Merc VS GM Gaskets

[John_S]

As some of you know, I am updating my '97 Mercruiser 5.7L with vortec heads, Merc roller cam and 4brl carb & manifold. I have been wading through some of the possible gasket choices. From dis-assembling the parts, some gaskets appear to be Merc specific while others seem to by just GM.

I am OK with paying more for Merc gaskets when they are made different for the application. I don't like paying a premium for just relabeled parts. ie like the vortec heads themselves.

I believe the exhaust gaskets are Merc specific:

Exhaust: 27-33395
Riser: 27-863724
Elbow: 27-863726

Composite Timing Cover Merc: 835005 appears to be standard GM. $50 vs $21.

Intake Gasket: Merc: 27-807473A1 appears to be standard GM vortec. Same list price, but you can find the GM for about $10 less.

Head Gasket: Merc: 27-75611. I found a referance to a GM equivelent 12557236 (description below). Is this correct? 0.051 seems rather thick?

Yea, I know, nowhere near 0.040 quench, but then merc doesn't seem to be concerned, and dished pistons anyway.

For Corvette production aluminum cylinder heads. Compressed thickness is .051". This gasket's stainless steel fire rings prevent galvanic action between the aluminum head and cast iron block. (This gasket is used on 350 HO engines) (Can be used on cast iron or aluminum heads)

For the rest, water pump, fuel pump, carb, etc they seem like standard gaskets. Merc prices on these are not significatly overpriced.

 

[cobra 3.0]

Re: Merc VS GM Gaskets

Not sure about the above, but you can check Sierra or GLM for aftermarket marine parts prices. At least you will know that it is marine specific and the prices may be better than direct from a Mercury dealer.

 

[John_S]

Re: Merc VS GM Gaskets

Cobra, yea, I will be able to check NAPA for Siera parts. For 1st pass, I am trying to get the same gaskets, without paying significant premium.

 

[Buttanic]

Re: Merc VS GM Gaskets

Other than the riser and elbow gasket ( GM doesn't use water cooled manifolds ) all the other GM gaskets are fine or the Fel Pro aftermarket preformance gaskets. The one piece oil pan gasket is really good. NAPA also sell a stainless steel shim type head gasket if the compressed thickness of .016 doesn't raise compression too much but I believe that production GM engines come with the shim type gasket because it elimates the need to re torque head bolts during assembly.

 

[imported_rosco]

Re: Merc VS GM Gaskets

you can use an entire gm auto gasket kit with two exceptions. the head gaskets need to be for a marine application. the core is brass for corrosions reasons.

the other exception is the exhaust gasket set. you dont want to use the metal ones you get with a gasket kit. they will rust out in less than a year. header gaskets are ok, or any composite gasket. anything other than the asbestos / metal ones that come with an engine gasket kit.

the rest are absolutly the same. after market kits will work also for alot less money.

 

[John_S]

Re: Merc VS GM Gaskets

The original head gaskets were two layers of stainless steel sandwiched with unkown material. The part number that was stamped on them was not fully legable, but did not get a hit on GM part search, even on the partials.

I looked at some Sierra and Felpro gaskets sets. I did not find any specific marine set that will fit the vortec engine.

GM has a gasket set for Vortec (L31) engine. Part #12499223. The head gaskets included in the set are the #10105117 (.028 compressed) head gaskets. These are stainless and supposidly marine capable. I would guess that the exhaust gaskets were not marine compatable.

 

[Bondo]

Re: Merc VS GM Gaskets

I'd Think the the Exhaust Gaskets, at the Head, would be Fine if they're Composites,......

The Risers would be Per Manufacturer of the Manifolds......

The Only Head Gaskets to stay away from would be the plain Steel Shim gaskets,.....
Again,... Any of the Quality Composites are Fine in a Boat motor......


Are you going to Measure your Piston to Valve Clearances,+ Shoot for the Golden .040 Quench,..??..??..........

 

[John_S]

Re: Merc VS GM Gaskets

Bondo, sorry missed your last post and the thread fell off the 1st page. :$

No, I am not going for the magic 0.040 quench. From what I can tell, Merc is nowhere near a "good" quench. What I want to make sure is that I match the same compression ratio, or within reason, as Merc stock vortec engines. ie, I want to make sure that I can still burn unleaded regular gas.

Now Merc advertises a 9.4:1 compresion ratio for vortec engine and 9:1 for "standard" head 350's. Well after finding low-compression pistons with my 76cc heads, I couldn't understand how you could get 9:1 compression. When I ran the numbers in a static compression calculator, I couldn't come close. Even if I use an ideal shim gasket thickness of 0.016, the compression ratio worked out to only 8.4:1. The actual gasket on my engine is a stainless/graphite compisition, which is probably at least 0.028 thick (8.24:1).

In my research to try to find out what gasket thickness was provided stock on the Merc vortec, found 0.051. This was found in Dennis's SBC Marine Perf book. That gasket thickness works out to only 8.83:1 compression ratio. But, it is about the same magnitude (0.6) off from the non-vortec engine.

Ideally, someone would validate Dennis's book on the vortec head thickness. It seems rather excessive, though. If it was 0.051, I would only consider going to 0.039 gasket for a 9:1 compression.

FWIW, the values I am using (outside of head gasket thickness) are below:

Bore: 4.00
Stroke: 3.48
Head Gasket Diameter: 4.005 (probabply on ideal side)
Chamber Volume: standard: 76cc, vortec 64cc
Piston: -12cc
Deck Clearance: 0.025 (not measured, but SBC standard?)