Author Topic: Tight engine  (Read 2155 times)

0 Members and 1 Guest are viewing this topic.

Online camman3

  • Moderator
  • Gold Member
  • ****
  • Posts: 6612
  • Country: gb
  • The more I know, the less I understand......in UK
Re: Tight engine
« Reply #90 on: February 18, 2018, 02:19:45 PM »
Or bring it to my place, Cosmic, and anybody else for that matter, can come over and help, and your wife, children, dog and granny, can walk to the beach from here while we set too, and put this bike right once and for all ;D
Graham
1957 C12
In sunny (sometimes) Christchurch, Dorset, UK

Online Pete

  • Administrator
  • Silver Member
  • ****
  • Posts: 2094
  • Country: gb
  • Location: Kennet & Avon Canal
Re: Tight engine
« Reply #91 on: February 18, 2018, 02:34:21 PM »
That's a good offer Chris. Do you have a means of transporting it?
1948 BSA C11
1932/56 C12Rudge
N.B. Andromeda
Volvo V40

Online Cosmikdebriis

  • Moderator
  • Gold Member
  • ****
  • Posts: 5501
  • Country: pg
Re: Tight engine
« Reply #92 on: February 18, 2018, 05:33:42 PM »
OVERVIEW.

The primary chain connects the engine to the clutch which in turn connects to the gearbox that drives the gear box sprocket that turns the rear drive chain to the back wheel.

Primary chain tension on a pre-unit BSA is accomplished by moving the gearbox backwards and forwards, towards and away from the engine. The gearbox is held in place by two bolts underneath the main casing. and these locate in slots in the engine/gearbox plates allowing for adjustment.

The bolts are a specialist part (see parts list) and have two special locking "washers" that crimp against the gearbox/engine plates to keep the gearbox from moving when tightened.

It is very important that the threads on both the bolts and associated nuts are in clean and good condition to be able to transmit the pressure required to hold the gearbox securely.

There are two basic potential issues here if the bolts/washers are not doing their job properly...

There are two opposing forces trying to move the gearbox when in use.
Firstly, the primary chain will try and drag the gearbox forward (towards the engine). There are two main effects from this.
A) the primary chain will become loose and can cause damage.
B) (and often less considered) if the gearbox moves forward it will also tighten the rear/drive chain (to the back wheel) which can add to wear on the rear chain and sprockets.
Alternatively and oppositely.
A badly adjusted rear/drive chain that is too tight will try and drag the gearbox backwards and can cause the primary chain to go too tight and break/cause damage.

For both reasons above it is imperative the gearbox is held tightly when the chain(s) are adjusted properly.

ADJUSTMENT

it is advisable to loosen the rear chain before adjusting the primary chain, then adjusting the rear chain AFTER the gearbox is secured (properly).

Loosen the gearbox retaining bolts (making sure all the relevant parts are there and in the right place (see parts lists).

Move the gearbox as far forwards as possible but pushing wedging or any suitable means.
Fit the primary chain making sure the split link is fitted with the  Closed end facing the direction of travel.
Next a bit of a cheat. Assuming the rear chain is fitted, pulling downwards on the bottom of the rear chain will drag the gearbox backwards. Alternatively wedge the gearbox by other means.
DO NOT tighten anything at this stage.
The primary chain should now be fitted and ready to turn the engine over (by hand with a spanner).
What we are trying to achieve is a chain that is not bowstring tight but also not loose enough to touch the outer casing.
Due to manufacturing tolerances, it is highly unlikely the chain will have the same taughtness throughout a revolution of the engine.
It is therefore best to find the tightest point during rotation and use that as our datum.
To do this rotate the engine slowly with a spanner whist checking the taughtness of the primary chain.
It should be noted that in normal use the engine will pull the top run of the chain tight and the bottom run of the chain is where you should measure the slack. That is assuming you are turning the engine over in an anti clockwise direction. It is also worth mentioning that, due to the tension in the valve springs, the engine may not turn over smoothly so you will need to keep a good grip on the spanner.
Do this for a few revolutions until you are sure you know where the tight spot is.
When you have found the tight spot, adjust the gearbox so that there is just 2mm of travel up and down.
Tighten the gearbox retaining bolts and rotate the engine a few more times checking that the chain still has only 2mm play at its tightest point.
You may find tightening the bolts will move the gearbox and adjust the chain tension so it is imperative you check this after tightening the bolts.
You will probably need to adjust this several times before you get it right.
Once you are satisfied rotate the engine again and find the slackest spot, make sure this does not allow the chain to touch the primary chain case.
If the chain does touch the primary chain case whilst only having 2mm of travel at it's tightest, then you have a problem that is beyond the scope of this article.
Assuming the chain is now correctly adjusted, adjust and tighten the rear chain according to the specification (not in the scope of this article).
With all chains adjusted, turn the engine over one more time to check everything is okay.
Do not yet re fit the primary chain case but take the bike for a short run including some hard accelerating and braking.
Check if the primary chain tension is still correct and, if so, re fit all parts and go for a longer ride.
Before you go, make a note of the rear chain tension. If when you return, the rear chain is either tighter or looser the gearbox will likely have moved. and you need to check the special bolts holding the gearbox in place are doing their job. (beyond the scope of this article).

NOTES.

It is not a good idea to fit new chain on old/worn sprockets. However, on vintage machinery it is not always practical or indeed possible to replace sprockets but this will cause the chain to wear out more quickly.

A new chain, especially on old/worn sprockets will stretch under first use so it is important to check primary chain tension regularly after replacing for at least the first hundred or so miles of use. After that things will normally settle down and the chain should be checked at less regular intervals.

It is a good idea to check the sprockets for signs of wear on the sides. If one side of a sprocket is showing wear (often shiny) but the other side is dull then the chances are the other sprocket will show wear on the other side. This is a clear sign the sprockets are not in line and this must be investigated and repaired before further use.

A quick method of measuring chain wear is to lay the chain on a flat surface so that the rivets in the links are horizontal. Then try and bend an arc in the chain (in the direction it is not meant to bend).
Unfortunately it does take a trained eye to fully appreciate exactly how much of a curve you should be able to produce as this can depend on chain type to some degree but a good chain should not bend very much at all.
« Last Edit: February 19, 2018, 12:20:38 AM by Cosmikdebriis »
A bike on the road... Is worth two in the shed...

Online camman3

  • Moderator
  • Gold Member
  • ****
  • Posts: 6612
  • Country: gb
  • The more I know, the less I understand......in UK
Re: Tight engine
« Reply #93 on: February 18, 2018, 05:52:21 PM »
Yes....then we can all go for a walk on the beach :)
« Last Edit: February 18, 2018, 05:56:45 PM by camman3 »
1957 C12
In sunny (sometimes) Christchurch, Dorset, UK

Online chaterlea25

  • Silver Member
  • ***
  • Posts: 2388
  • Country: ie
  • nr Cork Rep of Ireland
  • Location: Nr. Cork
Re: Tight engine
« Reply #94 on: February 18, 2018, 05:57:20 PM »
Hi Chris and All

It looks like the primary chain was tearing against the inner alternator alloy case?
Is the sprocket fitted the correct way round?
Check the sprockets for alignment before you reassemble
Make sure the spacer between the inner primary case and engine plates is fitted

I once made the mistake of fitting a primary chain from a bearing stockist, it shed all its rollers which then stuck to the rotor and chewed up everything in sight  ::)
So fit a good quality replacement

John

Offline cadetchris

  • Full Member
  • *
  • Posts: 151
  • Country: england
  • Location: Bristol
Re: Tight engine
« Reply #95 on: February 18, 2018, 07:39:46 PM »
lots of replies, so ill try my best to answer them.
starting with the most recent,
there is a lot of scuffing to the aluminium case for the alternator. I to thought i had the sprocket the wrong way around, but having checked the parts book it shows flat side to the engine, which mine has. It is missing part 82a which is marked as "alternator spinner". It didn't have one when i got the bike, so i assumed this was one of those bits people simply take off at some point within the bikes life and then continued on. Very much like spring washers or such like.
Would this bring the chain that tad bit further forward and prevent the scuffing? Again i assumed that the scuffing was the result of the chain going.

Its a very good offer and i am sorely tempted to take camman3's offer up. I am however lacking transport for the bike and lifting it into the back go my jeep would do me and the jeep in.

there is a lot of swarf in the case, but again to me it appears to be from the chain going and the chain potentially catching on the alternator case.
The clutch doesn't have any end play on it, its quite tight. The split washer is in place and held with grease whilst it was being assembled.

The joining link was on the right way and on right, someone mentioned to liken it to a fish swimming against the current, so curved end in the direction of travel.
I do think the chain was too tight. when i was turning around at the bottom of the road, i did open the throttle to give it a bit of wellie and that just taxed it too much and it broke at the weakest part. that being the joining link.

As for the case looking dry, it had some oil in it, but not a huge amount, probably about 150ml. Having asked the question of oil or no oil in the chain case, the amount and contrasting opinions i got was tbh quite confusing. Some said oil, some said no oil at all, some said oil the chain through the filler, some said it was designed to have oil in it, so oil goes in but use something like power steering oil as its light and not too thick.
So to a newbie (with this bike, but not mechanics in general) i deduced that oil was good but i hadn't put a huge amount in, partially due to me adding this 150ml to check the oil tightness of the case seal (it wasn't that oil tight it appeared) and i hadn't filled it up to the specified level as this was a sort of shake down ride.

Online camman3

  • Moderator
  • Gold Member
  • ****
  • Posts: 6612
  • Country: gb
  • The more I know, the less I understand......in UK
Re: Tight engine
« Reply #96 on: February 18, 2018, 08:32:50 PM »
Ok, so probably just chain too tight or the gearbox loose/twisted.

Sprocket is definately right way round....as far as oil is concerned and the varying opinions, they are all right, as long a the chain gets lubricated from time to time, just like the rear chain.....yes I know the primary runs faster than the rear so is more important, but on the other hand it is running in a cleaner drier environment.

I would get a new chain and set it up as per Daves (Cosmicdbris) excellent guide/explanation and see where you stand
Graham
1957 C12
In sunny (sometimes) Christchurch, Dorset, UK

Online Owen

  • Administrator
  • Gold Member
  • ****
  • Posts: 6648
  • Country: england
  • Solutions not problems
Re: Tight engine
« Reply #97 on: February 19, 2018, 07:18:28 AM »
Is the sprocket aligned to the clutch basket as that would cause the scuffing?
1940 C12 (350cc)
1945 C10 & C11
1953 C10 & C11
Most of a B20/3 in need of a lot of tlc

Offline cadetchris

  • Full Member
  • *
  • Posts: 151
  • Country: england
  • Location: Bristol
Re: Tight engine
« Reply #98 on: February 19, 2018, 09:13:47 AM »
Well that’s the new chain ordered and should be here on Wednesday.
I am going to check alignment between clutch and engine sprockets and if it’s not true or at least trueish, what shall I do? Thicker gasket between the rear chain cover and engine or maybe a washer?

Online Tman

  • Bronze Member
  • **
  • Posts: 1872
  • Country: england
Re: Tight engine
« Reply #99 on: February 19, 2018, 09:22:10 AM »
I would say try some sort of shim or spacer behind the engine sprocket if that's possible.
Spacing out the cover is curing the symptoms not the fault.

Online Cosmikdebriis

  • Moderator
  • Gold Member
  • ****
  • Posts: 5501
  • Country: pg
Re: Tight engine
« Reply #100 on: February 19, 2018, 09:24:41 AM »
if it’s not true or at least trueish, what shall I do?

If it isn't true then it's because you have a problem somewhere and, ideally, that should be investigated before trying any sort of "bodge" fix.

Let's hope it is true as, if not that opens up a whole new can of worms that could require some pretty extensive work.

Fingers crossed.

Out of interest. if you lay your old chain on top of the sprockets, keep it tight and look down the line, it should be fairly obvious. Also, look for wear on the sprockets as suggested  on the "Notes" section of my (rather lengthy) post above.
A bike on the road... Is worth two in the shed...

Online Owen

  • Administrator
  • Gold Member
  • ****
  • Posts: 6648
  • Country: england
  • Solutions not problems
Re: Tight engine
« Reply #101 on: February 19, 2018, 07:43:58 PM »
Try a 12" ruler across from the sprocket (without the alternator stator) if the engine sprocket needs spacing out you could always make a longer bush behind it?
1940 C12 (350cc)
1945 C10 & C11
1953 C10 & C11
Most of a B20/3 in need of a lot of tlc

Offline timsdad

  • Gold Member
  • ****
  • Posts: 6474
  • Country: england
Re: Tight engine
« Reply #102 on: February 20, 2018, 08:12:33 AM »
Yes, I always run a straight-edge down the sides. Anything will do - steel ruler, bit of alloy bar or whatever. It pays to check and it's more likely to discover that the gearbox is on the piss rather than out of alignment. If the sprockets are not straight then it needs looking at but I'd wager that the problem was just a cheap and nasty industrial chain that couldn't stand being a bit too tight. A good chain would have just destroyed the gearbox bearings in about a thousand miles.

These bits of chain that are bought from dealers are usually cut off long lengths of imported industrial stuff from the Orient or Eastern Europe and it's not fit for purpose on motorcycles. I either get decent branded chains, DID is my first choice, or something from Andy the Chain Man. Even Renolds haven't made any decent bike chain for many years - it's ok for occasional use on a C11 but I'd never put it on my old 650 Thunderbird or 250 Yamaha.


Ray
Just a motorcyclist.

Online MilitaryRon

  • Moderator
  • Silver Member
  • ****
  • Posts: 4714
  • Country: gb
  • Branksome, in Poole, Dorset UK
Re: Tight engine
« Reply #103 on: February 20, 2018, 08:46:57 AM »
I buy all my chains from John and Jane http://www.sprocketsunlimited.com/ What they don't know about chains is not worth knowing and a friendly couple you couldn't wish for. Ron

Online camman3

  • Moderator
  • Gold Member
  • ****
  • Posts: 6612
  • Country: gb
  • The more I know, the less I understand......in UK
Re: Tight engine
« Reply #104 on: February 20, 2018, 01:23:09 PM »
Like Ray, I would lay odds that it is just a case of cheap chain, too tight, snapping, and any misalignment down to the gearbox being "skewed". The sprocket is definately on the right way round, and as Dave says should not need longer bush or shims, as it is where it should be and the fault is elsewhere (if in fact there is one)......provided of course, you have the correct unmolested breather collar fitted behind front sprocket?
Graham
1957 C12
In sunny (sometimes) Christchurch, Dorset, UK