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48' BSA B31 tappet clearance problem
#794246 12/29/19 11:15 pm
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Hi there,
Slowly getting a 48' B31 put together and have run into a issue with tappet clearance. Original head had a crack so I found a good core and had it rebuilt and now I can't get proper tappet clearance. Its close but still too tight even with threads fully backed off. Any suggestions short of sending the head back for work? Can pushrods be shortened? Cylinder base shim? Head gasket? Argh!

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Re: 48' BSA B31 tappet clearance problem
dean toensing #794264 12/30/19 1:33 am
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I guess the valves have to come back out for grinding a few thousandths off the end of the stem. I might have used a file on the tappets once to get a couple thou, but I wouldn't tell anyone if I did.

Re: 48' BSA B31 tappet clearance problem
dean toensing #794269 12/30/19 3:00 am
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Yes, best to take it apart And grind the stem a bit.

Re: 48' BSA B31 tappet clearance problem
dean toensing #794286 12/30/19 8:04 am
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What adjusters are you using? The standard elephants foot type or mushroom adjusters? The mushroom head adjusters whilst good are not able to be backed off as far as the original elephants foot type. This can cause problems, especially if your valve seats are too deeply ground.


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Re: 48' BSA B31 tappet clearance problem
Allan G #794327 12/30/19 2:46 pm
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I'm not sure which type they are, probably not safe to assume anything since I have no history. I'll snap a picture. I had the head work done in Pennsylvania and I'm in Texas. Very reluctant to send it back for this as a fin broke in the last trip (geez what a pain!). There is a respected local engine builder who I could ask to take it apart and grind the stem a bit, I think .060 would fix my problem.

Re: 48' BSA B31 tappet clearance problem
dean toensing #794329 12/30/19 3:13 pm
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Shop may have cut the seats too deep. (makes stems to long on one end!!) i would check valve spring installed height. To tall not enough tension on spring could spit a keeper and it gets ugly. might have to shim springs to correct height. Also wonder if grinding stems will remove hardening
Keep us posted

Re: 48' BSA B31 tappet clearance problem
dean toensing #794344 12/30/19 5:03 pm
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https://1drv.ms/u/s!AsKcYdC1qRK7jm1Q9uVAi9TzrHes?e=B2D1gK


Left adjuster is BSA original, middle one is mushroom type and last one is elephant foot. Mushroom and especially the elephant foot type needs much more space than the original BSA one and was as far as I know never delivered by BSA.

Last edited by Arnstein; 12/31/19 9:58 am.

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Re: 48' BSA B31 tappet clearance problem
dean toensing #794354 12/30/19 5:27 pm
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Just got back from engine builder. He said to check to see if a copper ring should be used between head and barrel before we do anything! I was under the impression there was nothing used as a seal or gasket. Please oh learned ones what is the correct setup?

Re: 48' BSA B31 tappet clearance problem
dean toensing #794377 12/30/19 10:22 pm
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There isn't a head gasket on the early B's but my B33 has a base (decompression) gasket which is around 1mm thick.


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Re: 48' BSA B31 tappet clearance problem
Manx #794387 12/30/19 11:35 pm
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Thank you, I'm going to take the head in tomorrow. The machinist said about $100 to trim the valve stems.

Re: 48' BSA B31 tappet clearance problem
dean toensing #794391 12/31/19 12:44 am
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Hi
Quote
The machinist said about $100 to trim the valve stems.


Robbing B&^^***rd
5 minutes work

John

Re: 48' BSA B31 tappet clearance problem
dean toensing #794395 12/31/19 1:23 am
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Dean: Does your 48 engine have the same tappet adjusters as the later B31/33 engines?

Like these? Something different?

Gordo

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Re: 48' BSA B31 tappet clearance problem
Gordo in Comox #794412 12/31/19 2:26 am
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I would say that is the type I have.

Re: 48' BSA B31 tappet clearance problem
dean toensing #794415 12/31/19 2:32 am
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John its not 5 minutes to disassemble the head grind the stems and reassemble the head.

Re: 48' BSA B31 tappet clearance problem
dean toensing #794417 12/31/19 3:02 am
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Dean: Given how much that type can be adjusted as compared to the eccentric Gold Star setup there has to be something really amiss in the valve train.

However when I look at the amount of threads on the cam follower and how short the engagement peg is on the pushrod I would think that you could shave a little off the locking nut (on far right in second photo) so that the engaging nut could be threaded little further down onto the cam follower stem. A few thou would be easy to attain.

The only snag would be that the rocker geometry could be seriously incorrect. If you are using the standard 2420 cams then the geometry change might not matter given the limited lift they provide.

Gordo

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Re: 48' BSA B31 tappet clearance problem
Gordo in Comox #794461 12/31/19 3:03 pm
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Thank you Gordo, I am at a loss on this also. With the original head there was adequate adjustment but that head was cracked. So I found a nice rebuildable head from someone here. He was willing to send it directly to a respected machinist for rebuild. He cut new guides and valves. I guess I'm thinking take the head apart and start measuring. Argh

Re: 48' BSA B31 tappet clearance problem
dean toensing #794475 12/31/19 6:00 pm
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At least with the B31 you can take off the valve covers to see what is happening between the rocker and the valve stem. I presume you are measuring the clearance down at the bottom of the pushrod but I am curious if at anytime during the rotating of the engine if there is any point where there is some clearance. Do the valves ever fully close as the engine is rotated?

Gordo


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Re: 48' BSA B31 tappet clearance problem
dean toensing #794477 12/31/19 6:32 pm
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Yes looking for gap at the adjuster, would say closed but no clearance. I think this head is from a later year. Perhaps some differences as a result? Machinist said he will look at valve spring heights and forces. We shall see.

Re: 48' BSA B31 tappet clearance problem
dean toensing #794495 12/31/19 9:21 pm
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Hi Dean,
What I meant was that it only takes 5 minutes to shorten the valves themselves
a couple of minutes to remove the valves and springs and maybe 10 minutes to replace them
At least thats how long it would take me.
Not including any other work that was found to be required
A useful dodge on B31's with a sunken inlet valve seat is to substitute a Triumph T120 inlet valve
The larger Tri valve head will sit near enough where the BSA one should be without having to resort to fitting a new seat
The Tri valve will need a little shortening if fitting the lash cap, but they have hardened ends so will work without
I have rebuilt quite a few B31/B33's so feel qualified to comment
B31's &33's can be fun boosting their performance substituting some "goldie" parts

John

Re: 48' BSA B31 tappet clearance problem
dean toensing #794505 12/31/19 11:36 pm
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Thanks John,
You are way more knowledgeable on this than me.
I'm kinda kicking myself on this which is not easy to do.
Dean

Re: 48' BSA B31 tappet clearance problem
dean toensing #794562 01/01/20 4:39 pm
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Sounds to be the opposite of the problem I had with my B31. On mine the pushrods were shorter than they should be as the tubular part had flared out slightly where it joined the hardened steel end part. If I recall correctly this resulted in the rockers hitting the edge of the valve spring caps.

Re: 48' BSA B31 tappet clearance problem
dean toensing #794587 01/01/20 9:33 pm
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Hi Fido and All
Quote
If I recall correctly this resulted in the rockers hitting the edge of the valve spring caps.


This would seem more likely if the valves were very recessed in the head ???

confused
John

Re: 48' BSA B31 tappet clearance problem
dean toensing #794616 01/02/20 10:34 am
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It is a long time ago so I can't remember exactly what was happening but new pushrods cured the fault.

Re: 48' BSA B31 tappet clearance problem
dean toensing #794648 01/02/20 9:45 pm
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Hi Fido
Quote
I can't remember exactly what was happening


LOL
Time is the enemy of memory
I am finding it harder and harder to remember yesterday help

beerchug
John

Re: 48' BSA B31 tappet clearance problem
dean toensing #797140 01/31/20 9:14 pm
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Ok, finally we have the valve rocker clearance problem fixed. The valve stems were a bit long, the machinist cut .060 off. He checked the valve spring pressures etc everything looked good. So for final assy I read somewhere that its a good idea to lap the head to the cylinder, should I do this? Any other good assy practices? Thread sealers? Copper gasket paste? Any suggestions are welcome.
Dean

Re: 48' BSA B31 tappet clearance problem
dean toensing #797150 01/31/20 11:11 pm
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Hi Dean,
There are inner and outer lands on the cylinder and head
Use fine paste on the inner land and coarse on the outer
Lap until both areas show an even contact all over
The coarse paste on the outer areas should provide a very small clearance when the inner area is seated
This method should ensure that there's a gas tight joint at the inner lands when the head bolts are tightened
I just put a very light smear of grease on the joint areas
Run a few drops of oil down into the head bolt fittings in the crankcase, inside those fittings are the area's subject to friction when tightening
the head bolts

John

Re: 48' BSA B31 tappet clearance problem
dean toensing #797174 02/01/20 2:56 am
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Thank you John!

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