broken pistons

40ford · Jul 10, 2018

I've used this 8N of mine for several years. Other than tune ups, I have never touched the engine. Lately, after a long run cutting grass, it started making a louod tapping sound. I'd stop and the next time everything was fine. The other day, it got bad so I stopped and decided it was either a rod bearing or something major like that. I pulled the pan and the bearings looked fine. I pulled the head and found that all 4 pistons were broken! Many rings broken - a mess. See the photos. What are those pistons with the strange raised lump on the top? What caused this much damage? And why did it run so good all this time??

JerryCPP(WA) · Jul 10, 2018

I don't know about the lumps - they may be high altitude/high compression pistons. Starting fluid, if you're not using the premium stuff, will break rings, and once the rings are broken the pistons can also fail.

Roger in Iowa · Jul 10, 2018

The raised lump can be high compression pistons that were available from TSC. I had them installed in a 9N direct in the block without sleeves.

Are you running 91 octane fuel? You probably should have been with those pistons.

WayneIA · Jul 10, 2018

Are these four ring pistons?

40ford · Jul 10, 2018

Yes. I never used starter fluid and been using non-ethanol hi test for the last few years when it became available in my area. This answers the other comments. Thanks guys.

WayneIA · Jul 10, 2018

4 ring pistons have two oil control rings. That is one too many. They run too dry. Three rings on a four ring piston works just fine.

Roger in Iowa · Jul 10, 2018

timing too far advanced causing detonation??

Can you post pictures of the piston tops?

40ford · Jul 10, 2018

Don't think the timing is off. Front distributor and timed on a KR Wilson timing fixture. Never heard any detonation sounds. Who knows. It's an old girl and I've used it a LOT in the 20 years or so I've had it. It owes me nothing. I've got new pistons and rings. If the temp would go below 90 for a few days, I'll get it done. And I'm in New York State!

The photo of a piston top is about typical of what they all look like.

agjim · Jul 11, 2018

I also have a 2N with high compression pistons running in the block without sleeves. I left the bottom rings off the pistons like WayneIA mentioned. It works fine.
Jim

Dean · Jul 11, 2018

Look for evidence of compression domes contacting cylinder head.

Dean

40ford · Jul 11, 2018

Not a mark on the head's combustion chambers.

Roger in Iowa · Jul 12, 2018

For all four to fail, there has to be some common denominator. Such as low grade fuel, timing, overheating, carb settings,, etc??

Would not think being 4 ring would have anything to due with failure after all these years, if they were four ring???

Roger in Iowa · Jul 12, 2018

When was the distributor off and timing sent? Recently?

broken pistons

40ford

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