Piston thrust face scuffing, Eagle rods?

[jmeager]

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

 

[Metalguy]

Patprimer,

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.

 

[jmeager]

Thanks Smokey. I didn't think something I left out was important but it now seems it may have been critical to the problem.
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

 

[Metalguy]

Isn't the crank OK too? Were the carbon-covered valve marks both int. and exh.?

 

[jmeager]

Yes, both intake and exhaust. Crank hasn't been checked. Please don't ruin my year more than it is already with such talk! hehehe. I'm taking it all pretty well I must say! Having just paid a heap of money to rebuild it, to do it all again. barely anything left that is usable. The machinist said the piston is on the limit of reusable. He said the taper ratio is still right. Once he measures this one against the other he will say whether he can "clean" this one up....

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

 

[turbododge]

On their V8 rods, Eagle makes them about .010 narrower than stock to allow more oil out of the bearing. They count on the extra oil to be flung on the cylinder walls instead of squirted. I think this is fine for a high rpm engine, but MIGHT be and isssue for a low rpm cruiser.

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.

 

[patprimmer]

Metalguy

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

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[Metalguy]

Patprimmer,
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.

 

[jmeager]

UPDATE:
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

 

[NormPeterson]

Hope I'm not too late to this topic, but the block-cleaning drill that the machinist who runs the shop where I get all that sort of work done advises to first clean the bores with water and detergent. Rinse the soapy stuff out; a little WD-40 helps. Then go back and wipe with ATF-soaked white paper towels, and don't be afraid to use a little force. Repeat as many times as it takes until you stop picking up residue. Clean wipes = clean bores, plus you've worked some lubricant into the surface for a measure of startup protection.

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

 

[NormPeterson]

Just to clarify . . .

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