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How does someone bore an oval hole? Sounds impossible.
Run-out on the machine doing the bore could cause it. Unlikely in a shop that does these things all day as it would cause lots of issues for lots of jobs, but decidedly not impossible.
After boring comes honing. When honing it would be very obvious that the bore was out of round. Slightly tapered or out of round could or would be cleaned up by the hone.
Originally Posted by MetalMuffins
Run-out on the machine doing the bore could cause it. Unlikely in a shop that does these things all day as it would cause lots of issues for lots of jobs, but decidedly not impossible.
I would take it back to the machinist and have him assemble the bottom end. Something is causing the issue. If it blows a ring when your machinist does it then you can just burn the engine and throw it off a cliff and start over
I would take it back to the machinist and have him assemble the bottom end. Something is causing the issue. If it blows a ring when your machinist does it then you can just burn the engine and throw it off a cliff and start over
Funny, my last guy told me he would put it together. I just like doing things myself. That and I know he is always super busy. I went to him after my first failure, so I assumed any machining problems would be justified if I had them. I’ll let him put the bottom end together this time around, just hate moving along without finding answers. Does not give me much confidence to do it again. That and I really want to know where was my failure. I’m sure this will not be my last build.
Funny, my last guy told me he would put it together. I just like doing things myself. That and I know he is always super busy. I went to him after my first failure, so I assumed any machining problems would be justified if I had them. I’ll let him put the bottom end together this time around, just hate moving along without finding answers. Does not give me much confidence to do it again. That and I really want to know where was my failure. I’m sure this will not be my last build.
For sure brother I totally understand. It sounds like you had all your ducks in a row and it doesn't make sense that it failed. I've built two BP engines and both times I had my machinist assemble the bottom end, and I do everything else. I've done a bottom end on a 3sgte before with my buddies and it was fine when we did it. I just always feel good when my machinist assembles the bottom end because he's just really good.
Yeah, but still I really don’t feel like putting the bottom end together is hard, this part I enjoyed the most. All my measurements were confirmed both times, so I’m just really bummed. I could say that my first motor I didn’t confirm everything as well as this last motor, but dang, just may have got bitten with bad luck or something. Just keep feeling I’m missing some thing, or maybe life is what it is. Third times a charm. Lol.
One of my business partners owns a automotive machine shop. I do all of my own machining and assembly. If there is an issue I only have myself to blame. A side benefit is that if there is an issue I almost always find out what the real cause was. My current engine is using ST/Mahle pistons. The piston to wall is .0035-.004" and the ring end gap is .016-.017 & .019-.020. Good luck
What you describe sounds like ring seizure and not actually failure of the ring. I've had this a few times pushing two stroke dirt bikes and built boat motors very hard. Several things can cause this. One is as leona describes being insufficient piston to wall clearance for application. Second possibility is running too hot. The hotter you run the engine the more p2w clearance you need before ring seizure occurs. Third possibility is either very heavy knock or even pre-detonation. If you have pre-detonation you may not register any knock with typical knock sensors. Fourth is an oiling issue of some sort. What likely is happening in your case due to probably one or more of the previous mentioned issue is your piston is expanding to the point of basically an interference fit in the bore. The oil film cannot be maintained and piston/bore contact is happening. The heat is often enough to produce small pockets of molten aluminum which gets into ring groove, locking the rings. If engine is apart and you look very carefully at the bores you may even find a few areas where some small films of aluminum were even bonded to some parts of the cylinder walls. I,ve had a couple two stroke motors seize to the point of the motor locking up. After cooling, the engine freed up but the rings were stuck as you describe and no run. Hate to admit it, but in more than one occasion in my early years of playing and beating the snot out of two strokes I just took motor apart, cleaned the aluminum off the bores, redneck honed, freed rings and lightly sanded the pistons. Slapped that junk back together and ran with whatever sloppy clearance engine wound up with until I could do a more proper rebuild.
Yeah, but still I really don’t feel like putting the bottom end together is hard, this part I enjoyed the most. All my measurements were confirmed both times, so I’m just really bummed. I could say that my first motor I didn’t confirm everything as well as this last motor, but dang, just may have got bitten with bad luck or something. Just keep feeling I’m missing some thing, or maybe life is what it is. Third times a charm. Lol.
When was the last time you had your measuring devices calibrated/measured? Holding a tenth of a thou repeatability on a run of the mill mic isn't necessarily going to just happen if they aren't regularly calibrated.
The biggest problem with automotive machine shops is they don't know how to measure well. Almost everything in an engine can be a relative measurement and only the result of the two measurement's is needed. What that means is that calibration is not really needed. Good quality tools are a big help. For my most accurate and final check I use the micrometer that I measured my rod, main journal or piston to set my bore gage.
The biggest problem with automotive machine shops is they don't know how to measure well. Almost everything in an engine can be a relative measurement and only the result of the two measurement's is needed. What that means is that calibration is not really needed. Good quality tools are a big help. For my most accurate and final check I use the micrometer that I measured my rod, main journal or piston to set my bore gage.
Bingo! if you use the same tool for both measurements the cheap tools will work just fine!
This is the ONLY way to work in "tenths".
Even with the good tools...
Bingo! if you use the same tool for both measurements the cheap tools will work just fine!
This is the ONLY way to work in "tenths".
Even with the good tools...
I'm not so sure, but I also don't have first hand experiences measuring bearing clearences with crappy tools.
That said, I think you might be mixing up repeatability (precision) and accuracy. Agreed that you don't need to have, for example, your micrometer scale NIST calibrated every month, but there is still a big gap in precision between a Browne & Sharpe or Mitutoyo and a noname Amazon product. When I'm using a mic that's not mine I will always always check it against a high grade gauge block to make sure it hasn't been dropped or damaged. When 0.0001" (or lower!) matter, something as simple as the quality of the clutch or the weight of the oil lubricating the threads can result in a loss of repeatability easily on the order of a tenth of a thou.
Manufacturing components in volume is different then engine building. There is a need for calibration when an actual measurement is required and there are applications where just the difference between two is needed or a relative. In reality if your measuring in the sub .0002” then it is best to use non-contact tooling or fixed pressure tooling.
If you're taking a measurement to compare it to a pre-determined value you need the higher quality tool. Mitutoyo is an excellent choice. You're after the actual number. This is accuracy. This is OCD
If your taking two measurements to come to a "difference" the cheaper quality tool will work nearly as well and save $$
Even if the threading is off .001 over the span of the mic (which would be bad) the amount of threading you are using to make piston clearance determination is tiny; thus the un-accuracy of the cheap micrometer is tiny between two points on the same tool.
This is precision. A cheap tool can, if used properly, almost equal the most expensive...
I consider Mitutoyo as a "value" brand.
Most of my stuff is Starrett.
I'm badly OCD...
Try it next time you build something, measure with your good stuff and then borrow (or buy) some cheap stuff and use as described.
I was shocked
Very few can work in tenths, it's all about the feel.
From wiki In measurement of a set, accuracy is closeness of the measurements to a specific value, while precision is the closeness of the measurements to each other.
Back to the topic, I've received an engine from a machine shop with oval shaped cylinder bores, honed beautifully.
Don't discount retarded timing or a lean mixture creating abnormally high combustion chamber temperatures. It's too late to check base timing since things are disassembled. Check the balancer marks, too.
Back to the topic, I've received an engine from a machine shop with oval shaped cylinder bores, honed beautifully.
You're right Six, sorry
But ,andyfloyd brought up the oval bores, not the original poster.
whiprsnaper just said ring failure, twice, and 2nd ring more involved (which is weird, top ring takes more damage from too much heat)
Personally I think Newza made the best suggestions.
I'd like to see pictures of said pistons and rings.
One question that no one has asked is have you deleted the piston squirters and if you did not were they all checked for proper flow?
If they have been deleted how are you oiling the cylinder walls and piston pin?
A lack of oiling might be the culprit.
Another is what was the side clearance of the rings in the lands? Was it checked? This is often overlooked.
Was land depth verified? IE can the rings seat below the outer diameter of the pistons- this is a stretch, I've never run into this before but...
I agree on verifying accuracy of timing marks on balancer and carefully checking base timing when it's running again.
I'll go back to lurking
Actually this could have been a measurement issue and a little education about the process can help when having machine work done. This was obviously a piston seizure issue from inadequate clearance and maybe combined with poor tuning.
Retarded timing will raise the egt's which would cook the exhaust manifold, turbo and exhaust valve. Actually too much timing will raise cylinder and piston temps. Ovality would be rare and not the cause of this issue. It would cause excessive blow by and low cylinder pressure especially at idle. Although an extremely rich mixture could wash the cylinders and cause a lubrication issue.
The real issue is that ST on their instructions list the min piston to wall clearance as .00276" which is not enough for a turbo application and a forged piston. The piston to wall clearance is at 0 at 200F. Based on the 4032 alloys CLTE of 10.8 and the block at 6.
Originally Posted by sixshooter
Way to get lost in the weeds, guys.
Back to the topic, I've received an engine from a machine shop with oval shaped cylinder bores, honed beautifully.
Don't discount retarded timing or a lean mixture creating abnormally high combustion chamber temperatures. It's too late to check base timing since things are disassembled. Check the balancer marks, too.
As stated, probably piston to wall clearance being too small, or something in your tune is wicked fucked, since the second engine lived for 500mi before you added boost, and the first one basically died instantly under boost.
It was not piston to wall. I returned the block to my first machinist because he was tight. The first motor did not see boost, second motor started to fail upon introduction of boost after 500 miles. More toward 8-10 psi on a 2560. Timing was confirmed, I mark tbc from the piston, then confirm mark.
09-18-2020, 11:33 AM
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