is bent. Even a very slight bend is too much and the valve will need to be replaced. Do the same for both valves. The valves are different but the springs, collars, cups, collets and guides are the same.
It is advisable to renew the valves but if there is no wear then it may not be necessary.

9k Remove valve guides i
Accompanying picture shows the two valve guides (A) You will need to drift them out from this side.

9l Remove valve guides ii
You will need a special drift to remove the guides though this can be made from an old bolt. The accompanying picture shows the home made drift. The diameters listed are critical though the length of A can be longer.
A Length:100mm (approx)  Diameter: 12-13mm
B Length: 20-30mm Diameter 7mm (exactly).

9l Remove valve guides iii
Place the cylinder head uptuned on the bench. Preferably place a block of wood on the bench under the head. Next place some more wood on the face of the head to protect the head from damage by the hammer. Note, for clarity the wood is not shown in the picture. Drift out the guide using the hammer and drift. The guide will eventually stop moving as the end will hit the wood/bench. You will then need to arrange some small pieces of wood to raise the head but allow the guide to drop. Be very carefull as the guide ia about to fall not to damage anything with the hammer.
Note. As standard the valve guides are made of cast iron and may well break up on removal. If so you will need to persevere until the entire guide is removed.

9m Valve guide and spring cap removed
Showing valve guide (A) and spring cap (B)removed.
Cast iron valve guides MUST be replaced once removed.

9 Clean and inspect cylinder head.
The compression chamber, valve seats and ports will almost certainly be coated with thick carbon deposits. you will need to clean this off before you can inspect for damage. Do not be tempted to try and scrape this off with a screwdriver or similar as you may well cause irreparable damage. Ideally degrease the head with a suitable degreasant and the leave the head complete in a strong caustic soda bath for 24hours. You can also place the valves and any other iron components in the same solution for cleaning.
Be very careful when using caustic soda as it can burn exposed skin. Also do not try and clean non ferrous metals such as aluminium or they will likely dissolve. Note that the caustic solution will almost certainly remove paint. Remove the components from the solution (using rubber gloves) and check for wear/damage.
« Last Edit: October 08, 2014, 09:02:23 AM by Cosmikdebriis »
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