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914World.com _ 914World Garage _ Valve guide position 1.7 liter heads
Posted by: pgollender May 19 2017, 08:30 AM
After hot tanking I noticed different lengths on my exhaust valve guides. Between the four exhaust guides ( two heads) the length of the top of the guide out of the head varied by 2 mm. Is this a problem or just sloppy work from P.O. ?
Does it matter ?
Posted by: malcolm2 May 19 2017, 09:32 AM
It is not easy to find pictures of cylinder heads without valves. But here is one.
looks different to me.
Posted by: Mark Henry May 19 2017, 07:04 PM
They're driven in, check the seat side I bet they look like they're extra long.
Even the left hand exhaust guide looks like it's sunk in too far, could be just the angle.
Cause is likely they were loose and should have had OS guides.
Bad valve float can drive them in as well.
Surprised the boss isn't cracked.
They must be cored and driven out from the camber side, then see if they are salvageable.
Yes poor machine work and yes it does matter.
Posted by: HAM Inc May 19 2017, 07:52 PM
After hot tanking I noticed different lengths on my exhaust valve guides. Between the four exhaust guides ( two heads) the length of the top of the guide out of the head varied by 2 mm. Is this a problem or just sloppy work from P.O. ?
Does it matter ?
The factoryguides didn't have shoulders. They'd slip down. Saw that a million times. It never hurt anything when they didn't slip down more than in the picture. Sometimes after slipping they would loosen further and start moving up and down in the guide bore. That would cause problems.
I can't tell if the exhaust guides are O.E., but they didn't have a shoulder either. They weren't as prone to slip as the intakes. The intake guide bores on the 1.7 are really short. The exhaust are pretty long, so the guides weren't as prone to slip.
Posted by: pgollender May 20 2017, 09:11 AM
"They must be cored and driven out from the camber side, then see if they are salvageable."
Can you explain this comment a little more.
I understand the part about cored and driven out, but not the "salvagable" part of your comment.
I have never rebuilt 914 heads personally before, always had a machine shop do it for me.
The boss surfaces and intake surfaces look intact (no magnaflux test) . I can't see any visible cracks between intake and exhaust ports or to spark plug hole.
The current guides appear to be quite tight,and I can elicit no guide wobble within the bore itself.
Not sure how to test the angle of the guide.
Is there another step that requires evaluation of the guide bore hole that you are referring to ?
Also what is the correct finished height of the guides above the boss surface once installed ?
Posted by: Mark Henry May 20 2017, 10:39 AM
"They must be cored and driven out from the camber side, then see if they are salvageable."
Can you explain this comment a little more.
I understand the part about cored and driven out, but not the "salvagable" part of your comment.
I have never rebuilt 914 heads personally before, always had a machine shop do it for me.
The boss surfaces and intake surfaces look intact (no magnaflux test) . I can't see any visible cracks between intake and exhaust ports or to spark plug hole.
The current guides appear to be quite tight,and I can elicit no guide wobble within the bore itself.
Not sure how to test the angle of the guide.
Is there another step that requires evaluation of the guide bore hole that you are referring to ?
Also what is the correct finished height of the guides above the boss surface once installed ?
Just take it to your machine shop, preferably one with aircooled engine knowledge.
As Len (HAM) said guide slippage and I said guides are sunk deeper than normal, so the guide must be removed, reamed and OS (oversize) guides installed.
Guides may appear "tight" to you, but as soon as the head is warm they are loose.
Sitting down flush like that is not normal.
Posted by: porschetub May 20 2017, 02:55 PM
Sorry double post.
Posted by: porschetub May 20 2017, 03:01 PM
then this 
I have a 1.8 bus head that did this with minimal piston head damage ,how lucky is that ??
Posted by: pgollender May 21 2017, 08:38 AM
[/quote]
Guides may appear "tight" to you, but as soon as the head is warm they are loose.
Sitting down flush like that is not normal.
[/quote]
Thanks Mark,
I didn't know that about the guides.
Understanding the problem helps me to evaluate the work expected from the machine shop or in the future when buying the next set of heads what to look out for. Or in case of failure, the etiology of the problem.
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