Piston thrust face scuffing, Eagle rods?
Piston thrust face scuffing, Eagle rods?
(OP)
I recently rebuilt a Nissan SR20 turbo charged engine. Ran fine for around 2000 miles. Pulled it down due to another failure and found thrust face wear on the forged pistons.
We installed some Arias forged pistons and Eagle H-Beam rods. These rods however do not have a thrust face oil squirter hole, whereas the factory rods do.
Piston number 1 started to scuff lightly, 2 and 3 are perfect, and 4 is quite bad.
I am chasing the cause. Given some cylinders are ok and some aren't has me confused. I assume that as the rods do not have the thrust squirters on them, they rely on the splash from the crank to lubricate the thrust face. Would it therefore be fair to say that two and three's bearing clearances on the conrods might be greater, thus passing more oil to lubricate the bores more?
At no point had oil pressure seemed to be a problem as far as I know.
Any ideas on stopping this happening again?
Run more clearance on the con rod bearings to help pass more oil?
Or drill a tiny hole where the thrust oil squirter should be?
Any advice would be great.
Thanks in advance
Jeff Meager
We installed some Arias forged pistons and Eagle H-Beam rods. These rods however do not have a thrust face oil squirter hole, whereas the factory rods do.
Piston number 1 started to scuff lightly, 2 and 3 are perfect, and 4 is quite bad.
I am chasing the cause. Given some cylinders are ok and some aren't has me confused. I assume that as the rods do not have the thrust squirters on them, they rely on the splash from the crank to lubricate the thrust face. Would it therefore be fair to say that two and three's bearing clearances on the conrods might be greater, thus passing more oil to lubricate the bores more?
At no point had oil pressure seemed to be a problem as far as I know.
Any ideas on stopping this happening again?
Run more clearance on the con rod bearings to help pass more oil?
Or drill a tiny hole where the thrust oil squirter should be?
Any advice would be great.
Thanks in advance
Jeff Meager





RE: Piston thrust face scuffing, Eagle rods?
Did you set the rod bearing clearance on the tight side? How much side clearance--if too little that will reduce oil throw too.
RE: Piston thrust face scuffing, Eagle rods?
The bearings reinstalled after the rebuild were of the same specification as original. Nissan do a numbering coding system on their stuff and we just replaced same with same. Knowing however that we were using different rods with the same crank, I plastigauged the bearing clearances to be sure they were ok.
Nissan spec the clearance to be 0.0008-0.0018 in.
My measurements came to cyl 1,3,4 - 0.0015, cyl 2 0.001.
That would therefore indicate that bearing clearance to be no issue, as cyl 2 and 3 are not worn, but one of those has tight clearance.....
I did not (my big mistake maybe) measure the side clearance. Not knowing how I could change this anyway, I didn't check. I now will be checking this....
Any other ideas? Could that cylinder be running lean causing more expansion? I would have thought though that the expansion wouldn't matter until such point as siezing occurred between both sides?! And as only the thrust is worn.....
Thanks
Jeff
RE: Piston thrust face scuffing, Eagle rods?
RE: Piston thrust face scuffing, Eagle rods?
There are many of these outputting much more, so I don't think this is the problem.
The Eagle rods are specifically designed as a factory replacement, so I doubt they would be incorrect, but never assume, I know. I shall check this .....
The oil holes in the pistons are for returning oil from the bore from the oil rings, correct? They are not for PUTTING oil on the bore are they? I'm sure not....
Jeff
RE: Piston thrust face scuffing, Eagle rods?
RE: Piston thrust face scuffing, Eagle rods?
RE: Piston thrust face scuffing, Eagle rods?
RE: Piston thrust face scuffing, Eagle rods?
Also, how clean were the bores on assembly.
How uniform was the block temperature as you bedded in the rings.
Regards
pat
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RE: Piston thrust face scuffing, Eagle rods?
The side loads were actually higher on the non-thrust side.
OK, let the "how come" guesses start!
RE: Piston thrust face scuffing, Eagle rods?
Regards
pat
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Please see FAQ731-376 for tips on how to make the best use of Eng-Tips Fora.
RE: Piston thrust face scuffing, Eagle rods?
Although some people like ARIAS pistons we have had several problems associated with these & now use an alternative brand with no problems.
All the suggestions above are good & i'd say your definately tight on your rod clearances for your application.
Where are the scuff marks ie are they in the middle of the skirt or are they offset from the middle or are they both sides of middle etc.
Cooling to No 4 pot could be an issue also, maybe it would pay to test the coolant flow while the engine is torn down.
Do the bearings on No 4 rod journal show any signs of being hot etc indicating low oil pressure or in sufficient oil, also is the radius on the crank rod journal correct.
If you fit a bearing shell to the rod cap & place it on the journal you can check to see if the bearing shell has sufficient clearance to the radius, if not it may interupt the oil flow.
RE: Piston thrust face scuffing, Eagle rods?
Not factory forged, correct. The block was bored with a torque plate (alloy block with steel liners), and taken out to the necessary clearance as specified with the pistons.
I cleaned and cleaned the bore knowing of the possibility of problems with this and yes, they were as clean as I could get them. I'm sure I rag tested them and they came out clean.
Smokey, we tried to stick within the specs as per the nissan manual for the engine. These engines are known to run very tight clearances throughout the engine. This however may also give the reason for the conrod thrust squirters, as they run tight bearing clearances, more oil is needed.....
Cylinder 4 is very galled up. About the size of your thumb. Cyl 1 has only 1 or two vertical lines.
As for pre-oiling. I would shake and lower my head and say no. We used a tub of redline engine assembly lube and thoroughly coated everything with this stuff. But I must say, the more I think about it, the more it is quite possible that not putting oil/engine lube directly to the piston walls (instead of just the pistons) could have meant there was not enough lube on the walls prior to startup.
The engine wasn't pre-pressurised as I have read about since. We setup the engine, and cranked it to get up oil pressure (disconnecting efi so it wouldn't start). Once oil pressure was up, we went for it.
Is this a bad move, or ok?
Finally in summary. I think even though there was probably a lack of cyl wall lube due to not pre-oiling, the pistons were dripping i assembly lube, and cyl 2 and three are ok so I'm not convinced. (but it's hard to know)
Smokey, can you ellaborate on the machining you are talking about?
Thanks everyone
Jeff
RE: Piston thrust face scuffing, Eagle rods?
I am skeptical. The arias take away a fair bit of the pin offset that is there in the factory units. Ie, it was easy to measure the factory offset, nearly impossible to tell the the arias, but there is a tiny bit.
Scuffing is on the middle of the pistons.
OK, can someone point me to a site with pics of good versus bad bearings please. As far as I know, they are fine. There is no discoloring to any of the bearings. The only signs on the bearings are shiny patches where they are wearing. Mostly they still retain their dull, brand new look.
Finally, as part of the rebuild, I am putting in a higher flowing oil pump. Can I expect this to help the situation in the future? I am not saying that I will use this to "fix" the problem. I am very keen to know more about what could be wrong to fix it the right way, rather than to bandaid it up another way....
Jeff
RE: Piston thrust face scuffing, Eagle rods?
Regards
pat
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RE: Piston thrust face scuffing, Eagle rods?
I don't think lack of oil to the bearing is a problem, more likely the lack of oil squirted onto the thrust face by the rod.
How would pin offset affect thrust wear? ie, being the arias have less offset? It still doesn't explain why two cylinders are fine.....
RE: Piston thrust face scuffing, Eagle rods?
ok, as mentioned previously, Nissan bearing clearance specs are 0.0008 to 0.0018in.
I had about .001 to .0015.
If I was to go to .0025in clearance, what negative effects do I have other than loss of oil pressure do to excess oil being lost to spray?
Am I mad to go out of factory specs for this? Although it's not like I'm sticking to factory specs for power etc am I....
Will it cause failure by running larger clearance?
It would be fair to say that the main bearings would have no affect on the splash to the crank as they are not flying up and down?!
thanks
RE: Piston thrust face scuffing, Eagle rods?
Yup, the oil will go where the grease won't.
RE: Piston thrust face scuffing, Eagle rods?
RE: Piston thrust face scuffing, Eagle rods?
RE: Piston thrust face scuffing, Eagle rods?
No, not related to pin offset. Here's a big clue-it couldn't have happened on a single cyl. engine, and highly unlikely on a twin, 4, 6 or even an 8.
Back to the problem. Pre-oiling-I don't think the lack of it caused anything. 2 strokes are commonly built w/o oiling the piston/rings/bores in order to quickly seat the rings. Do the mods posted here and you should be OK.
RE: Piston thrust face scuffing, Eagle rods?
I neglected to tell you why the engine was dead. Now I can't say which came first (its a chicken and egg situation - which came first), but the engine was stripped due to having a catastrophic death. We theorise that a rocker broke up top (Overhead cam engine, 1 lobe per two valves setup on a 1.43 rocker ratio for lift etc) causing the top end to jam, the bottom kept going, somehow the chain has jumped off the bottom cog, the top has freed up and pistons met valves. All 16 valves bent, 5 rocker smashed when they had no where to go when the piston pushed the valves up.
Now as the wear is older than just the death I didn't mention it as not to cloud the discussion, but after taking the back piston to the machinist, he noted two sets of valve marks. One set was carbon coated, the others were silver/fresh.
The theory now goes that there may have been situations when the valves were hitting the pistons prior to all this causing the thrusting. This eventually may have led to the rocker breaking, and the final end to the engine.
The cams used are well known in this engine so I can't believe they are a problem, so am now looking as to how it could have happened. trying to work out if the bottom end could have jumped a tooth on the gear.
Coincidentally it died after a clutch change on the drive home. It wasn't running well at the time either, was running lean. Thoughts are that the engine may have been rotated backwards (quite possible) and somehow jumped a tooth. Looking at the setup though, just can't see how it can as the tensioner has a reverse lock to stop it going back, is spring loaded etc....
Basically my 2000mile engine has only the rods as salvagable! sad sad sad ....
Jeff
RE: Piston thrust face scuffing, Eagle rods?
RE: Piston thrust face scuffing, Eagle rods?
FYI, it was a low rpm death, about 3000rpm or less. Was coming to a stop, foot on clutch, bang.....
I then cranked again to diagnose the problem to do more damage. I regret doing that, but I couldn't be sure what was going on.... I know now :)
RE: Piston thrust face scuffing, Eagle rods?
I would take a very good look at your piston clearances, where they are measured, and how consistent the pistons and bores are. The recommended clearances for forged pistons are dependant on which alloy they are (big difference), added clearance for boost, etc. Combine a slightly tight fit, with a little lean mixture, different cooling on each cylinder, less oil throw off some journals, or a tight pin, and you could easily have what you are seeing.
RE: Piston thrust face scuffing, Eagle rods?
Is it a radial engine with the side thrust on the piston being generated from torque reactions on the compound rod big end cap.
jmeager
Sorry if we hijacked your thread, but turbododge is spot on. get your clearances right for the materials, power levels and manner of use for your engine.
Also check your piston to valve, valve springs for tension and coil bind, valve stem clearance in guide, cam timing etc. Valve imprints on pistons are NOT a good idea.
Also, ensure your oil is of adequate quality and at acceptable temperatures
Regards
pat
eng-tips, by professional engineers for professional engineers
Please see FAQ731-376 for tips on how to make the best use of Eng-Tips Fora.
RE: Piston thrust face scuffing, Eagle rods?
Looks like you're the only one who has any interest or is willing to guess! Anyway, the engine wasn't a radial, but it DID have a master/slave rod arrangement. But that wasn't a factor. What happened was that one piston out of the 20 started to seize, because of the use of a particular oil. This engine (and another at the same location) had a history of piston seizure problems that was hard to fix, but once they switched to a diff. brand of oil all was OK. We have 6 of these engines, always run on the "good" oil (made by Shell).
Anyway, when the pistons start to seize they frequently ignite the crankcase oil vapors, causing a crankcase explosion. All big diesels have pop-off explosion doors so it's no big deal unless you're standing nearby.
Now, picture this: One piston starts to seize, the vapors don't ignite, and the other 19 cyl. say "screw it, we ain't quitting". Given strong rods, the seizing piston has no choice but to keep moving. But now, on the power stroke, most of that downward force ISN'T loading the thrust side--it's just trying to help shove the slug straight back down as the rod PULLS it! But there's hell to pay on the compression stroke on the compression-loaded face, as you can well imagine.
RE: Piston thrust face scuffing, Eagle rods?
I have been reassembling the engine over the last few weeks, measuring everything as I go - no assumptions that the factory got things right etc.
Interesting fact 1. Crank stampings for journal diameters, mostly wrong. This resulted in extremely tight main clearances.
Interesting fact 2. After now undertanding how the Eagle rods use excess side clearance as a means to allow more oil to the bores (as they don't have a thrust squirter), I actually measured this. Woops. This explains the wear on the piston!!!! Cylinder 4, the most worn one had half the side clearance of the rest of the cylinders.
So there it is I hope. I think I can safely say that I have explained the wear.....
thanks for the help.
Jeff
RE: Piston thrust face scuffing, Eagle rods?
Metalguy - thanks for the interesting tangential discussion. I'm guessing that a 10 or a 12 would be slightly more likely to see this sort of thing than an 8, as might short rod/long stroke configurations?
Norm
RE: Piston thrust face scuffing, Eagle rods?
Repeat the ATF-soaked paper towel wipe step as many times as it takes until you stop picking up residue on the paper towel.
Didn't want to leave open any questions about how much of the procedure was to be repeated.
Norm