Piston rings not seating

[715Hunter]

As an aside, we had a piston break in our work truck last month. It scored the wall slightly, but mostly left residue. We ordered a new piston and a dial bore gauge, and cleaned the cylinder up with a wiper hone and a drill. This hole was slightly smaller than the other ones, so were able to open it about .001" and get all the scoring out except one tiny spot about .25" long. Did a compression test after it was back together, and that one is higher than all the other.
I find it ironic that we're beating a $100k hone machine with a wiper hone and drill.

 

[2004LB7]

post back in 100k miles and let us know what the compression is

As an aside, we had a piston break in our work truck last month. It scored the wall slightly, but mostly left residue. We ordered a new piston and a dial bore gauge, and cleaned the cylinder up with a wiper hone and a drill. This hole was slightly smaller than the other ones, so were able to open it about .001" and get all the scoring out except one tiny spot about .25" long. Did a compression test after it was back together, and that one is higher than all the other.
I find it ironic that we're beating a $100k hone machine with a wiper hone and drill.

 

[Bdsankey]

Kinda. He says there rings were too hard for awhile when pistons were so hard to find, which is when I bought mine. But he thinks different oil will help over time.

But I agree with this. With what I've learned recently, oil is kinda unimportant, at least for initial performance.

I plan to take my truck to their shop sometime next week and let them see it, and ask what they'd like to do.
Right now I'm thinking I'll tear it down and take pictures all the way, measuring everything, etc.
Just an FYI, these is the exact piston and ring set I bought. https://www.xtremediesel.com/mahle-motorsports-cast-duramax-performance-pistons?variant_id=112366
If it doesn't show up, .020" over, 4.075".

This ring pack is a pretty decent ring pack. I've used that exact piston kit many times and have NEVER had the issue you are which leads me to believe it's poor machine work and he's trying to get you out of the warranty period................

 

[715Hunter]

That's pretty shitty but not mind-blowing. Hopefully I'll get a chance to tear it down in the next month.

 

[Bdsankey]

That's pretty shitty but not mind-blowing. Hopefully I'll get a chance to tear it down in the next month.

Why not bring it back and demand it be fixed OR if they want you to try a different oil you should demand that in "X" amount of miles if it doesn't improve it will be repaired regardless of warranty status.

 

[715Hunter]

Why not bring it back and demand it be fixed OR if they want you to try a different oil you should demand that in "X" amount of miles if it doesn't improve it will be repaired regardless of warranty status.

Because they sent it out as a short block, they do not have a specific "warranty". They will stand behind something that is their problem, but I am kinda on my own.

 

[West]

Since you installed the heads did you check deck height? If the pistons were down in the hole you lose a lot of compression. Would not cause blow by but might cause low compression. Most builders say you need .040 deck clearance between the piston and cylinder head but your head gasket gives you most of that .040 so knowing the deck height of the pistons helps build a good engine.

 

[Bdsankey]

Because they sent it out as a short block, they do not have a specific "warranty". They will stand behind something that is their problem, but I am kinda on my own.

A short block with rings not sealing sure sounds like their problem unless I'm missing a key component to this story....

 

[715Hunter]

Since you installed the heads did you check deck height? If the pistons were down in the hole you lose a lot of compression. Would not cause blow by but might cause low compression. Most builders say you need .040 deck clearance between the piston and cylinder head but your head gasket gives you most of that .040 so knowing the deck height of the pistons helps build a good engine.

I didn't check protrusion, but I asked them what gasket grade to go with and rolled with that.

A short block with rings not sealing sure sounds like their problem unless I'm missing a key component to this story....

Agreed. But seeing as I haven't gotten very far with him on the phone, I want to take the truck there and let him see for himself what's going on.
And even then, my work is so crazy I don't know when I'll have time to pull the engine and strip it down.

 

[Chevy1925]

Since you installed the heads did you check deck height? If the pistons were down in the hole you lose a lot of compression. Would not cause blow by but might cause low compression. Most builders say you need .040 deck clearance between the piston and cylinder head but your head gasket gives you most of that .040 so knowing the deck height of the pistons helps build a good engine.

He would need the piston to be 1/4" below deck height for a compression number he is posting. 250psi compression is typical of bent rods with that amount of clearance below deck height.

p to h clearance is usually .025-.028ish range for a stock power build. pistons will protrude .012 out of the block.

its not his issue unless hes bent his rods.

 

[West]

Chevy, you are correct .040 is too much Piston to Head clearance in a Duramax. I quoted a known number for automotive engines which have more RPM and with more RPM you have more rod stretch and need the extra clearance. The Duramax only spins maybe 5,000 RPM Max so a tighter quench or piston to head is fine.
The factory offered head gaskets in .035, .037 and .039 thickness to give better compression with each set up. Tolerances vary when building engines and this allowed the factory some wiggle room to keep each engine similar for compression.

I have read that .003 difference in Piston to head clearance can make a 1/4 point difference in compression ratio on a Duramax because of the flat Cylinder head with no chamber to speak of. Even the small valve reliefs in pistons for big cam engines lowers the compression a fair amount.
Do his pistons have valve reliefs added so he could add more cam and were they 16:1 or 16.5:1 pistons. He listed his parts I guess I should have gone back and looked to see.
I still think he should know what his deck height is before moving forward. If he is .007 to .013 he is good and can choose a gasket to match.

I am guessing his block was decked as part of the rebuild and his heads may have been surfaced, figure .004 each and he gained .008 effective deck height change which would raise his compression but as we know, something is wrong because his compression is low.
Low compression is bad for power making but by itself does not create any blow by so he still has another problem which is most likely cylinder finish or maybe Std rings on his .020 over pistons. Something is wrong.

 

[danzick]

I'll be interested to see what you find. I just assembled an engine myself, and have about 500 miles on it now. Same pistons, and bore size. While I have had other set backs, blow by isnt one of them. I didnt even run it hard until about 200 miles. I was afraid to haha. I didnt have to file the second ring as all 8 ended up at .023 or .024 , but I did file the top ring. If i recall, it was .012 and I wanted .015- .016. All of my bores were within .0005 of the 4.075. i'm curious, is there any other issues with the blow by other than it leaking oil all over? like poor running or idling? how much oil are you having to add?

 

[Bdsankey]

Chevy, you are correct .040 is too much Piston to Head clearance in a Duramax. I quoted a known number for automotive engines which have more RPM and with more RPM you have more rod stretch and need the extra clearance. The Duramax only spins maybe 5,000 RPM Max so a tighter quench or piston to head is fine.
The factory offered head gaskets in .035, .037 and .039 thickness to give better compression with each set up. Tolerances vary when building engines and this allowed the factory some wiggle room to keep each engine similar for compression.

I have read that .003 difference in Piston to head clearance can make a 1/4 point difference in compression ratio on a Duramax because of the flat Cylinder head with no chamber to speak of. Even the small valve reliefs in pistons for big cam engines lowers the compression a fair amount.
Do his pistons have valve reliefs added so he could add more cam and were they 16:1 or 16.5:1 pistons. He listed his parts I guess I should have gone back and looked to see.
I still think he should know what his deck height is before moving forward. If he is .007 to .013 he is good and can choose a gasket to match.

I am guessing his block was decked as part of the rebuild and his heads may have been surfaced, figure .004 each and he gained .008 effective deck height change which would raise his compression but as we know, something is wrong because his compression is low.
Low compression is bad for power making but by itself does not create any blow by so he still has another problem which is most likely cylinder finish or maybe Std rings on his .020 over pistons. Something is wrong.

The bolded/underlined info is not correct. Surfacing the head on a flat head (like diesels) does nothing to change compression. If I take 0.004" off a flat surface I still have a flat surface, I did not change a combustion chamber volume etc as there simply is no combustion chamber to remove/change. Valve recession should have been checked/adjusted as needed by the machine shop at the time they did any head work.

 

[Chevy1925]

Chevy, you are correct .040 is too much Piston to Head clearance in a Duramax. I quoted a known number for automotive engines which have more RPM and with more RPM you have more rod stretch and need the extra clearance. The Duramax only spins maybe 5,000 RPM Max so a tighter quench or piston to head is fine.
The factory offered head gaskets in .035, .037 and .039 thickness to give better compression with each set up. Tolerances vary when building engines and this allowed the factory some wiggle room to keep each engine similar for compression.

I have read that .003 difference in Piston to head clearance can make a 1/4 point difference in compression ratio on a Duramax because of the flat Cylinder head with no chamber to speak of. Even the small valve reliefs in pistons for big cam engines lowers the compression a fair amount.
Do his pistons have valve reliefs added so he could add more cam and were they 16:1 or 16.5:1 pistons. He listed his parts I guess I should have gone back and looked to see.
I still think he should know what his deck height is before moving forward. If he is .007 to .013 he is good and can choose a gasket to match.

I am guessing his block was decked as part of the rebuild and his heads may have been surfaced, figure .004 each and he gained .008 effective deck height change which would raise his compression but as we know, something is wrong because his compression is low.
Low compression is bad for power making but by itself does not create any blow by so he still has another problem which is most likely cylinder finish or maybe Std rings on his .020 over pistons. Something is wrong.

stick with giving info about these engines, not gassers. if you dont know, its ok to sit and just read without commenting

you are missing the point in my post. the compression psi is plenty of info for his issue. if you take into account what im stating and realize the drastic difference he will need to see for a compression ratio, you will see why the .25 point of a ratio is not his issue and far from it. You have not done hands on experience with these engines and are just throwing numbers around that are really more confusing the situation for those that dont understand than it is helping at this point.

as brad stated, cut the head all you want, besides recessing the valves correctly, you are not going to get a compression ratio worth noting or causing a change as the only variant you adjusted is the small valve volume which is then a mute point if the valves are recessed back to factory. BUT i digress as it doesnt matter in his case, its not a compression ratio issue.

 

[Bdsankey]

stick with giving info about these engines, not gassers. if you dont know, its ok to sit and just read without commenting

you are missing the point in my post. the compression psi is plenty of info for his issue. if you take into account what im stating and realize the drastic difference he will need to see for a compression ratio, you will see why the .25 point of a ratio is not his issue and far from it. You have not done hands on experience with these engines and are just throwing numbers around that are really more confusing the situation for those that dont understand than it is helping at this point.

as brad stated, cut the head all you want, besides recessing the valves correctly, you are not going to get a compression ratio worth noting or causing a change as the only variant you adjusted is the small valve volume which is then a mute point if the valves are recessed back to factory. BUT i digress as it doesnt matter in his case, its not a compression ratio issue.

For compression to be that low something is majorly wrong. Like you (and others) have stated over and over, this isn't an issue that is going to require some teardown to determine where the issue lies.


To the OP, I wouldn't take anything apart in the bottom end (IE don't go beyond a short block) until you talk to the builder. It may not be a bad idea to record that call if you have any concerns that they will try and weasel their way out of something.

 

[08lmm72mm]

Given how the OP said this shop has had similar issues in the past with other customers builds I'd say it safe to say where the f'up is

 

[West]

Wow, tough group. I think it is established his rings are not sealing. Compression is low, blowby is excessive.
On tear down I would want a neutral seat of eyes to see what his piston to wall clearance is. What are the ring gaps. What does the cylinder finish look like. Verify cross hatch is at the 45* angle as stated. Sharper angles make the rings spin fast in the bore. Flatter angles slow the ring spin down. Rings always spin while operating, the spin is created by the cross hatch. It helps the rings seal.

 

[Bdsankey]

Wow, tough group. I think it is established his rings are not sealing. Compression is low, blowby is excessive.
On tear down I would want a neutral seat of eyes to see what his piston to wall clearance is. What are the ring gaps. What does the cylinder finish look like. Verify cross hatch is at the 45* angle as stated. Sharper angles make the rings spin fast in the bore. Flatter angles slow the ring spin down. Rings always spin while operating, the spin is created by the cross hatch. It helps the rings seal.

Not so much a tough group but if you post information that is wrong it will end up being corrected by at least one persons. Stating that decking the heads will change compression is a tell tale sign that you do not have a ton of experience on diesel platforms.

Nobody is discrediting the experience you may have, but you also then know that diesel vs gas is not always 100% apples to apples (and heads are certainly one major difference).

 

[West]

I had two Durmax heads surfaced two months ago, they did not need a valve job. They took .004 off one head and .006 off the other to clean up the surfaces and make sure they were straight. Since it did not need a valve job this work was done without removing the valves. The valves did not get touched by the cutters on the CBN surfacer. They are a little recessed from the factory. In my case they are less recessed now with the heads surfaced. That does affect compression. If you have a valve job done the machinist has control over how much the valves are recessed with the valve job or if new valve seats are installed. I spoke with my machinist and we had no issue surfacing the heads this way even though GM would say to recess the valves to match OEM. Surfacing the head can affect compression, not as much as decking the block though. And you are correct, I had 20 years in mostly Gasoline engines and maybe 5% Diesel work and then the last 12 years I worked was 95% Diesel but 80% was Cummins, Detroit and Cat very little small diesels like the Duramax or Powerstroke. I do not know the Duramax well specifically but I like the engine and the power and efficiency of it when tuned properly.
I am interested to see if this owner ever finds a solution because nothing is more painful than to spend hard earned money on the best parts you can choose and have a failure leading to weeks of hard labor and more expense.

 

[Bdsankey]

I had two Durmax heads surfaced two months ago, they did not need a valve job. They took .004 off one head and .006 off the other to clean up the surfaces and make sure they were straight. Since it did not need a valve job this work was done without removing the valves. The valves did not get touched by the cutters on the CBN surfacer. They are a little recessed from the factory. In my case they are less recessed now with the heads surfaced. That does affect compression. If you have a valve job done the machinist has control over how much the valves are recessed with the valve job or if new valve seats are installed. I spoke with my machinist and we had no issue surfacing the heads this way even though GM would say to recess the valves to match OEM. Surfacing the head can affect compression, not as much as decking the block though. And you are correct, I had 20 years in mostly Gasoline engines and maybe 5% Diesel work and then the last 12 years I worked was 95% Diesel but 80% was Cummins, Detroit and Cat very little small diesels like the Duramax or Powerstroke. I do not know the Duramax well specifically but I like the engine and the power and efficiency of it when tuned properly.
I am interested to see if this owner ever finds a solution because nothing is more painful than to spend hard earned money on the best parts you can choose and have a failure leading to weeks of hard labor and more expense.

You seem to still be stuck on this notion. Surfacing a duramax head has absolutely ZERO effect on compression. We can argue this point till the cows come home or until pigs fly, the facts remain the same. I don't know why you believe that taking material off an already flat surface (no combustion chamber/volume) is going to change compression.


Sure, if I don't touch valve recession I theoretically have slightly increased the static CR because now the volume between the valve face and the cylinder's deck surface is now decreased. Can you measure this change? Absolutely. Is it going to actually change enough to even be 0.1 point? Unlikely.