Omc 6-8

[Playboy]

What is the difference in the cylinderblock on theese engines.
Seems to be different partnumber.

 

[oldcatamount]

Re: Omc 6-8

When you say "6-8" do you mean 6 horsepower and 8 horsepower? If so, the only major difference is in the cylinder bore diameter and stroke length.

 

[Vic.S]

Re: Omc 6-8

IIRC the mid 1980 ones ( like my 6 hp) have the same bore and stroke. I think the difference is in the porting. Inlet manifolds are different too IIRC. Just about everything else, except maybe carb jets, is the same

 

[Chinewalker]

Re: Omc 6-8

The 1980s era 6 & 8hp models have different crankcases and intake manifolds. The 6hp has 3 reeds per cylinder, while the 8hp has 4 reeds per cylinder. Not easy to convert one to the other - unless you have an 8hp to borrow from. If that's the case, take the 6hp cowling, put it on the 8hp and you're done...

 

[Playboy]

Re: Omc 6-8

Yes. I meant 6 and 8 hp. from 90ies.

The blocks look identical as well as the porting. Both share the same reeds and manifolds, can?t figure what the difference may be or could it be the compression only?

 

[Chinewalker]

Re: Omc 6-8

The cylinder block and crankcase part numbers are different for the 6 and 8 (.ie, 1994 model year, 6hp Cyl. & CC is #433929, 8hp is 433930.) Carbs get different part numbers, too. They share the same head and pistons, so the compression is the same...

More than likely, the porting is different on the blocks...

 

[Playboy]

Re: Omc 6-8

The cylinder block and crankcase part numbers are different for the 6 and 8 (.ie, 1994 model year, 6hp Cyl. & CC is #433929, 8hp is 433930.) Carbs get different part numbers, too. They share the same head and pistons, so the compression is the same...

More than likely, the porting is different on the blocks...

I had a closer look at the porting on the 6 hp. the porting is quite porty with big
holes, I can?t understan how it could be changed to 8 hp by modifying them considering that the ports are so high as they can be drilled on an serial production engine.
What if the case is planned? Where can I get reliable compresson figures for both?

 

[Playboy]

Re: Omc 6-8

I had a closer look at the porting on the 6 hp. the porting is quite porty with big
holes, I can?t understan how it could be changed to 8 hp by modifying them considering that the ports are so high as they can be drilled on an serial production engine.
What if the case is planned? Where can I get reliable compresson figures for both?

By the way, the compression is 80 PSI (quite low) on the 6 hp.