Valve stem height question

[Hercplt]

I'm pretty confident that its the rings at this point... I might put pressure on it again and see what I hear.  With the valves re-lapped and an increase of only 10 psi indicates that the valves did their job and we removed a source of leak.

Head gasket that in installed looked great when I removed the head for the second time... the original was likely not torqued properly in the first place.

To answer another question above... the head was already ported, and large valves added... CC opened up and skimmed to get the CR up closer to 10:1.

I think opening it up to renew the rings and bearings... and a light honing should do the trick.

Thinking of replacing the VP7 with the SW5 cam while I have the chance.  Should make a much nicer street 998, rather than the VP7 which (in the 998) is a bit lumpy and comes on too late.

[MiniDave]

Without knowing the specs on the VP7 vs the SW5 it's hard to say, but I've been using the Evo1 cam from Spares which is supposed to be about the same as the SW5 and it works well, plenty of torque down low.

[94touring]

10:1 should be seeing 180psi or so fyi. 

[tsumini]

Two things.
1. Re-read thread and saw that you reported the engine didn't smoke at all. Ring blowby and poorly installed rings leaking should smoke more the snoop dog.
2. Photo shows the relative height of exhaust/intake valves of a head I redid several years ago. The valves were eyeball level. You showed your head as being quite eyeball mismatched. I think was dismissed as being not usual but not a deal breaker. Today i stumbled  on forum discussing a very similar problem except diesel and was 50 psi short on an expected 300 psi and exhibited the same running  problems.
Someone suggested that valve seats were ground too deep and resulted in sinking the valves deeper into the head and expanding the combustion chamber volume and thus reducing compression ratio and compression itself. Wondering if your valves are too deep.
If it was mine I would measure the CC volume and establish actual CR and at least verify head is good. It may be worth it to avoid ring teardown. IMO lapping didn't do much and didn't prove head was good.
I'm kinda throwing this out cuz my gut tells me there is something wrong in your head. :-[ Excuse PUN

[Hercplt]

Tsumini;

I understand what you are saying regarding the valves coming in at different heights.  Problem is that all the intake valves and all the exhaust valves match respectively.  It was like this when first built and the thing was a rocket.

I will very likely have the head looked at in detail by someone more knowledgeable than me... and maybe re seat it..

When I put the whole story together (i.e. sitting for so long... hearing air pass into the crankcase, compression test results)... the logical conclusion is rings.  Having said that, either way you look at it I am very likely going to have to open it up anyway and check for damage.  I suppose that if there is none... then we can button up and go from there.

It is a good opportunity to set the motor up the way I have always wanted anyway... more torqy cooper style cam (SW5) rather than the faster road cam... that sort of thing.

Interesting stuff...

I've always wanted to know what this engine could do with the SW5...

[tsumini]

Hercplt, No worries. Just trying to suggest a few things to look at to avoid going after the rings. I recall on mine  that when compressed air was introduced I heard hissing in the sump from rings bypassing but could never determine if it was normal or excessive.
Good luck with your rebuild and hope to hear good results.
PS I re-read the thread and you did say it had run nlike a banshee at one point but i missed that.
Good luck again.

[jeff10049]

Hercplt, No worries. Just trying to suggest a few things to look at to avoid going after the rings. I recall on mine  that when compressed air was introduced I heard hissing in the sump from rings bypassing but could never determine if it was normal or excessive.
Good luck with your rebuild and hope to hear good results.
PS I re-read the thread and you did say it had run nlike a banshee at one point but i missed that.
Good luck again.

Yes without an actual leak down tester its hard to guess whats normal because they always have some blow by. Then again I've had engines with 70% past the rings run very well.  I also have a gut feeling the head could use a complete valve job and go through the rings and bores as well just give the whole thing a check out.