30psi compression loss in all four cylinders

[turborebel]

With five miles on rebuild I had 198, 198, 192, 188.
A second test 50 miles later was 194, 194, 197, 186.
Know with 500 miles on the rebuilt motor I have 160, 162, 162, 158.
The engine builder says it could be a loss of ring tension.
The guy at Wiseco thinks it might have been fuel wash.
I did log knock more than once at only 10 or 12psi of boost.
Instead of backing off the timing I added fuel and the wideband read 10 more than once. I have a new set of rings, but who knows if they will seat well at 600 miles.
So what happend and what can be done to bring compression back to 195 without honeing the cylinders?

Thanks for any advice,



brent.

 

[tkelly27]

You could easily have not been looking and gotten into conditions where you could have had ring wash. You really shouldn't mess around with tuning while breaking in a brand new engine. That is, you should have a decent tune you know will run for a while when you are breaking in a new engine. Even if you have to buy octane booster and unhook your wastegate! However 10 is not an engine killing AFR IMO, but a few pings... I dunno.

Anyways, it's to late now. Those numbers don't sound low to me. If you look at it, I'd much rather have the 160's with 4 away from each other than the 190's within 10 of each other. It also got progressively lower from the 0 miles to the 50 miles. You should have tried @ 100 and 200, etc.

Other than the small amount of detonation and semi rich, did you break it in properly? How does it run? Have you tried putting oil in the cylinders during a test and seeing if that helps out any? Leak down test? What compression ratio did you go with to help figure out if those numbers are low, or on target?

So if you've actually gone and f*ed up your compression, while I've never tried it in a turbo car, restore did actually help me pick up some psi and even out the cylinders in a car with 250k miles. Again, I've never heard of it doing good things for turbo cars, and I've never heard of it doing bad things. Please, please, please! figure out if you've actually got a problem before dumping the blue stuff in there.

You know what would be cool? If they had compression raising/lower spark plugs. They'd thread in deeper or shallower into the combustion chamber. Maybe they make those already, wtf do I know...

 

[Burnett03]

You know what would be cool? If they had compression raising/lower spark plugs. They'd thread in deeper or shallower into the combustion chamber. Maybe they make those already, wtf do I know...

horrible idea.. do some more reading on engines and compression ratio

 

[turborebel]

I did the oil test on the #1 cylinder. The first reading was 250psi. I waited a few minutes and cranked the engine without anything in the spark plug hole. The second test showed 225psi. A third test was done after waiting a while and showed another 225psi reading. I have 9:1 pistons so it should have at least 180psi if things are right. The car runs stong but it's burning oil. It's not enough to see from the tail pipe, but the dipstick is showing oil loss. I don't feel like reringing, but I would if knew it would make the compression go back up to where it should be. If it was not for the oil loss I might not be so concerned.

 

[dsm-onster]

Are you sure you've done your compression check correctly? Fitting threaded prperly and tightly. Also, engine must be rather warm when doing a basic check. It just looks like to me you did a check while warm then another while cold. . .

Slight oil burning is normal early in the break-in. Chrome/moly or iron. If chrome/moly was used break-in takes significantly longer...

 

[turborebel]

Unfortunately the engine was at full operating temp. 190 degrees. I've done the test several times with very consistent results. I also found that if I tested right after shutting off the engine and then waiting a few minutes the compression would be higher by 10 or 15psi on the second test.

 

[tkelly27]

http://www.custompistols.com/cars/articles/compression.htm

"The wet compression check will, in most cases, be higher than the dry compression check. This is because the oil creates a better seal against the top of the piston rings and the cylinder bore. The LOWER the difference in readings between the dry and wet checks, the better the condition of the bores and rings."

I don't know that guy from Adam, but that was the first thing that popped up from a google search.

That's a 90psi difference between wet and dry, more than 50% of the dry CR. I think you've got problems.

It would make sense right after running to have higher compression because there should still be a bit of oil on the cylinder walls.

Unless you've got a super huge cam that we don't know about, or you reused a thrashed head. The oil burning also bothers me. You're not really in early break in anymore.



I dunno how you got to be a proven member replying to threads without adding any useful information at all like that. You've got a PM, as I'd rather this be about helping the orignial poster than the definition of compression ratio.

 

[turborebel]

I agree that there is a problem, but can it be fixed with new rings, but without rehoneing?

 

[tkelly27]

I've never tried it, but I know there are both the ball hones and the stone type hones that people use. None are as good as a machine shop IMO, but there are many cars running with their cylinders honed by them.

Here is an example of the stone version
http://cgi.ebay.com/ebaymotors/HD-3...tegoryZ43993QQihZ015QQitemZ250101037115QQrdZ1
Here is an example of the ball style
http://cgi.ebay.com/ebaymotors/SBC-...020QQitemZ300085966096QQrdZ1QQsspagenameZWD1V

Which one is best? You're going to have to ask google.

Are you planning on leaving the engine in the car? If so, PM me, I've got a TON of questions for you!

Also, for when you get it back together, here is a pretty technical explanation of how and why motorcycle racers break in their engines
http://www.ntnoa.org/enginebreakin.htm
It makes a lot of sense.

Finally, I'm not a short block expert and can't say for sure that you've ruled it down to the rings. It sure as hell looks like it to me, and we're running out of options, but I've been wrong before. I'd definitely wait for some second opinions before ripping it apart again.

 

[turborebel]

Thank you for the links and advice. A sales rep. from Wiseco said that the nitrided steel rings would have much a better chance of seating than iron or chrome rings. He also made it sound like hoening the block in the car was bad idea and sould be avioded.
What are my chances of seating these rings in a block with 600 miles?

 

[oldman]

How did you break in the motor?

 

[turborebel]

Somewhat like the motoman break-in, but without going over 4500 RPM for the first 100 miles. Hard acceleration and engine breaking.

 

[oldman]

Somewhat like the motoman break-in, but without going over 4500 RPM for the first 100 miles. Hard acceleration and engine breaking.

Well, then what is the point? The most important part of the motoman method is the first 50 miles and taking it up and down the entire rpm range.

 

[turborebel]

It was my understanding that the pressure of combustion pressing the rings against the cylinder walls was the main goal. That, along with the vacuum of the engine braking to keep the rings and ring lands clean. I don't unerstand how would it help to rev through the entire RPM range. Would you recommend rehone in my case?

 

[oldman]

It was my understanding that the pressure of combustion pressing the rings against the cylinder walls was the main goal. That, along with the vacuum of the engine braking to keep the rings and ring lands clean. I don't unerstand how would it help to rev through the entire RPM range. Would you recommend rehone in my case?

Well your wet test indicates ring seal issues, whether this is caused by break in method, running pig rich during break in or other issues is hard to tell. I would first resolve your possible tuning issues and give it more break in time. If things don't improve, I would bring it back to the builder and hold him responsible.

 

[turborebel]

The engine builder has agreed to rehone for free. I'm not looking forward too taking the engine out and apart and then putting it all back together, after a total only of 609 miles. I am still leaning towards just dropping the oil pan, taking off the head, taking out the rods and pistons, reinging and putting it back together. Please tell me if this is a really bad idea. What are the odds that my compression will go up or down? The salesman at Wiseco said the milage limt for reringing with the steel rings was 2,000 miles. My engine builder seems less optimistic. What do you think will happen?

 

[tkelly27]

I would talk to your engine builder and see what they suggest. If what I was reading was correct, the point of the break in is to take off the peaks that the hone has created.

"If the rings aren't forced against the walls soon enough, they'll use up the roughness before they fully seat. Once that happens there is no solution but to re hone the cylinders, install new rings and start over again."
From the motoman's mouth.

I don't think the rings would ever be allowed to wear properly by putting it in without any kind of a hone.

I agree, before pulling it out and doing it again, you want to get your tune at a place where you won't need to change it, you'll want to disconnect your WG flapper.

Now may also be a good time to consider experimenting with oil additives to see if they do anything at all, or if they are just snake oil. You're going to have to pull the engine apart one way or another, how stoked would you be if it temporarily fixed it? Personally, I would try it, but then again I'm a little nuts and have "horrible ideas" and need to "do some more reading" about what exactly compression ratio is... To think, all this time it was just an ity bitty fraction.

 

[motomattxxx]

Remember that the "motoman" method is for breaking in two stroke dirt bikes and not four stroke automobiles, thus the name "moto" man. The whole theory on the "motoman" method is bunk and now you have found out the hard way have'nt you? This is no good, and I hope that things look up for you. I strongly suggest that you ask your machinist how to break the engine in this time and take his advice since he is the one that will be fixing things if they are'nt right anyway. What kind of oil did you use for breakin? hopefully it was non synthetic, if not then that can be another reason for the unsuccessful ring seating.

 

[turborebel]

Thanks for all your help. I'm going to run with what I've got for right now. How many miles are recomended before nitros oxide can be used?