Compression readings on a 99 Dominator...

Can anyone tell me what the compression reading should be roughly on a reconditioned 600cc Dominator engine after bedding in...? Cheers.

You seem like such a jackwad I imagine no one will really respond.
You remind me of our dear departed Norluck.
Maybe you are him in drag...

Either way.....It's been nice not knowing you.........

Dang. That was abrupt. Maybe the recent horror show on the Commando page has folks understandably on edge about your user name. You may find the folks willing to tag you are limited. You may or may not care.

There's a lot going on to determine a reasonable range of acceptability, but 99s were not particularly sporty.

How long ago was it reconditioned?

Stock, relatively low compression pistons?

Stock, relatively soft cam?

Depending on the answers to those questions, I'd be happy with anything above 125psi, ok with anything above 100 psi, and bummed with anything below. A leakdown test would be a good follow up to a compression test for more insight into the wear and health.

Checked dry and compression was 100 on one, 80 on the other (dry test). Checked our other 600 and it was 165 on both dry, 180+ when we added oil. Would this be normal for the 2nd engine or would hi compression pistons be needed to achieve these figures?

I would estimate that you might need 8:1 compression ratio to see over 180 psi on a compression test. If your inlet valve closes very early or very late, then my estimate is wrong.

Cold compression tests don’t mean much, but 80 psi is very low. Run the engine for a while and repeat the compression test.

Triton Thrasher said:

I would estimate that you might need 8:1 compression ratio to see over 180 psi on a compression test. If your inlet valve closes very early or very late, then my estimate is wrong.

Cold compression tests don’t mean much, but 80 psi is very low. Run the engine for a while and repeat the compression test.

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I compared both engines cold for the comparison.

Fuckthetrolls said:

Checked dry and compression was 100 on one, 80 on the other (dry test). Checked our other 600 and it was 165 on both dry, 180+ when we added oil. Would this be normal for the 2nd engine or would hi compression pistons be needed to achieve these figures?

Click to expand...

180 would be higher than expected, but again, there's a lot of factors, like how much oil you added.

160 would be great, but like TT said, hot readings are worth more than cold, even as an apples to apples reading. The 80 pot might tighten up to an acceptable range, but that's low.

A leakdown test would say more.

Going to take the barrels off it to check. I've a suspicion that someone has fitted fitted possibly new pistons or rings without honing the barrels.