Author Topic: B31 loose valve guide  (Read 282 times)

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chrisgoodwin

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B31 loose valve guide
« on: 31 August, 2017, 22:34:26 »
Hi all,
Head and barrel now stripped, the plan was a thorough clean and paint, but I have come across a problem, the exhaust valve guide was loose with about 1/8" play up & down.
I made a drift and knocked the guide out, after the initial play the guide was tight in the head.
When the valve was put in the guide it is "sticky" at the point where the valve would have been in its seat.
New valve and guide obviously required, but I am unsure what to do to make sure the problem does not reoccur.
New guide with Loctite and hope for the best? Can you buy oversize guides (I remember doing that to a Triumph years ago) or will the guide hole need reaming and a guide made to suit?
I'm a bit stuck on this one, and as ever any advice is really welcome.
Cheers
Chris

Greybeard

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Re: B31 loose valve guide
« Reply #1 on: 01 September, 2017, 08:39:08 »
Hello, Chris.
I had a similar problem on a late B31 I had years ago. A local engineering company found that a new guide was also a bit loose in the head so they knurled the outside of it which increases the diameter slightly and used an engineering grade loctite (I dont know which one) It was before the time when I had the cash to buy my own tooling for that sort of job so I wasn't able to do it myself.
So all is not lost and can easily be solved. The bike had no problems after that - wish I still had it  ::)

Steve
Steve from East Yorkshire - Not the Greybeard of the A7/A10 forum who was not actually registered on this one when I signed up ;-)

paulm

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Re: B31 loose valve guide
« Reply #2 on: 01 September, 2017, 08:51:52 »
knurling is not a goot idea, you need the hole reamed round and a oversize guide made any competent engine reconditioner can do this , but be careful use BSA running clearences as these are prone to nipping up if machined to car clearences if your purse can stretch cylinder head shop in London

JulianS

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Re: B31 loose valve guide
« Reply #3 on: 01 September, 2017, 09:30:56 »
If you try loctite, and I would advise against, then you need to choose and try a specialist grade;

http://na.henkel-adhesives.com/product-search-1554.htm?nodeid=8797931798529


But why risk it when there is a sound and proven engineering solution with oversize guide.

Trev

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Re: B31 loose valve guide
« Reply #4 on: 01 September, 2017, 09:45:15 »
Quote
cylinder head shop in London
Yes, I agree, he did my A10 ally head wich had the exact same problem that you describe. Made a very good job of it. http://cylinderheadshop.com/ and of course he knows the correct tolerences wich is important.
« Last Edit: 01 September, 2017, 09:51:55 by Trev »

chrisgoodwin

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Re: B31 loose valve guide
« Reply #5 on: 01 September, 2017, 23:01:37 »
Thanks for the replies, I'll get the hole reamed, checked and a new guide made.
If a job's worth doing it's worth doing right.
Cheers
Chris

chrisgoodwin

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Re: B31 loose valve guide
« Reply #6 on: 03 September, 2017, 22:09:41 »
Sorry to drag on but I am trying to get my head round this, as I understand things, the notional diameter of the valve guide is 5/16th? Taking tolerances' into account - in a perfect situation should the hole in the cylinder head be 5/16th and the guide itself be slightly bigger to accommodate the interference fit?

If the valve hole has worn what should the diameter of the hole be to accept +2 or + 4 though dependant on wear?

Thanks in advance,
Chris

paulm

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Re: B31 loose valve guide
« Reply #7 on: 03 September, 2017, 22:46:03 »
if the guide hole is worn there are no rules, I would say ream it to take out the least amount possible then have a guide made, you can buy a oversize guide but as you really need them reaming after fitting i would have it made it suit and reamed in situ letting the same person recut the seat to ensure its sqaure, this is not as expensive as it sounds