Why did this happen?

[GSX_Dan]

Ok, to make a long story short I had the block bored 20thou and I got the matching Wiseco pistons for this bore in the 9:1cr. I had the whole job done of boring, honing, and piston/ring mounting and then piston/rods installed in the block done by a local machine shop and he checked all the clearances. (bore size=3.366, ring end gap=.014-.016, rod clearance=.0018, main clearance=.0021)

I haven't had 192 psi compression since day 1, more like 135-95-175-155psi. I went on to run a 12.2@112 like this, but that's beside the point. Well 5000km later I took it apart to find the reason of the problem and I found signs of piston damage above the compression rings right below the crown on #2 piston most likely from detonation, as well as slight wear in the skirts of ALL the pistons and you can see the slight marks well since they're coated. So 2 of the cylinders have visible damage on them probably due to detonation, however I can only feel the damage in 1 cylinder when I go over with my finger nail(#1 cylinder, the right one in the pic) so honing should probably take this out.

What I am more conerned about are the slight marks in the sides (skirts) and why this would happen as I don't think this happened due to detonation, they are slight up/down scratches that aren't visible in the bore at all and the coating is worn off in a definite pattern on all the pistons. Keep in mind that I had low compression even in the un-detonated cylinders right from day 1.

Now my question is what could be the problem and why did I never achieve 9:1 compression? Should I be questioning my machinists' work? Is this normal wear on the skirts? I plan on checking clearances and the bores in a few days and I'll post my results. Any info would be appreciated. Thanks.

 

[Mirage2LTurbo]

Shitty machine work + shitty tuning = (see above)

 

[diambo4life]

I haven't had 192 psi compression since day 1, more like 135-95-175-155psi. I went on to run a 12.2@112 like this, but that's beside the point. .

No it isn't!


Seriously, wtf didn't you take the motor apart and send your shortblock back to the machine shop immediately after you found out that it had bad compression? You paid for that work, did you not? No point in doing it now. They will not honor anything especially after you detonated the pistons at the track. I wouldn't either.
That just shows recklessness on your part. What puzzles me even more is the fact that you took it to the track in that condition. It's people like you who end up complaining and bitching how shitty DSMs are due to sloppy work.

What piston-wall clearance was used on the Wiseco's? You didn't even provide enough info. as to what was actually done.

 

[WikedSicc]

Did your machine shop properly hone the cylinder walls for the Wiseco pistons. This changes from piston to piston. I know that the Wiseco pistons require a 280 grit hone.

 

[kalla]

That looks like it was caused by improper machine work and assembly. Like the previous poster mentioned, you should have taken the motor back to them after the initial break in when the compression numbers did not dial up as expected. Why you ran it at the track anyway with those bad (especially the very bad one on #2) is beyond me.

Also, you obviously have the tools to disassemble the motor, so why didn't you just assemble it yourself after the machine shop did the work? At least then you can check the clearances yourself and you have only yourself to blame if the above happens.

 

[Defiant]

No it isn't!

Thank you for saving me from having to type that.

I've had one bad motor in all my years, and it was because the machine shop missed on the piston/bore cut. It was just a Datsun 610 wagon, so I didn't much care. That poor slug drank oil its whole life.

Your machine shop effed the pooch, and you burned the motor up by leaving it in there.

 

[92redman]

Did your machine shop properly hone the cylinder walls for the Wiseco pistons. This changes from piston to piston. I know that the Wiseco pistons require a 280 grit hone.

While I don't disagree this was a problem with machining, I don't think the finnish of the stone had anything to do with the pistons. The stone grit and cross hatch angle are important to the rings sealing properly. Improper cylinder finish would not contribute to the compression numbers he listed, I would be more concerned with the piston/cylinder clearance and ring gaps.

 

[kalla]

I would be more concerned with the piston/cylinder clearance and ring gaps.

And both of these can be easily double checked once you have the block home from the machine shop, assuming you are doing the assembly yourself.

 

[GSX_Dan]

No it isn't!


Seriously, wtf didn't you take the motor apart and send your shortblock back to the machine shop immediately after you found out that it had bad compression? You paid for that work, did you not? No point in doing it now. They will not honor anything especially after you detonated the pistons at the track. I wouldn't either.
That just shows recklessness on your part. What puzzles me even more is the fact that you took it to the track in that condition. It's people like you who end up complaining and bitching how shitty DSMs are due to sloppy work.

What piston-wall clearance was used on the Wiseco's? You didn't even provide enough info. as to what was actually done.

Ok, take a chill pill, bud. There is no need to be rude, I am simply asking a techinal question and I'm not looking for smart a$$ replies such as yours, I don't even see why you waste the time of day to write such insulting replies. I had certain reasons not take it back to the shop at the time due to a number or reasons including the fact that the car is my daily driver and a complete engine removal and teardown would've cost me more time and money and yes, the car ran just fine once the knock sensor was fixed, and I was able to personally tune it to run a 12.2@112 on an e16G@18psi on pump gas, free of knock. The car ran fine,it ran fast, and compression wasn't changing. I made a consicous decision knowing that it will not last forever and I was planning on taking it apart just when I did, during the winter. Also I do not appreciate being generalized especially when I haven't even hinted to the fact that I will bad mouth DSMs.

I am also not looking to get reimbursed for the damage after a full season of racing, of course not, who would? Again, words are being put in my mouth...However I would still like to know IF the shop made a mistake I will not deal with them again, that's why I'm in the process of acquiring the proper tools to measure the clearances.

Also this was my first experience with rebuilding a motor and had no practice or much knowledge of setting up clearances/engine assembly procedures at the time so I left all of the blueprinting and assembly of the shortblock up to the machine shop, inlcuding piston to wall clearance, ring end gap, honing finish, etc. I assumed he knew all this stuff since he came higly recommended from quite a few high HP V8 guys around here. Now that I'm learning all this stuff I will never let anyone else work on my stuff again unless it's work I can't complete without the proper tools that I can't get.

I will be checking ring end gap/piston to wall/and bore size tomorrow and I'll post the results.

Thanks to all who gave worty replies and not turn this technical thread into a bi*** fest.

 

[Turbo Talon DL]

I feel your pain I had a machine shop go through my block.. To my dismay, they used undersized rod bearings, and i had piston slap. My cyl walls looked almost as bad as yours. I only have 300 miles on my motor and no track time. I didnt even get a chance to race But yeah...next time i see a shop with big blocks and pushrods sitting around, im gonna turn around really quick. The only thing that puzzles me is how i had good compression with that much piston slap going on. I can tell just by me being able to move the piston back and forth with my fingers with little effort that there is at least 1/16" of extra clearance that wasnt there when i put it all together and fired it up. I still had crosshatches too.. :thumbdown

 

[Defiant]

the car ran just fine once the knock sensor was fixed, and I was able to personally tune it to run a 12.2@112 on an e16G@18psi on pump gas, free of knock.

Waitaminute. You not only had a dead cylinder, but you were also running without a knock sensor? And you're still asking what happened?

In all honesty, I really don't know what to tell you. I guess that overall, cars have become so usually care-free that you forgot how crucial some of the obvious details are.

Good luck.

 

[diambo4life]

Ok, take a chill pill, bud. There is no need to be rude, I am simply asking a techinal question and I'm not looking for smart a$$ replies such as yours, I don't even see why you waste the time of day to write such insulting replies. ....

....Thanks to all who gave worty replies and not turn this technical thread into a bi*** fest.

Rude? I am just telling you the truth. You may not like it, but it's still the truth. It was negligence on your part. Any smart person who had invested hard earned money into their motor would not have done what you did. The car did not run "just fine" with that crappy compression, sorry. It was just an illusion for excusing your ineptitude. Tear down the motor, take measurements, THEN we can give you "real help." Otherwise, your post is just like any other fishing for sympathetic replies. I will not give you any. If my generalization offended you, I'm sorry for that. Otherwise, measure those clearances first and we can start from there.

 

[gixrman]

Did'nt see anyone else mention it but did the machinist use a boring plate? Thats a expensive $$$ FUBAR. I would contact a DSM machine shop for your next motor. Good luck.

 

[GSX_Dan]

Waitaminute. You not only had a dead cylinder, but you were also running without a knock sensor? And you're still asking what happened?

In all honesty, I really don't know what to tell you. I guess that overall, cars have become so usually care-free that you forgot how crucial some of the obvious details are.

Good luck.

I was running with a dead knock sensor and I only found out later after I was hearing/feeling the detonation and I was getting no knock readings. That is also the reason why the motor pre-build up put a hole in the piston.

I am also not sure if the shop used a torque plate, I didn't know to ask that question at the time...I know, my mistake for not specifying exactly what I want done.

I also just found out from the receipt he gave me it was a "plateau finish" hone. Would this be appropriate for the Wisecos rings? What about the .014-.016 ring end gap?

 

[TargeT]

after I was hearing/feeling the detonation

well i think you can forget the machine shop..

how long after you got the block back did you do that compression test...?

 

[diambo4life]

I What about the .014-.016 ring end gap?

According to Brian Nutter of Wiseco Pistons, that is sufficient on their newer pistons for the #1 compression ring. However, the gap for the second one has to a little bigger than that. Now the question is, what was the 2nd ring end-gap?

"Plateau" finish is ideal as well.

 

[GSX_Dan]

Allright, I finally got around to measuring the endgaps, piston diameters and started on the bores for cylinders #3&4. So far so good for the bores, they're within spec and that would give the piston a .003 clearance that it needs. The piston diameters only vary by .0005 which is normal from what I read. Now comes the ring end gaps and those seem to be a bit out of spec I think, on the larger side of things for the 1st one and on the smaller side for the 2nd one. It should be the other way around shouldn't it? Kinda weird the 2nd one is tighter, according to Wiseco the 2nd is supposed to be larger to prevent pressure build up between the compression rings. Could this be the fatal compression loss problem right from the beginning?

TargeT: I did the compression test after I came back from first break in drive that took about 1 hour and 50-70km. (I'm in Canada )

Here is all the data I gathered, there are multiple sheets just look at the bottom:

http://www.geocities.com/cutie_poo_69/clearances.xls