Author Topic: Valve guides  (Read 1715 times)

Offline bikerboy

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Valve guides
« on: 05.07. 2013 04:15 »
Out of curiosity as I have a couple of heads I am doing up how does one know what oversize valve guides to get ?

Is there a standard measurement for the hole in the cylinder head and how much bigger than the hole do the guides have to be ?

I know I will need at least two new guides and am assuming they will need to be oversize

Online muskrat

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Re: Valve guides
« Reply #1 on: 05.07. 2013 09:26 »
Alloy or iron head? Iron or bronze guides?
If you don't suspect they are loose, just worn. I've heard good reports on K Liners. I'm going to try them next time mine need doing.
http://cylinderheadshop.com/k-line-guide-liners/
"Our best result was with one customer who, after 50,000 on his BSA A10, still had 2 and a half thou or less clearances valve to guide. Less than they would have been when they left the factory. "
Cheers
Std guide size is 0.560", 0.002" shrink fit so hole is 0.558", guides come in 1,2,4,10 thou oversizes.
'51 A7 plunger, '57 A7SS now A10CR, '76 XT500, '77 AG175 '83 CB1100F, '81 CB900F project.
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Offline Briz

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Re: Valve guides
« Reply #2 on: 05.07. 2013 13:38 »
An alloy head is much more likely to need oversize guides than an iron one.
You wont know until you remove the old ones and measure the holes.
I'd always prefer a bit more interference on an ally head; 3-4 thou. Especially if you choose iron guides.

Offline bikerboy

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Re: Valve guides
« Reply #3 on: 06.07. 2013 02:53 »
Its an alloy head I should have mentioned that (doh)

The last time I used it there was oil coming out from around the exhaust so I assume the guides are pretty well knackered

Offline bikerboy

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Re: Valve guides
« Reply #4 on: 06.07. 2013 03:37 »
Briz

I thought you had to use the bronze valve guides in an alloy head ?

Online muskrat

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Re: Valve guides
« Reply #5 on: 06.07. 2013 03:52 »
It is best to use bronze guides in an alloy head, and can get away with just 2 thou shrink. If using iron guides in an alloy head it would need to be 3-4 thou as Briz says due to the different expansion rates.
Cheers
'51 A7 plunger, '57 A7SS now A10CR, '76 XT500, '77 AG175 '83 CB1100F, '81 CB900F project.
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Muskys Plunger A7

Offline BSA_54A10

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Re: Valve guides
« Reply #6 on: 06.07. 2013 11:18 »
As for K linners.
I would have no worries about fitting them to the inlets.
However I have heard of a few where the exhaust either grabbed the valve or got dragged out by the valve.
Weather they were done by some one competant with air cooled engines is another question.
Bike Beesa
Trevor

Offline bikerboy

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Re: Valve guides
« Reply #7 on: 07.07. 2013 02:55 »
Cheers Muskrat I will stick with the bronze ones me thinks

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Re: Valve guides
« Reply #8 on: 07.07. 2013 09:42 »
If when you push them out (and they are std size) you see alloy deposits on them (scoring from the removal) I'd go for 1 thou over.
If doing a virgin head *eek* I always go 1 over.
Cheers
'51 A7 plunger, '57 A7SS now A10CR, '76 XT500, '77 AG175 '83 CB1100F, '81 CB900F project.
Australia
Muskys Plunger A7

Offline shabashow

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Re: Valve guides
« Reply #9 on: 07.07. 2013 11:02 »
Yes I would agree with BSA 54A10 -
"As for K linners.
I would have no worries about fitting them to the inlets.
However I have heard of a few where the exhaust either grabbed the valve or got dragged out by the valve.
Weather they were done by some one competant with air cooled engines is another question."

Yes I would agree that it is risky on the exhaust side of the A10 - Both of mine went. I found one mushroomed, as it had been pushed down a half inch or son, I found the other in the exhaust pipe! Don't know how long I was driving around like that, my last trip was a 500 miles round trip up the the extreme north west of Scotland, then back to civilisation. She went beautifully all day.

When I took the head back to my engineer, who fitted the k liners a few years previoiusly, he was initially stumped. He's fitted thousands over the years to all sorts of engines, and up until that point he only had one that slipped. I trumped that with 2 in one engine! After a bit of thought, and looking at the state of the head, it looked like I had been running far to hot, either a timing or mixture fault. (fixed now) This would have expanded the valve stems which then nipped the liners and moving them. Standard guides now fitted to exhaust, the inlets still have the liners in them, they will probably out last me. If the engine wasn't run so hot, the exhaust liners would still be in place.

Offline bikerboy

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Re: Valve guides
« Reply #10 on: 21.07. 2013 02:08 »
Well I might put refurbishing that head on hold  ;)

After stripping it I found it has the super big 67-961 valves on the inlets and they are about £35 each  *sad2*

Online bsa-bill

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Re: Valve guides
« Reply #11 on: 21.07. 2013 12:43 »
I believe the difference between super big and normal is a very few thou
All the best - Bill
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Offline bikerboy

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Re: Valve guides
« Reply #12 on: 22.07. 2013 00:48 »
Bill

I think its about 40 thou so if push comes to shove I can probably use the 67-1551 valves