7A cams in 3B head - no compression

[Bernie Benz]

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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