Low compression after rebuild

[1glaserfwd]

Hey guys just need an opinion. I have a 99gsx that I did a 6 bolt swap which also is a 2.3. Bottom end is brand new manley pistons with 1g rods. Head is a 2g head with hks272 cams and dual valve springs. Running an hx40 t3 housing. I broke the engine in via the motoman method. After first 20 miles I changed the oil. Soon after I noticed that the engine smokes under decel only! After there is any load put on the engine it will smoke on deceleration. I then tried putting my stock vc back on with the factory pcv system in place thinking that could be the issue. Didn't really help much so at 60 miles I did a compression check and it was 115 across. Figured I would keep putting miles on it hoping for the smoke and compression to go up. I have been driving it fairly hard on 8psi then decelerating hard. I am at 200 miles now and changed the oil again. Smoking hasn't really let up and I did another test and its only 120 across. Remembering now on first start up the injectors weren't setup quit right and for the first 2 minutes was idling very rich. I am afraid that may have done me in getting a perfect break in. Should I keep driving it till 500 and retest or just pull the bi*** down and re ring it again. I am super bummed this is happening but I wanna get it addressed before our local track opens. I spent all last summer doing the full build and really wanna race this year. Really appreciate everybodys opinion and help.

 

[donniekak]

Do a leak down test, and see where you are leaking.

Also, stock rods aren't going to handle as much power in that stroker as they would with an 88mm stroke. I'd be Leary of cranking the boost up on that hx40 with that setup.

 

[thirsty]

G'day.
Smoke like this??

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The video works, press start.
I pulled my big 16 g down and discovered a slight oil leak from behind the heat shield on the exhaust side. Will be rebuilding when the kit arrives.
My compression 1-175; 2-185; 3-185;4-185.
Cheers
Ross

 

[tmoney20g]

Russ,
You're not the same Russel Cox that used to live in Virginia here in the US are ya ?

 

[thirsty]

No, sorry. Australian born and bred. Cheers

 

[inthemidst]

Did you use a metal head gasket without decking the block.

 

[motomattx]

Motoman method? another one bites the dust. When are people going to learn not to abuse a fresh engine like that? I have seen so many engine failures from the "motoman" method. This motoman guy has no experience as a mechanic and his methods were what he recommended on a DIRTBIKE engine at that. I am awaiting of course the 20 posts from people that will want to argue with me that they have used the beat on it method and their engine has lasted x amount of miles and x amount of dyno pulls/runs etc etc. Not looking to turn this into a break in debate so lets avoid all of that, but just saying there are alot of early failures on these forums when the person posting has used the "motoman" method.

 

[1glaserfwd]

The head was brand new 300 miles ago on a different setup so I don't think its the head causing low numbers. I am running a composite oem headgasket. I am just going to keep driving it and hope it the numbers come up.

 

[1glaserfwd]

Motomatt how do you break in your engines? Seems like the motorman method is pretty popular in the "race car" scene.

 

[lasthope05]

Tens of thousands of motors are broken in on the dyno or aggressively with perfect ring sealing. Drive the car hard on nondetergent oil with plenty of engine breaking has worked well on all my motors and ones ive built for others.

Who did the machine work? I also hope they're not stock bore pistons with diy hone with stones from the auto parts store.

 

[miliman13]

If you did not bleed the lifters, pump them and allow then to set in place it is with in the realm of possibility that that valves hung open enough to allow to piston to valve contact. Of course this is just one possible hypothesis. Now if you raised the rpms high when braking in and none of the above was done then it further strengthens my argument .- ask me how I know. Keep it intact and do weekly comp test on it, if there is no change then you will have to tear down.

 

[1glaserfwd]

The long block was assembled 3 months before the engine was started so definitely no problem with lifters.

Quick update i went and put another 75 miles on the car and i must say feels strong for only 8psi. Did another compression test and still 120. Decided to do a leak down and it was only 10% on all 4cylinders. Small hissing coming from the vc and dipstick. After reading 10% leak down isn't too bad. Maybe the cams are altering my readings by quit a bit.

 

[Type1DSMr]

Did you try to add a little oil during compression test?

 

[keltalon]

Motoman method? another one bites the dust. When are people going to learn not to abuse a fresh engine like that? I have seen so many engine failures from the "motoman" method. This motoman guy has no experience as a mechanic and his methods were what he recommended on a DIRTBIKE engine at that. I am awaiting of course the 20 posts from people that will want to argue with me that they have used the beat on it method and their engine has lasted x amount of miles and x amount of dyno pulls/runs etc etc. Not looking to turn this into a break in debate so lets avoid all of that, but just saying there are alot of early failures on these forums when the person posting has used the "motoman" method.

I don't think anyone is going to argue with you on this matter especially in a thread were the method didn't work. I guess we have to have some empathy and not beat the op up but try and find a way to help him with the issue, I know he feels bad about the engine not being up to par. .

 

[lasthope05]

The long block was assembled 3 months before the engine was started so definitely no problem with lifters.

Quick update i went and put another 75 miles on the car and i must say feels strong for only 8psi. Did another compression test and still 120. Decided to do a leak down and it was only 10% on all 4cylinders. Small hissing coming from the vc and dipstick. After reading 10% leak down isn't too bad. Maybe the cams are altering my readings by quit a bit.

Who built the motor or did the machine work though? Stock bore or overbore? That information can also help narrow down the issue.

Those numbers arent that great even with hks 272s. As overlap is so mild on them, compression numbers wouldnt be affected that much.

 

[keltalon]

Who built the motor or did the machine work though? Stock bore or overbore? That information can also help narrow down the issue.

Those numbers arent that great even with hks 272s. As overlap is so mild on them, compression numbers would be affected that much.

Good question!

 

[inthemidst]

I have to second the not bleeding the lifters and it knocked the valves just enough to cause a small compression leak.

 

[1glaserfwd]

The machine work was done by a local guy who builds a lot of evo and dsm engines. It's.20 over on the bore. Definitely not a problem with lifters, engine was fully assembled on an engine stand months before i started it.

 

[miliman13]

unless you know that valves are not bent, then you truly don't know what it actually is, so instead of taking a stance on one side of the field, how about you prove us all wrong/right or neither! pull your rockers off , thus sealing all your valves, then do a leak down. if you get solid seal then i am wrong, and then it must be your rings, and i know you don't want to prove me wrong because if so then your looking at a whole lot more work. Get back to us with results not beliefs, i say this respectfully as i wish you the best, but don't knock down the hypothesis until you can actually disprove it.- "drops mic"

 

[lasthope05]

I highly doubt the motor bent valves from a pumped up lifter. Lifters bleed down a few hours after install. With the motor sitting for a few months before starting, they would of already been bled. Now its not to say, he couldnt of bent valves from jumping timing but, he says the motor runs and feels strong. However, its still always good practice to check mechanical timing. Leaking valves can also be from rust /pitting of the seats if the head wasnt sealed/wrapped or a humid room.

Also, no need to remove rocker arms for a leakdown test. Just rotate the motor to TDC for each corresponding cylinder.

Personally, I would just run the motor more and see what happens. Even though compression numbers are low I've personally made over 500whp on tired stock motors. Enjoy the car now and in the off season tear her down and have the head checked over or re-ring the block then. Having low compression numbers isnt going to hurt the car, only performance slightly. Just make sure you have an adequate pcv system for extra blowby, but if it really bugs you then by all means do it now.

 

[1glaserfwd]

I highly doubt the motor bent valves from a pumped up lifter. Lifters bleed down a few hours after install. With the motor sitting for a few months before starting, they would of already been bled. Now its not to say, he couldnt of bent valves from jumping timing but, he says the motor runs and feels strong. However, its still always good practice to check mechanical timing. Leaking valves can also be from rust /pitting of the seats if the head wasnt sealed/wrapped or a humid room.

Also, no need to remove rocker arms for a leakdown test. Just rotate the motor to TDC for each corresponding cylinder.

Personally, I would just run the motor more and see what happens. Even though compression numbers are low I've personally made over 500whp on tired stock motors. Enjoy the car now and in the off season tear her down and have the head checked over or re-ring the block then. Having low compression numbers isnt going to hurt the car, only performance sihtly. Just make sure you have an adequate pcv system for extra blowby, but if it really bugs you then by all means do it now.

That's a lot man that's exactly what im going to do is just run it. If it doesn't come up then next winter I'll pull it down then.

 

[BogusSVO]

One thing that has been over looked.... HOW Accurate was the compression gauged used?

 

[arrowhead]

An engine should not be sitting for that longer period of time without at least rotating the motor by hand, rings could take a set and valve seats could also corrode some.
Before we had chassis dynos and were race motors and no access to engine dynos, these cars could not be driven on the streets so break in was very similar to motoman way.
Practically they were broken in at the track in practice and not really balls out during first race or so.

 

[1glaserfwd]

I used two different testers and got the same results. Matco and snap on. Also while the engine was on the stand i rotated it by hand every week or so.

 

[pmanaresi]

Hey I am experiencing a very similar scenario with my freshly rebuilt stroker 6 bolt. Engine runs like an animal but was experiencing some knock at high rpm. Just hit 500 miles and checked compression and found 115-120 psi. I did leave a larger ring end gap (.018 top ring and .023 bottom) and have a .005 ptw clearance. Not sure what is normal to expect for a "loose" engine like mine is set up, but I figured it would be closer to 170psi at least. I used Manley rods and wiseco 8.8/1 Pistons. I also used the "motoman" method and changed the oil after the first 20 mile test run. Anyone running similar clearances and have compression numbers to compare? And if this is lower than to be expected should I ball hone and rering with same end gaps or just drop in the rings pregapped to achieve a smaller gap?