V6 lower two cylinders, lower compression?

[johnyrude200]

I have a 1987 V6 loop charged OMC. I believe I read T2stroke said the lower two cylinders will have slightly lower compression numbers; is this true and if so, why?

Thanks

• This topic was modified 5 years, 3 months ago by johnyrude200.

[dan-in-tn]

{contentNot on that early of model. Started with 1992 60* 150/175 if memory serves me correct? Called staggered combustion chambers. Bottom two cylinders will show 5 to 7 lbs less compression. You can tell if you have one of these cylinder heads by how deep the spark plug recess is. The two bottom spark plug holes will be shallower for the threaded area. That is because the combustion chamber is deeper. It’s the easiest way to tell without pulling head. Part number is dykem on head, but sometimes has been washed/wore off.

Dan in TN

}

[fleetwin]

Like Dan says…..I think this concept carried over to other V6 models also. Your 1987 loop V6 might have one of these powerheads if the powerhead has been replaced….Have a look at the ID plug on the powerhead. This idea was supposed to help protect the lower cylinders from detonation/preignition damage because they got hotter….

[johnyrude200]

OK, thanks, good to know. This powerhead was part of a lot clear out sitting on a pallet; so it is not mounted on an exhaust housing and exposed to dry air for the better half of a decade. The numbers were all 105-120, with bottom two cylinders a little bit less (say 95-105), so I’,m thinking some stuck/dry rings. There was a bit of mouse nesting near the exhaust orifice too so the fabric/cardboard nesting materials probably did a good job of wicking away any oil/moisture that was in the cylinders.

I pulled both heads and don’t see any red flags in terms of scoring on the bottom two cylinders. The powerhead is bone dry.

Hope the freezingham meet was a great one yesterday!

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