Headgasket or not??!

larby · 23-05-2008, 08:09 PM

Hi everyone!

I've recently bought a 1999 2.5 200 carb powerhead, in boxes.
Seems to have gone together ok so far but i've got a major problem with the headgaskets!

I can't find the serial number anywhere so i went with the gasket outboard and hydroplane said was correct, but it'd seem it's wrong...

I've only got about 75 - 90 psi on each cylinder, and having looked closer at the manual it seems to suggest the 200 uses a series of 'seals'... a ring around each clyinder and then a seperate outer one, not a 1 piece headgasket like i've got in there

I'm totally confused and don't know what to get next, wouldn't have expected just the wrong gasket to make that much difference to compression either... What do i do?! Someone out there must have one of these and know what to do??

Cheers in advance...

James

larby · 23-05-2008, 09:09 PM

Also if anyone would know what part numbers i would need that'd be great... I can't see a reason why i couldn't run any hi-performance 2.5 headgasket?

Cheers

BluFin · 23-05-2008, 10:14 PM

Have a look at the BAM marine online parts catalog. Just need your eng serial number, Its stamped on the block so you should be able to pin it down

BAM Marine online parts

at least you can sort the right P/N

larby · 24-05-2008, 12:03 AM

cool, thanks for the link... I've checked the block over several times and just can't find a serial number anywhere... The circular disk on the top is blank and there's only a few other odd numbers on it, nothing resembling a serial number. That's where my biggest problem lies!

BluFin · 24-05-2008, 07:23 AM

port side of engine block on outside flange at crankcase joint. They also put them on the leg small data plate (Saddle or tilt pin)

SCOTT671 · 24-05-2008, 09:16 AM

if you check out this web site it has a model/year identifer on it

http://www.maxrules.com/modelindex.html

200 Carb V-6 2.5 Litre / 153.0 cu.in. 1991/1999 sn 0C291520------0G960499

hope this helps

larby · 24-05-2008, 10:16 AM

thanks for the link scott, it only goes up to 96 for the 200's though

Also the service manual i got with the engine is for 0G960500 and above... Hence my complete and absolute confusion!!!

I just can't see how just the wrong headgasket could drop the compression right down to 75psi!!

SCOTT671 · 24-05-2008, 10:22 AM

Quote:

Originally Posted by larby

thanks for the link scott, it only goes up to 96 for the 200's though

Also the service manual i got with the engine is for 0G960500 and above... Hence my complete and absolute confusion!!!

I just can't see how just the wrong headgasket could drop the compression right down to 75psi!!

Larby if you have chance you could phone them and ask there adviceas they are very helpful

Bill Kelly, the MasterTech

PHONE: 850-623-1197

larby · 24-05-2008, 10:23 AM

Quote:

Originally Posted by BluFin

port side of engine block on outside flange at crankcase joint. They also put them on the leg small data plate (Saddle or tilt pin)

I've just been out and checked this again, also checked the other side for good measure, there's nothing. A few random numbers, and what looks to be a date stamp, 8 19 98, but nothing that looks like a serial number!
How on earth can it just have no serial number??!

larby · 24-05-2008, 10:25 AM

Quote:

Originally Posted by SCOTT671

Larby if you have chance you could phone them and ask there adviceas they are very helpful

Bill Kelly, the MasterTech

PHONE: 850-623-1197

Thanks, i might give that a try. The dealer over here isn't that great, they're helpful, but only to a certain degree. If it's not making them money and completely standard, they don't wanna know!

Cheers

larby · 24-05-2008, 10:39 AM

ok, so going by various bits on the engine, flushing outlet, known cowl shape etc, i've managed to work out that it's part of the 0G960500 > group...
Going by that parts link (thanx blufin!) it uses seperate round 'seals' and then an outer seal, instead of a headgasket.. Has anyone used these before?? It looks a bit odd to me, i don't recall seeing anywhere for what looks like an o-ring to locate??
I'm hoping someone can help before i lose all hope and give up completely!

Thanks for all the help so far!

Frenchbruno · 24-05-2008, 01:28 PM

Hi everybody,

you are using the latest merc 200 carb serie (0G960500 THRU 1B226999), and if you are sure of the head shape, you need to use:
2 x MM-8584521 17.23$ each
6 x MM-8597721 7.52 $ each

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And remember, for a good comp pressure test you must have the engine kill switch to "kill engine position" and the throttle have to be wide open , not in iddle position. Also your starter battery at the maximum capacity for the test. You cannot make a good comp test with the carb throttle shutter in iddle position. Use the same procedure for all cylinders...
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larby · 25-05-2008, 11:58 AM

thanks Bruno, that's a good description of pressure testing there! I always zip tie the throttle wide open to do it, then just use a snap-on peak hold gauge.

I've managed to solve the problems i think... it looks like i just han't cleane up the surfaces up enough, i spent most of yesterday clening them up with wet & dry on a file wih lots of WD40, and compression is now up to 95psi even across all cylinders. I think it may be low because it's only dry built, the gauge may also be out for all i know... the most important thing to me is that they're even... if needs be then i'll get some tighter heads.

Thanks to Roofer for the motor, looked like a right mission to start off with, but now it's all together i realsie what a bargain i got!! He even put up with my worried emails

Thanks again for all the help on here guys, couldn't do it without you!

Frenchbruno · 25-05-2008, 12:46 PM

ok,
you should have something arround a 125 psi comp pressure on your engine.
But have a look on your reeds, if you are using rubber seat with stainless reeds, they can be curved a little bit, and leak a little bit. That's mean you loose final compression pressure. If it's the case the best way is to buy a set of boysen reeds in dual stage .
It's easy to see, remove the air filter, wide open the trottle, use a good torche and you can see if every reeds are in contact with the reeds block.

larby · 25-05-2008, 07:08 PM

they are all lifted off ever so slightly, only by a thou or 2 though... I'll look at changing them soon. Took it out today and she ran really well, need to try a different prop the once i've got it running ok I'll look into changing it further, should have the money to do it then too!