late 70's cross flow question...defects?

[Thumpbass]

I was talking to a guy who runs a local salvage yard/used motor place and was telling him about my 1979 100hp Johnson that recently burned a piston. He told me that he thought he had remembered there being a factory defect in some late 70's cross flows that was directly related to the pistons. He couldn't remember what year(s) had the defect but he said it may well have been the 79's (like my motor). He also said he thought that OMC sent out replacement parts at no charge for years up until about 10-15 years ago because people would run with the defected piston for years and not ever know it until it was catastrophic.
Has anyone heard of this? I've never read anything like this on this board..but there are a lot of posts, so may be I missed something.

 

[Walker]

Re: late 70's cross flow question...defects?

High ring pistons??? That's the only gripe I ever geard about any crossflows

 

[DHPMARINE]

Re: late 70's cross flow question...defects?

May be true,but I can't say I recall it.Actually there weren't too many years in the seventies that had 100
hp.

But the OMC V4 is a great engine.

DHP

 

[F_R]

Re: late 70's cross flow question...defects?

Burned pistons are caused by running too lean or with too much spark advance, or too low octane fuel, or wrong spark plugs, or all 4. Can happen with any year.

There were several service bulletins out in the early 1970s concerning the issue which resulted from the changes in gasoline at that time and instructions for modifying the engines to prevent it. I would hope that they had it fixed on motors from the factory by '79. But that doesn't help when the customer messes it up.

 

[Dhadley]

Re: late 70's cross flow question...defects?

Actually there's nothing wrong with the old high ring pistons if the motor is set up right. Hot rod guys still look for and use them. They used them for years and when the lead (coolant) was taken out of the fuel, combustion temps became critical. That's when we learned all about coking.

 

[Thumpbass]

Re: late 70's cross flow question...defects?

Burned pistons are caused by running too lean or with too much spark advance, or too low octane fuel, or wrong spark plugs, or all 4. Can happen with any year.

There were several service bulletins out in the early 1970s concerning the issue which resulted from the changes in gasoline at that time and instructions for modifying the engines to prevent it. I would hope that they had it fixed on motors from the factory by '79. But that doesn't help when the customer messes it up.

may be I used the wrong terminology...I actually didn't "burn" a piston, the ring(s) broke and roughed up the piston, head and cylinder.

 

[Dhadley]

Re: late 70's cross flow question...defects?

That's caused buy lugging the motor. When we had lead in the fuel for a coolant it wasn't an issue. Once we "got the lead out" it was an issue.