454 compression test question
04-10-2016, 05:16 PM
#31
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Almost forgot....I think they are 454 340hp mercs....I'll have search difference between the 330hp I thought it was and the 340hp they are.
Last edited by deputydog; 04-10-2016 at 05:19 PM.
04-10-2016, 05:19 PM
#32
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Per mercruiser recommended ranges and test procedures regardless what many might not know or think. Just putting it out for info.
http://www.boatfix.com/merc/bullet/97/97_25.pdf
http://www.boatfix.com/merc/bullet/97/97_25.pdf
04-10-2016, 06:56 PM
#33
04-10-2016, 07:41 PM
#34
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Mercruiser in the service manual for 1993 thru 1997 big block 454 and 502 listed the compression pressure at 150 psi for all black production side engines. Then in 1999 Merc listed the SB as I already posted as they wanted a min of 100 psi and no more than a 30 % difference between the lowest and highest psi cylinders.
With that said many marine techs go by a 15 % to 20 %. from the highest to the lowest cylinders.
With that said many marine techs go by a 15 % to 20 %. from the highest to the lowest cylinders.
Last edited by BUP; 04-10-2016 at 07:47 PM.
04-10-2016, 08:09 PM
#35
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That's surprising. Not doubting it at all just surprising especially with an expected engine running for long periods time at higher rpm. So in this case here at 24% they'd without a doubt further diagnose.
04-10-2016, 08:09 PM
#36
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I was just going off general engine knowledge. I know the manual says 150psi, but it also says 8.0:1 static in one section, and 8.5:1 in another section, for the 330.
The 330 engine was the L19 GM shorblock, with peanut port heads. The only real difference was the cam, was larger than the truck engine's cam, longer duration. That engine was 7.9:1 static. I don't see how they would get 150psi cranking with that engine combo. I had a couple of those engines in trucks over the years, and 130psi on the starter was the norm, and that was with a really short towing camshaft they had, shorter than the 330 merc camshaft.
The higher compression "mag " engines, with the dome pistons, would crank closer to 150ish.
The 330 engine was the L19 GM shorblock, with peanut port heads. The only real difference was the cam, was larger than the truck engine's cam, longer duration. That engine was 7.9:1 static. I don't see how they would get 150psi cranking with that engine combo. I had a couple of those engines in trucks over the years, and 130psi on the starter was the norm, and that was with a really short towing camshaft they had, shorter than the 330 merc camshaft.
The higher compression "mag " engines, with the dome pistons, would crank closer to 150ish.
04-11-2016, 01:23 AM
#38
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everything depends on what it was repowered with. in 97, it could have been a round port 8 to 1 motor or L29-ish oval port 9 to 1 motor. and were they bought complete new as a package from merc or crusader et al, or rebuilt by bob's engines with whatever bob may have had laying around...
04-11-2016, 02:44 AM
#39
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I agree on everyone about the numbers and some versions being closer to 150 and others closer 130...heck my 67 pontiac has 13to1 comp motor and cranks at 240psi with big roller cam. I'm just confused and trying figure out why the 5 and 6 cylinders and both engines are 95 when all rest are acceptable.
Dereknkathy...you mentioned the fiberglass tanks. Yes there still in there and that was the one thing I planned replace and how I got the sale price to 30k for a very clean and updated bertram. The prior owner had it 8 years and has never run ethenol in the tanks. The majority of the gas docks in my area are non ethenol.
I spoke second owner who owned boat from 1977 until 2000. The repower was takeouts from a new Chris craft charter boat his friend had. The gas engines were used slightly for one season and taken out to put diesels in. The second owner bought the entire gas setup and installed it in the bertram.
If the heads need come off I can deal with that but even at 30k for nice solid bertram if the engines need come out may have reconsider or pass if the seller doesn't want drop price due to low compression.
Dereknkathy...you mentioned the fiberglass tanks. Yes there still in there and that was the one thing I planned replace and how I got the sale price to 30k for a very clean and updated bertram. The prior owner had it 8 years and has never run ethenol in the tanks. The majority of the gas docks in my area are non ethenol.
I spoke second owner who owned boat from 1977 until 2000. The repower was takeouts from a new Chris craft charter boat his friend had. The gas engines were used slightly for one season and taken out to put diesels in. The second owner bought the entire gas setup and installed it in the bertram.
If the heads need come off I can deal with that but even at 30k for nice solid bertram if the engines need come out may have reconsider or pass if the seller doesn't want drop price due to low compression.
04-11-2016, 05:19 AM
#40
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the leakdown test already showed you it was valves. and there are SOOOOO many sets of peanut heads laying around. I am not sure if I have 1 set or 2 right now, plus a couple sets of l29 heads. and that is just 1 guy on here. and no I am not trying to sell them to you. OK, so they are merc engines, exhausts. start shopping for 4 of these. they are no longer available new. http://www.ebay.com/itm/MERCRUISER-5...dW1jFm&vxp=mtr I assume closed cooling system? are the exhaust manifolds antifreeze or raw water cooled? you are still not sure which engines you have. gen5 round port or gen 6 oval port. how many bolts on the timing covers? 6 or 10?
