Compression Issues

[mangel83]

To all those teams who have changed the CR using aftermarket pistons.

We took the engine apart (Suzuki GSX-R600) and had the cylinders just a little deglazed since the engine it's kind of new (just 3000 miles on it), we increased the CR using aftermarket pistons, we installed new rings as well, we've been told that the engine had to be broken in for a while so it could reach it's optimun performance.

When we put the engine back on we measured compression and it was 90psi each cylinder, after that we started it, and had it idling in neutral for like 10 or 12 minutes, then we measured again and it was 120psi.

Are these levels normal for this type of engines with that kind of modifications done to them? Should we expect an increase in compression levels as we run the engine more and more?

Any info on this would be greatly apreciatted.

[mangel83]

To all those teams who have changed the CR using aftermarket pistons.

We took the engine apart (Suzuki GSX-R600) and had the cylinders just a little deglazed since the engine it's kind of new (just 3000 miles on it), we increased the CR using aftermarket pistons, we installed new rings as well, we've been told that the engine had to be broken in for a while so it could reach it's optimun performance.

When we put the engine back on we measured compression and it was 90psi each cylinder, after that we started it, and had it idling in neutral for like 10 or 12 minutes, then we measured again and it was 120psi.

Are these levels normal for this type of engines with that kind of modifications done to them? Should we expect an increase in compression levels as we run the engine more and more?

Any info on this would be greatly apreciatted.

[DaveC]

Yes, thats normal. It takes a while for the rings to wear into the cylinder bore. As far as break-in, I'd break it in just like your going to use it. If you baby the motor the cylinders may glaze before the rings break in all the way, leading to more blowby. Cessna and Lycoming recommend a hard break-in for their aircraft engines, check their websites for good break in procedure. Also, break-in using regular motor oil, not synthetic.

[Dan Deussen @ Weber Motor]

Manuel,

Suzuki uses Nikasil coatings on the cylinders. These engines do not benefit much from the typical break-in procedures, as the Nikasil is very hard and it does not scuff in as iron liners would. I would recommend doing a short break-in just to make sure that you put the engine back together correctly. Then run it under your normal operating conditions. The piston rings will break in over time and from what we have seen on our engines,a performance increase of 1-2% is reached after well over 20 hours of running.

If you have a dyno, put your engine on it and run it with regular oil for about an hour. If everything is okay, your engine is good to go in the car.

[Ryan Schoffer]

Question:

We have a f4i with some moderate scoring in the cylinders - is it best to get the block resleeved for the higher CR pistons, or can they be replated?

[KU_Racing]

replated?? are the f4i sleeves plated?

we just had them re-honed; of course, the scoring on ours was extrmemly slight

[Erich Ohlde]

<BLOCKQUOTE class="ip-ubbcode-quote"><div class="ip-ubbcode-quote-title">quote:</div><div class="ip-ubbcode-quote-content">Originally posted by KURacing:
replated?? are the f4i sleeves plated? </div></BLOCKQUOTE>

Yes the F4i's have Nikasil plating. If you bore them they are supposed to be replated! They are also not to be honed.

[TiTiKo]

Thanks for the answer, we'll run the motor in our dyno

[james17]

See, this is odd. We had a very notable sport bike builder aid us with engine work, new rings included. He told us to break the engine in as you would a performance car engine, go to 50% throttle quick and then let the engine wind it self down 5 times, then 75%, 85%, 90%, so on, he said this is what he has always done, I also know he did no plating on the bores, this is kinda funny.

[adrial]

James,

Are you talking about 50%, etc throttle openings just free revving or under load?

They are saying that there is a nikasil plating on the cylinders walls...not that it must be recoated.

[DaveC]

The technique James mentioned is under load, and the load should remain so more engine braking occurs after the acceleration.

Wiseco's instructions are to break the glaze before installing stock sized pistons. Oversize pistons would need to be bored and replated. One place quoted me $135 per bore to replate plus $55 per hole to bore, at that price it's time to ditch the motor if the cylinder wall scoring is bad.

[Cody the Genius]

You guys have nearly missed one of the biggest questions pertaining to ring break in, and that is which ring material to which cylinder wall. For each one of these the the break in procedure can vary quite greatly.

cast iron ring to ductile or cast iron bore or nickisil- Low load (15-20%) @ 45-6500 RPM is needed and approximately 25-30 hours of dyno time. The engine also needs to fully heat cycle a few times while varrying engine speed every 20-25 minutes. Basically just be nice. The iron combination is what you get from many production cars and street applications, particularly cheap. The nickisil likes a little longer to run in but the moral of the story is be nice ,but not free revving, and vary engine speed while givving it a long time to break in.

chrome ring to ductile iron-DO NOT LET IT IDLE. Chrome plated rings must be run in under a decent load (30-40%)@65-8500 RPM and taken all the way to heat soak and run in not letting it cool down. This is mainly due to the fact that the hard ring will rapidly glaze the cylinder wall if the scuffing (load) goes away. This does not mean drive it like you stole it out of the box but rather keep it under sustained load and allow full heat soak bcause it has to be warm to seat the rings. "Plasma-Moly" rings are even harder than chrome and need to take a little more load, but the benifit is that both of these offer awesome ring seal and are fully broken in around 8-10 hours.

chrome/moly on nickisil- This is one of the hardest combinations to do right because because both the ring and cylinder wall are very hard. For new rings there should be a 1/2-1 thou "hone" just to lightly open up the nickisil and return the crosshatch. Next you shuould wetsand the cylinder wall -LIGHLY- with 800-1000 grit, not to remove the cross hatch but simply to diminish it slightly as a pretty smooth wall is needed. Next you run it in the nearly the same as the chrome/ductile iron method but with a longer run in period and closer to 25-35% load @ 5-7000 RPM.


OK, now that I have written you an essay, assuming that you are running 12.5-13.5:1 CR you should be seeing numbers closer to 180-190 Psi. I don't think you realy have any problems yet if you only ran it for 15-20 as you most likely have alot of break in time to go.

Oh yeah and the revving the engine to break it in thing is just a way to put the engine under load to scuff the ring while it is in the car, or bike, or anything else with a manual transmission where you can use engine breaking. People mainly do his when they can't get their motor on a dyno and it works, just not as well.

A good to also make is that a good non-detergent oil is best used on break in as it will not instantly wash away all of the assembly lube. Synthetic oil or Slick 50 or STP should NEVER be used on break in as they can actually wet the metal causing near instantaneous cylinder glaze.

After all of this is said and done-don't ask us, call up your piston manufacturer and see what they think. Most of them have a ton of experience and hey, you did just give them a lot of money.