7A cams in 3B head - no compression

[Ben Swann]

Bernie,

I read an old post you made:
http://www.audifans.com/pipermail/200q20v/2001-January/001791.html

It kind of looks like there is simply too much overlap using the 7A intake and exhaust
and I think with new head and all the engine is turning, but not fast enough to avoid
blowing intake right out the exhaust - 3 degrees of overlap is OK for NA, but definitely
not good for a street turbo motor.

I might be OK going with the 7A exhaust when used with the 3B intake.  Then there would
be 0 overlap according to the specs. And that should be perfect!

I don't think the cam followers are the problem.  They are lighter and AFAIK have no
more lift than the original lifters.

I will try the 3Bi/7Ae combination and if that does not work, revert completely with
stock.

I did the swap with reservation, since I've heard a lot of hoopla re. the 7A cams, but
not seen any real (read dyno testing and emissions) results.  Still I'd like to try the
combination.

Ben 

-----Original Message-----
From: Bernie Benz [mailto:b.benz at charter.net] 
Sent: Monday, January 31, 2011 11:11 AM
To: Ben Swann
Cc: 200q20V mailing list
Subject: Re: 7A cams in 3B head - no compression

Hi Ben,

AEB lifters? Is there clearance between the cam bottom and the lifter when not pumped
up, i.e. are the lifters mechanically holding the valves open?

034 uses both 7A cams and cam timing in their 3B turbo “upgrade” with claimed no
problem. But the 7A cam system has much more duration and overlap and therefore should
be subject to turbo “blow through“. Not your problem, but talk with them.

Bernie


On Jan 31, 2011, at 7:39 AM, Ben Swann wrote:

> I have virtually no compression on 3B engine that just had the 
> cylinder head redone by machine shop.
>
> The head was just rebuilt - valves ground/lapped and new seals.   
> Using AEB lifters -
> supposedly lighter.  Valve springs are stock.
>
> At suggestion of others, I installed a set of 7A cams in my 3B engine.
>
> I'm fairly confident the cams are installed correctly - 3 sets of eyes 
> on the install and alignment per Bentley - relative cam orientation 
> did not change when swapped from 7A head to the 3B head - chain and 
> cams swapped over as a unit.
>
> Engine at TDC when head pulled and while head re-installed.  Chain 
> sprockets align so the ---O-O--  are bisected by the valve gasket 
> surface.  Having done this job before many times, I'm fairly certain 
> this is correct and corresponds with the manual.
>
> However when the engine was cranked to pump up the lifters, it turned 
> over as if there were no plugs installed - no compression.  I verified 
> that there is virtually no compression - perhaps 5-10 PSI.
>
> Is it possible that the 7A cams are keeping the valves open even 
> though they are installed correctly?
>
> Just seeing if perhaps the 7A cams may not be a suitable choice for 
> the 3B, or if there is some detail that needs to be changed to use 
> them.
>
> Somewhere I recall seeing that the 7A exhaust cam is what should be 
> used, and the intake may be too much duration.  Anyone know?  BTDT?
>
> Ben
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