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Hello All

1988 Onan P220G Opposed Twin. S/N unknown. MFR date is stamped on the flyball cover. Electronic ignition. Awesome beast of an engine

I got this engine as a POS on Craigslist and rebuilt it from ground-up

End result of my build is that CYL 2 runs much hotter than CYL 1 by anywhere from 70F to 100F. The temp difference is more extreme just after start-up and for the next 6 minutes or so at idle. Beyond that timeline, the levels L-R level out a bit but still uneven by 40-50F, all of which is unnerving for me

I bought oversized rings for CYL 2 from OnanParts in hopes that I could close the ring gap to 0.003-0.008in per spec but that didn't work. Gap remains at about 0.013. So I put it back together and hoped for the best. The heat ratio on CYL2 vs CYL1 remains a mystery

What could be the causes of CYL 2 heating up?

How are you checking the temp? What is being used?

They are not going to be 100% the same temp. Especially when both cyls have different compression and blowby for example. Valves might not be sealing 100% and many other factors. Sounds as cyl 2 is getting less fuel than 1. Leaner is meaner was the old wordage. Intake ports are not identical.

slomo said:

How are you checking the temp? What is being used?

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slomo said:

How are you checking the temp? What is being used?

Click to expand...

Hi slomo. I am using an Infrared Thermometer. Even if it is not reading the exact temp, the differential is still accurate of course

slomo said:

They are not going to be 100% the same temp. Especially when both cyls have different compression and blowby for example. Valves might not be sealing 100% and many other factors. Sounds as cyl 2 is getting less fuel than 1. Leaner is meaner was the old wordage. Intake ports are not identical.

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Good point. I will check that the valves are seating properly

There is not one engine out there that multiple cyls run at the same temp. Go scan a V-8 and report back. And those mostly are injected supposed to be spraying the same volume of fuel and so on. Casting thicknesses and many more.......

slomo said:

There is not one engine out there that multiple cyls run at the same temp. Go scan a V-8 and report back. And those mostly are injected supposed to be spraying the same volume of fuel and so on. Casting thicknesses and many more.......

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I hear ya, slomo, and have considered the countless variables. Though an 80-100F variation seemed a bit excessive to me on a 782cc engine. The fact that you are saying this is normal, I will sleep much better LOL! Thanks again! - Ken

Don't think it's normal but we need some word to talk about it. Some carbs have 2 different main jet sizes. Like the ol' Nikki Six carbs I think that fit twin engines. You might have Chinese plugs or one not firing 100%. Many many variables.

Does your carb have two different main jet sizes?

Again the same with V-8's. One fuel pump and 8 injectors all rated the same fuel volume. Every cyl will have a different air/fuel ratio.

slomo said:

Don't think it's normal but we need some word to talk about it. Some carbs have 2 different main jet sizes. Like the ol' Nikki Six carbs I think that fit twin engines. You might have Chinese plugs or one not firing 100%. Many many variables.

Does your carb have two different main jet sizes?

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Hi slomo. I believe it has just one main jet. See pics. Plugs are Champion RS14YC