Mercruiser 3.0 135hp. Crank and rods

[Bow4game]

With compression that high there is liquid in the cylinder. Head is warped so gasket is not sealing or cylinder is cracked and water is leaking in.

When the motor diesels, that's when motor runs in reverse just before it dies and sucks in water. The water can bend rods and break things

The bearing journals are not parallel and flat. Your machine shop stuck it to you pretty good

Right now I would suggest find a shop to do a total rebuild which can be verified it can do the job, or buy a reman from a place like Michigan motors

No evidence of water. I just pulled it apart. If I put timing to zero it won’t diesel. When I shut off. The compression test is probably not accurate. I agree super high. The mains all look good. That’s a plus I guess ha.

 

[Scott Danforth]

It was not a gm. It’s an aftermarket 3.0. It has a scat crank in it. Not sure on the manufacture.

scat doesnt make a crank for a GM 3.0

if you dont believe me, here is there offerings https://www.scatcrankshafts.com/about-crankshafts/crankshafts-product-search/

 

[Bow4game]

your crank needs to be reground or replaced.

Well that’s what I though lol. He said it will just hold oil be good to go! And here I am again. You are right though I don’t think he ground my crank flat! Holding up the bearing on back side shows daylight and a Little Rocking action.

 

[Bow4game]

scat doesnt make a crank for a GM 3.0

if you dont believe me, here is there offerings https://www.scatcrankshafts.com/about-crankshafts/crankshafts-product-search/

 

[Bow4game]

Scat 19215. Idk what to tell ya.

 

[Bow4game]

Scat 19215. Idk what to tell ya.

Maybe they just started idk. I couldn’t find nothing on it also. But it’s stamped

 

[Scott06]

Bearing clearance or connecting rod big end out of round causes that . If you can’t find someone local who is comment machine shop wise buy from somebody like Michigan motorz. New base engines are about$3800, reman are like $2400.
you can save some getting yours rebuilt just needs to have somebody who can go through, correctly measure and figure out what fitment mismatch u have

 

[Bow4game]

Okay took it new machine shop. Crank is getting ground and checked. Found the problem we believe. Two of the rods was not very round. I’m gonna be ordering my kit once I find out the bearings sizes. My question is concerning the piston. Should I keep the pistons that came with the motor. They are 10.5 to 1 or Should I order some flat top pistons that are more like what’s in the marine application? I would like to run 87. So do I change pistons or just pull the timing and use high compression? Thanks again guys. I added a pic of what pistons look like.

 

[matt167]

You can't pull enough timing to prevent detonation with 10.5:1 on regular in an iron engine. Possibly can do it on a raw water boat motor where they typically run colder but it still does not add up good IMO.

So this was a new reman engine and the rods were not re sized to the new crank.. Machine it correctly, make sure the rods and mains are true with a dial bore gauge which sounds like you have a good shop, and then it'll run good.

 

[Rick Stephens]

I'd be running the stock piston type. Not sure why anyone would put a higher compression piston in an industrial motor.

 

[Scott06]

I'd be running the stock piston type. Not sure why anyone would put a higher compression piston in an industrial motor

sage advice. Keep it to 9.0 or 9.5 to 1 and you can live on 87 octane. You may be able to mill the dome off the aftermarket pistons. Your machinist would know the options

 

[Bow4game]

You can't pull enough timing to prevent detonation with 10.5:1 on regular in an iron engine. Possibly can do it on a raw water boat motor where they typically run colder but it still does not add up good IMO.

So this was a new reman engine and the rods were not re sized to the new crank.. Machine it correctly, make sure the rods and mains are true with a dial bore gauge which sounds like you have a good shop, and then it'll run good.

Okay that’s good advice and well noted thank you. Thanks guys I’ll swap the pistons back to flat tops or ask him about milling them flat.

 

[Bow4game]

I'd be running the stock piston type. Not sure why anyone would put a higher compression piston in an industrial motor.

Only thing I could think of is maybe natural gas requires higher compression? Or maybe propane.

 

[Rick Stephens]

Been too many years since even discussing how to set up a motor for propane. A quick search says that may be your answer. LPG has high octane but lower energy than gasoline. Upping compression will equal the mileage that the typical low octane 8.5:1 automotive engine got when converting to LPG. Of course, the 3.0L never got used in autos.