New Rings Installed--When to check compression?

After doing a top-end overhaul, including installing new rings, when is a good time to do a compression test?

The reason I ask is that I've only got about 15 miles on my engine since getting it back together, and about 15-30 minutes of idle time while I made adjustments. Last night, with the engine warmed up, I decided to test compression.

I took all the plugs out, throttle open, and cranked for a few seconds. I was surprised to see that I am only getting about 70psi in each cylinder.

It seems to be running well, and it has plenty of power when riding.

Is it too early for me to be testing compression? Do I need to put more miles on it so the rings get better seated?

Or, since it is running well, is it more likely that my el-cheapo Harbor Freight compression guage is not reading correctly?

I could do a leakdown test, but before I get setup for that, I wanted to know if I should put more miles on it before worrying about compression readings?

The concensus is to run it as hard as you plan on riding it to seat the rings properly.

In other words, don't "baby" it because you're afraid of breaking something. Obviously pegging it into the redline isn't recommended. :whistle:

Running well and plenty of power while riding do not go along with 70 psi of compression. I don't know if it would even start with only 70 psi.

Try a different gauge.

steell wrote:

Running well and plenty of power while riding do not go along with 70 psi of compression. I don't know if it would even start with only 70 psi.

Try a different gauge.

Man I don't know about that 'not running'. The REI (Royal Enfield India) bikes only make 6.5:1 in a thumper and run just fine on fermented elephant dung, even up in the Himalayas where the air is so thin that the 6.5:1 is only making like 50psi inside the jug.

Seriously, they are only 6.5:1 CR, AFTER the rings seat.

Post edited by: Duck, at: 2007/02/14 20:33

You will just get your blood pressure up if you start checking compression early. Wait for 500 miles at varied engine speeds. Change the oil/filter at that point to clean the crud left over from the rebuild and check compression at that point. The bike will run @ 70 PSI but won't be a barn burner. If you have someone else local, who owns a compression gauge, you might want to borrow it and compare the readings to your own when you do recheck the compression. Did you do any valve work? Clean up? Lap? Anyway, I think 15 miles won't see the rings seat.

Did you have the cylinders bored out and/or honed while doing the top end rebuild???? I can't see why you would not have a 100 psi plus right away and then a increase in pressure as the engine wears in. Please provide some more info...

1045

To answer the questions asked:

WG, yes I did do a valve job.

1045, yes I did hone the cyls.

Right now, I'm thinking my pressure guage is faulty. It seems to run well and ride strong. I doubt that 70psi would do that. I'll ride it for a while longer before trying again, and I'll borrow a friend's guage.

Thanks guys.

Skyman wrote:

To answer the questions asked:

WG, yes I did do a valve job.

1045, yes I did hone the cyls.

Right now, I'm thinking my pressure guage is faulty. It seems to run well and ride strong. I doubt that 70psi would do that. I'll ride it for a while longer before trying again, and I'll borrow a friend's guage.

Thanks guys.

did you remember to turn it over 4 times?

After installing a big bore kit on my 650 my compression was only 80 psi. It slowly got better as it broke in. After about 800 miles it now has 170 psi.
Wiredgeorge is correct don't check the compression until after break in utherwise it will drive you crazy. If it runs then break in it hard, put on about 1000 miles then check it.
I have engines run on as low as 50 psi.

themachine wrote:
did you remember to turn it over 4 times?[/quote]

Yep.

baldy110 wrote:

After installing a big bore kit on my 650 my compression was only 80 psi. It slowly got better as it broke in. After about 800 miles it now has 170 psi.
Wiredgeorge is correct don't check the compression until after break in utherwise it will drive you crazy. If it runs then break in it hard, put on about 1000 miles then check it.
I have engines run on as low as 50 psi.

Okay, thanks.

baldy110 wrote:

After installing a big bore kit on my 650 my compression was only 80 psi. It slowly got better as it broke in. After about 800 miles it now has 170 psi.
Wiredgeorge is correct don't check the compression until after break in utherwise it will drive you crazy. If it runs then break in it hard, put on about 1000 miles then check it.
I have engines run on as low as 50 psi.

Just out of curiosity, how easy did it start with only 50 psi of compression??