BSA C10 C11 C12

BSA C10 C11 C12 Forum => Technical Section => Topic started by: AdminPete on November 30, 2008, 11:48:32 am

Title: C11 top end overhaul
Post by: AdminPete on November 30, 2008, 11:48:32 am
From: Birchy  (Original Message) Sent: 06/01/2008 05:28
G,day all
hope you can help
Had a lot of noise from the top end of my C11 BSA 250,1953 model OHV
Rattles like tappet noises,but not sure,very noisy when hot and at about half reves
Adjusted the tappets many times cold to 3 thou,still noisy
Took off the head,the valve guides are worn,they flop around in the guides.Will get them rebushed
But also took off the barrel to check the little end,all is OK.
have not put the barrel on yet as i have a problem.The piston rings have no pegs to locate the rings,oil and two compression rings
Where should these be located,not in line of course.The compression bottom ring wgap was about 1/2" away from the oil ring gap,i dont think that this is a good idea
Any comments
Also with the valve springs,there is a washer at the bottom against the head,looks like a stainless steel washer that has been bored out to be used as a seat for the large spring,is this correct?Both inlet and outlet valves have the same washer,looks home made to me.
can you reuse the copper head gasket?aneal it?
any help

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From: Military-Ron Sent: 06/01/2008 14:16
Hi Birchy. It sounds to me like the valve guides are badly worn and possibly the valves. If they're flopping around like a cucuber in a bucket, it'll never be quiet. Perhaps your springs are weak and someone has put washers under to try and improve things. Sounds like a complete top end overhaul is required, Valves, guides and springs. Unlike a two stoke the piston rings are not usualy pegged. Just spin them so that the gaps are about evenly spaced around the piston. Ron

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From: fredbare7 Sent: 07/01/2008 12:11
If your rockers are worn hollow then you cannot set them accurately with a
 feeler gauge (always too wide) .
If so, then there are several answers, but a
 compromise is to work out the amout of unscrewing you need for the
right clearance. To start with, just screw right down and back off until
 free.Start the bike and see if the rattle is better, then you know you are in the
right area.

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From: sergentwoodie1 Sent: 07/01/2008 13:38
Hi there I reiterate what has already been advised by Ron & Fred, No washers should be under the springs , probably due to a previous owner, who I have said before had'nt the cash probably to spend on his/her work bike or the new springs were not available at the time. Whilst replacing/ checking the top end check the rocker is not worn.Just a bit of extra advice the C11 was prone to top end wear due to No direct oil supply It is not beyond an amatuers capabilities to make up one  I have done it to a friends C11g in fact BSA did make a kit to convert C11 valve chamber oil feed. Why not as you are stripped right down well the C11 not the owner fit new rings if the bore is not worn. Best O Luck Woodie

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From: C10Stiles Sent: 07/01/2008 19:54
Had the same thing happen to my 53 C11.
Check the cam type as you may have a later type of ramp cam that needs different tappet settings of 11 thou for the inlet and 13 for the exhaust. Also check out the cam and followers as mine were worn badly as well and with all that extra compression they can cause rapid wear on the followers and cams.
I put my ring 1/3 of the way round, eg 4, 12 and 8 o'clock
I also got a hard exhaust valve seat put in as the original was badly pitted, but the shop put the insert on the wrong side so i now have hard valve seats on both side , i only did that because it was £5.00 more than a re-seating the valve. It's not worth it if you only do a few miles.
Check out BSA service sheet 603 regarding the C11g oil feed to the top end, you can get all the bits from Draganfly. It is definatly worth the cost of around £25.00 GBP. especialy if you do short runs.
The washer is supposed to be there, it fits in between the head and the valve guide and acts as a base for the valve springs (one on each side). The part number is 15-1215. look at the 49 to 53 parts manual item 158.