Will fresh rings and hone mess with compression?

[SXR-FOREVER]

Will fresh rings on a fresh hone give accurate compression or do you need to wait until after the motor has broken in and the rings are seated to get the actual compression ratio?

If this is a 'nube question forgive me but I had to ask..

Trevor

 

[rollin5150]

In my experience, you have to "seat" the rings to get a more accurate reading with a compression gauge.

 

[Waternut]

Generally if you haven't run the engine yet, you'll notice an increase in compression after it's assembled due to all the oil used during assembly. My last rebuild dropped about 20 psi in each cylinder after it had been run lightly for the first time. I asked the same thing when I reassembled my engine and my 35cc domes were producing over 200psi.

 

[SQUARE JOEL!!!]

Will fresh rings on a fresh hone give accurate compression or do you need to wait until after the motor has broken in and the rings are seated to get the actual compression ratio?

If this is a 'nube question forgive me but I had to ask..

Trevor

A gauge will only give you the pressure. Compression ratio is a calculation of several factors

 

[SXR-FOREVER]

Ah sorry, I meant compression pressure.

So it may be different after the break in but will it show accurately if the compression is even between the two cylinders before the rings seat?

 

[Waternut]

It won't be perfect but if they're close, I'd call it a fudge factor. If one was 200psi and the other was 170-180psi immediately after assembly, that might throw some red flags in my head. I think mine were about 5-7 psi off after assembly and after the first ride but the difference isn't as much now.

 

[surferdude345]

Of most of the motors i have built - first reading is high because of oil used to assemble - after assembly lube is burned its lower then when its broken it / seated about a tank or so it is what it gonna stay. so your really not gonna get the right reading till rings are seated - a snap on type gauge is the only way to get the best reading

 

[SQUARE JOEL!!!]

Agreed that a higher end gauge is best but as long as you're running relatively normal compression and are sure you are using the correct octane fuel then it's not the highest readings that really matter. The concern is the difference in readings between the cylinders, any gauge can give you that.

 

[chriselmore_1]

on my latest build my comp was off about 15 psi per hole. i freaked out bought new rings gaskets and got ready to tear everything apart. everyone told me to shut up and run it. everything evened out after the break in. 1-2 psi difference in holes now