New Rings Installed--When to check compression?

Actually that engine started and ran pretty good, just didn't have any power.
The old Ford Model T had only 5-1 compression with about 70 psi compression when new and those ran fine.

wiredgeorge wrote:

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.

I agree that 15 miles won't set the rings. Definitely check it with another guage. If that one agrees or is anywhere near close to the same reading, then double check valve clearances.

That's a really low PSI, even for only 15 miles on the ring job.

Did you soap and water the block with hot water and a good brush, followed by an oil wipe until all traces of black on a clean white rag were no longer appearing?

Post edited by: larrycavan, at: 2007/02/17 19:47

baldy110 wrote:

Actually that engine started and ran pretty good, just didn't have any power.
The old Ford Model T had only 5-1 compression with about 70 psi compression when new and those ran fine.

how about a Model A?

I have a 79 1000 ltd project. It had set for a long time inside. When I got it started it run fine but just in the garage. It is not ready for the street. I checked the comp and it was a perfect 75lbs in all cyl. I was told by some mech. That in those years some low compression motors were made.. don't have a clue if he is right or what is right. It is just odd that they are so consistant

larrycavan wrote:

Did you soap and water the block with hot water and a good brush, followed by an oil wipe until all traces of black on a clean white rag were no longer appearing?

Larry, I did wash it with soap and water, but didn't give it the "white glove" test. :blink:

I also did wipe the cyls with oil before installing.

I dunno. I'm thinking my compression guage is off. It's running really well. I took it out yesterday to do the break-in proceedure described here: www.dansmc.com/engine_breakin.htm

I found a long, flat, country road with no traffic. In second gear, I accelerated with WOT to 7500 RPMs, then let it coast back to 2000 RPMs. I repeated this about a dozen times.

The acceleration was downright scary.
:woohoo: :woohoo: :woohoo:

I had to lean way forward because it felt like the front was going to come off the ground at any moment. :ohmy:

Afterwards, I went home, picked up my wife, and we went for a nice two-hour ride. I'm not going to worry about compression for now. It's riding really nice. Who cares if it's really only getting 70psi. The main thing is that it isn't acting like 70psi.

rgpbeme wrote:

I have a 79 1000 ltd project. It had set for a long time inside. When I got it started it run fine but just in the garage. It is not ready for the street. I checked the comp and it was a perfect 75lbs in all cyl. I was told by some mech. That in those years some low compression motors were made.. don't have a clue if he is right or what is right. It is just odd that they are so consistant

Agree it seems odd the low psi readings are so consistent. Might first re-check compression figures with a different gauge to confirm the readings. Also re-test after putting a teaspoon of motor oil into the cylinder combustion chamber through the spark plug holes. Increased compression (after oil added) points to rings. No change in compression (after oil added) points to valve clearance or valve malfunction.

Perhaps piston rings have become stuck in their groves from sitting so long. This condition may have been aggravated where fuel had leaked into the combustion chamber.

One cheap easy long shot effort might be to squirt some PJBlaster in each spark plug hole every day for a week hoping it will work down into the ring grooves and free them up. Believe Yamaha offers an oil designed for this particular purpose -- but have never tried it.

FSM says standard compression with hot engine is 128-156 psi with minimum service limit of 100 psi, and less than 14 psi difference between cylinders.

Don't know about any "low compression motors" having been made, unless reference was possibly to lower compression turbo engines.

Would suggest, if not already done, changing the oil and filter before doing much more test running.

Skyman wrote:

larrycavan wrote:

Did you soap and water the block with hot water and a good brush, followed by an oil wipe until all traces of black on a clean white rag were no longer appearing?

Larry, I did wash it with soap and water, but didn't give it the "white glove" test. :blink:

I also did wipe the cyls with oil before installing.

I dunno. I'm thinking my compression guage is off. It's running really well. I took it out yesterday to do the break-in proceedure described here: www.dansmc.com/engine_breakin.htm

I found a long, flat, country road with no traffic. In second gear, I accelerated with WOT to 7500 RPMs, then let it coast back to 2000 RPMs. I repeated this about a dozen times.

The acceleration was downright scary.
:woohoo: :woohoo: :woohoo:

I had to lean way forward because it felt like the front was going to come off the ground at any moment. :ohmy:

Afterwards, I went home, picked up my wife, and we went for a nice two-hour ride. I'm not going to worry about compression for now. It's riding really nice. Who cares if it's really only getting 70psi. The main thing is that it isn't acting like 70psi.

I'd be willing to bet your guage is inaccurate.

There's a procedure that I've done for many, many years with block prep. Wiseco included instructions with their piston kits and it's always worked great for me. Check wiseco's web site, it might be on there. It's the same as I described previously.

I do have 160-165 psi with a cold engine. Its a stock Kz1000 with only 1200 cc, did run 200 miles since bore and I do have speed knock problems when pulling the throtthle. So the opposite, anyone a solution??

martijn wrote:

I do have 160-165 psi with a cold engine. Its a stock Kz1000 with only 1200 cc, did run 200 miles since bore and I do have speed knock problems when pulling the throtthle. So the opposite, anyone a solution??

Are we talking stock everything except resleeved and bored to 1200cc?

Details are needed.

In the meanwhile you could back your timing off 3 degrees and see if it helps. That's not abnormally high compression numbers. You may be lean on the needle and main jet as well.

themachine wrote:

did you remember to turn it over 4 times?[/quote]
What is this all about ?

mark1122 wrote:

themachine wrote:

did you remember to turn it over 4 times?
What is this all about ?

I'm sure he meant that when doing a compression test, you should turn over the engine at least 4 times (cycles) to give enough time for the pressure to build to its peak.

Post edited by: Skyman, at: 2007/02/20 00:21

I thought I would come back and revisit this thread, now that several months and about 1700 miles have passed since rebuild.

The compression readings have come up some, but not nearly as much as I had hoped. Currently, I get about 95-100 PSI on each cylinder. It starts easily and runs well. Doesn't seem be be really lacking in power, though I've never ridden any other KZ1000s, so I don't really have anything to compare with.

I did a leakdown test, and I'm getting about 15-20% leakage past the pistons (air coming out the crankcase). Very frustrating.

Since it's the middle of riding season, and the bike is running well enough, I'm not inclined to do a major teardown now. I'll ride it until late fall and open the engine up then and see what's going on.

When I installed the new rings in February, I did my best to measure the cyls and ring gaps and all that, and it seemed like everything was within spec. But I must have missed something. Maybe the cyls were ovaled, and I didn't catch it.

I'm having a blast riding it. But the perfectionist in me hates knowing that my compression readings are below standard. Arrrgh!

So what am I missing out on with low cyl pressure? If my readings were in the 150psi range, would I likely notice a lot more power?