Compression lower Cylinders 4,5,6

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enkai74
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Compression lower Cylinders 4,5,6

Post by enkai74 » Fri Aug 08, 2014 12:32 am

Hi guys,

Just compression tested the 2.5 V6 12 valve.

Right Bank of cylinders:
1 185
2 182
3 187

Left Bank of cylinders:
4 165
5 160
6 162

Engine warm, 10 cranks, all plugs out.

I think it's strange that one entire bank is lower than the other bank.. Causes?

1. Left Head thickness is greater than Right Head thickess - I suppose I could measure this
2. Cylinders 4,5,6 have worn rings - Possible oil gallery problem on the Left side?

It's been about 14 years since I last built and diagnosed engines, so any thoughts or ideas would be appreciated.
Nico

85 GTV6
80 GTV2000

"never fast enough"
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75evo
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Re: Compression lower Cylinders 4,5,6

Post by 75evo » Fri Aug 08, 2014 10:30 am

How about cam timing and valve clearance? Because those compression values are measured dynamically you need to double check those 2 things I mentioned. But it's possible that a previous owner replaced a head, or shave it. Now is a good chance to take both heads and get 200 psi on both sides!
Greg Gordon
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Re: Compression lower Cylinders 4,5,6

Post by Greg Gordon » Sat Aug 09, 2014 2:27 pm

When one bank is lower than the other, it's usually because cam timing is one tooth off on the lower bank.

Greg,
www.hiperformancestore.com
www.okinjectors.com
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enkai74
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Re: Compression lower Cylinders 4,5,6

Post by enkai74 » Sun Aug 10, 2014 2:59 am

Thanks Greg, that does sound like the problem, the engine lost some power and started popping through the exhaust at idle... And so the process of elimination started. It's amazing how many issues you can find when you start looking... Over the last week it's been a bunch of 2%ers....popping still there though.

The belt is tight, there's a very slight leak at the tensioner, the issue started instantly on a hot start, I'll pull the covers and check.

Thanks again.
Nico

85 GTV6
80 GTV2000

"never fast enough"
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enkai74
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Re: Compression lower Cylinders 4,5,6

Post by enkai74 » Mon Aug 18, 2014 2:07 am

Greg Gordon wrote:When one bank is lower than the other, it's usually because cam timing is one tooth off on the lower bank.

Greg,
http://www.hiperformancestore.com
http://www.okinjectors.com
Fixed, one tooth out. Thanks.
Nico

85 GTV6
80 GTV2000

"never fast enough"
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