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dtw dtw is offline
GAFB
 
Join Date: Dec 1999
Location: Raleigh, NC, USA
Posts: 7,547
Leakdown test on rebuilt, shelfed engine

I have a '76 2.7S CIS engine I'm working on. The story goes that this engine was completely rebuilt and then shelved (for well over 5 years). This story holds a little water, as the engine is clean and there's sealant coming out of the case halves and cam tower/head joints. The heads appear to be rebuilt, but the valves have some light corrosion on them where they're not covered in assembly lube.

Tonight I have done some exploratory surgery on the engine, one of which was a leakdown test. I'd like to hear from y'all if you think these test results are worth a flip. At first pass, the results were horrible: 40% to 100% leakdown on all holes. Went back through each cylinder and tapped on the valves with a mallet, and got down to anywhere from 0% to 30% leakdown on all holes. Majority of cylinder leakage after the 2nd pass was through the crankcase and exhaust valves. The exhaust valves had worse corrosion than the intakes.

Trying to make a decision as to whether to put induction and exhaust on this engine and try it out, or whether to take it apart and go over everything more carefully.
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Dave
'72 911T
'86 928S
'05 C4S
Old 02-18-2007, 05:34 PM
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Join Date: May 2003
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I would expect the valves to not leak on a fresh rebuild. I would expect lots of ring leak until they seat (if they were replaced).

If you have reason to suspect a problem rebuild then I'd take it apart. If you are just concerned about the leak down then I'd run the engine as is for awhile and check again.

-Andy
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72 Carrera RS replica, Spec 911 racer
Old 02-18-2007, 08:33 PM
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dtw dtw is offline
GAFB
 
Join Date: Dec 1999
Location: Raleigh, NC, USA
Posts: 7,547
Andy,
Thanks for responding on this and my other thread. I wouldn't expect the valves to leak either. Tapping them seems to free up some of the crud on the valve seats. The rings are not broken in yet, so it seems reasonable that some are losing air.

Next weekend looks like I'm retiming the cams, installing the turbo restrictors, changing to turbo exhaust valve covers, plugging the air injection ports, installing rocker seals, and checking my valve lash. That'll take a few hours but I might start getting induction on Saturday too...(why the hell did I buy another basket case 911...)
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Dave
'72 911T
'86 928S
'05 C4S
Old 02-18-2007, 09:41 PM
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Old 02-18-2007, 09:41 PM
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