Bad compression after rebuild

[GSX_Dan]

I just had a engine builder install Wiseco 9:1 .020" overzised pistons/rings and I'm getting weird compression numbers. They are 145-105-175-165 after 800km. I did a wet test and leakdown test to find the root of the problem. It seems to be the rings not sealing properly since the cr goes up to 210psi when I perform the wet test(even cyl#2). The boring/honing and piston/ring install was all done by a reputable machine shop and he checked the ring endgaps which were .014 to .016. He said this was within spec, but I didn't get a spec sheet with the Wiseco piston/ring box so I don't know what he went by. I know the compression is supposed to be around 192psi and I'm not even coming close to that. I do not have any experience with rebuilding engines, this is my first rebuild and I am very dissapointed. What are some things I could check for if I removed the head, and possibly pistons. I would like to find the cause myself before I bring it back to him just in case he might try to cover up a mistake.

 

[chad92turbo]

i had the same prob just found out today what it was, one of my brand new lifters was bad, try changing your lifters and see if it helps. this is just a quick "see if it works" fix thought it might save u the trouble of pulling the head hope i was of some help.


ps the lifters arent cheap so if u have acces o some known good ones id try them b4 u bought a new set

 

[kessler]

Well i had some of the same problems in this area myself but over a little bit of break in time and also i hope your not running an synthetic oil right now cuz that will prevent the rings from setting corectly but ill have to agree check your lifters. Did you put the head back on ( i mean like put the lifters,followers,cams back in your self or did you have the other guy do it?) the reason i ask is if you dont compress the lifters before reinstalling them your going to have these problems.

Sorry if this didnt help but its just some things you might want to check on...

 

[GSX_Dan]

I assembled the lifters/cams/rockers. The lifters were throrougly cleaned via the faq's, and I installed the shim underneath that's needed with my regrind 264's. I also installed them dry without any oil. They were noise for the first 15 minutes but then they settled in and there is no lifter noise now.

I don't see that being my problem since I narrowed it down to the rings via the wet test. I appreciate all the info I can get though, thanks.

 

[pneumo]

What type of driving did you do to break in the motor?

 

[boostedinaz]

Alot of problems I have heard of liek this is becasue the builder didnt use a torque plate when boring the block. I guess not alot of machine shops have them for the 4G63 and consequently dont use them. This would cause the cynlinder walls to distort when the pressure of the head is applied and result in low compression numbers.

Michael

 

[autronicDSM]

Well i had some of the same problems in this area myself but over a little bit of break in time and also i hope your not running an synthetic oil right now cuz that will prevent the rings from setting corectly but ill have to agree check your lifters. Did you put the head back on ( i mean like put the lifters,followers,cams back in your self or did you have the other guy do it?) the reason i ask is if you dont compress the lifters before reinstalling them your going to have these problems.

Sorry if this didnt help but its just some things you might want to check on...

Why is synthetic oil bad for the break-in? Who told you that?

 

[boostedinaz]

Why is synthetic oil bad for the break-in? Who told you that?

Every engine builder/machina shop has always told me the same thing. Wait for at least a 1000 miles before you go to full sythetic. My guess is that it doesnt stick to the internals as well as the old school oil, but that is far from a scientific explantion.

Michael

 

[pneumo]

From what I've heard, synthetic oil is so good that it prevents the rings from making contact with the freshly honed cylinder walls. The rings need to press against the rough wall surface in order to bed in properly.

The break in procedure is also very important for getting the rings to seal well. If the break in procedure was messed up, the rings won't seal well.

So how was the engine broken in?

 

[GSX_Dan]

I broke it in according to Motoman's break in procedure. I used non-synthetic 100% motor oil, no additives.

http://www.mototuneusa.com/break_in_secrets.htm

I followed this guy's break in method almost to the letter. I had some problems during the first drive, the car started to miss but then resumed normal operation after about 5 minutes.

Basically I let it warm up fully, and went for a drive around the county. First 3 runs were at about 35% throttle in 3rd gear from 3000 to 5500 rpm, then the next 3 were at 60% from 3000-6000, and the last few were at 90-100% all the way up to 7000rpm. After each run I would let the engine slow down the car for the required vacuum to be created.

Does anyone know the clearance specs for the wiseco rings/pistons?

 

[pneumo]

What a coincidence. I rebuilt my motor with Wiseco 9.0 pistons last month. I still have the spec sheet, which lists the piston/ wall clearance at 0.0030"

The top ring should be set at 0.014" with the 2nd ring gap slightly larger. I couldn't find any hard numbers on what the 2nd ring gap should be, but 0.016" sounds good. I used 0.019".

I also did the Motoman breakin method, although I had good results.

 

[pneumo]

I just remembered something; Wiseco pistons use circlips to hold the wristpin in place. You said the engine ran bad for about 5 minutes, then cleared up? I'm wondering if maybe one of the clips popped out, got jammed between the piston and cylinder, chewed up the cylinder wall, then got spit out into the oil pan. The reason I'm saying this is because the open end of the circlip needs to be positioned a certain way or else it will pop out. I suggest calling some shops and ask them if they have anything like a fiber optic scope that will let you look into the cylinder and examine the walls. Hopefully you can find some clue without having to pull the head off.

 

[GSX_Dan]

Well the head was already off due to a blown HG. I have found most of the ARP head studs came loose, and they were around 60ft/lbs, nowhere close to the 71 I I set them at. They must've stretched with the heat cycling, so this time I torqued them down to 85ft/lbs and re-checked them after the warmup. I didn't have a chance to measure the cylinder wall clearance since I didn't have the tool. The compression now reads 155-171-176-165 after 800kms. As you can see it must've been the HG all along that was causing #2 to show low, but that still doesn't explain the 20-35psi I'm loosing still. I'll try doing another leakdown test to find out.

 

[1fast97gsx]

with the studs stretching or loosening you would still have oil on your coolant then though right? My compression is kinda messed up too 180-160-175-165 ... maybe I overtorqued the studs and stretched them? I figured I'd still have the oil and coolant mix if that was my problem but the studs seem to have fixed yours so I'm not sure now.

 

[GSX_Dan]

I had no oil/coolant mixing prior to the HG popping. It was running fine, not burning any oil or coolant until I went to the track and turned up the boost a little. That should teach me a lesson.