305 Racesaver sprint piston scuffing issue

[victorymachine]

Hello to all,

I'm having a piston scuffing issue that I would like opinions on the cause. The engine is a 305 Racesaver sprint car engine. The induction system is Hilborn mechanical injection with Methanol being the fuel. The engine has scuffed the skirt of #2 piston twice now. The first time was from a previous shops build, it came to me for a rebuild with #2 very scuffed and pumping oil. The rest of the pistons looked fine except for the wear from 3 seasons of racing. I rebuilt the engine, going from .040 to .050 over pistons. The engine is scuffing #2 ( and only #2) after only three nights of racing. This is my first Methanol injected motor and would like some confirmation from you guys about what caused the scuffing? Thanks in advance for taking time to look! Feel free to ask for any other info or pictures you may need.

Major thrust:

major thrust1.jpg

Minor thrust:

minor thrust1.jpg

Front:

front side.jpg

Rear:

rear side.jpg

Bore Major thrust:

Cylinder major thrust.jpg

[pamotorman]

did you check the water jacket in that area to make sure it is clear and coolant circulating ???

[roc]

Any chance that cyl #2 is running leaner (partially clogged fuel nozzle or something similar)?

[Dan Timberlake]

Got pictures of the undersides of the piston domes, and the top sides, and spark plugs.

Any data acquisition ?

[jac mac]

First thought that comes to mind is the #2 cyl is being over cooled...too much coolant flow to that bank.

Is it always after the third night of racing, if so is sitting nose down on a trailer after the meets and due to injector hose orientation getting wash down in #2. Not getting x-fire from #7 in ignition system.

[pamotorman]

First thought that comes to mind is the #2 cyl is being over cooled...too much coolant flow to that bank.

Is it always after the third night of racing, if so is sitting nose down on a trailer after the meets and due to injector hose orientation getting wash down in #2. Not getting x-fire from #7 in ignition system.

the stock water pump should have the coolant by pass hole plugged if that is what you are using. the sprint car engines I have seen feed the coolant into the center of the block not in the stock front location

[englertracing]

is there any way that thing isn't getting as much oil as the rest?
is there methanol in the oil?

id think rich and not lean, if it went lean id expect it to remove the top ring land. and the ring lands to show more sings of contact than the skirt
you should have him send the injection out for balancing.....

[user-23911]

I've seen that on diesels quite a lot. Often in that case the piston has got too hot due to the diesel injector leaking so it has the same symptoms as a petrol engine which has been having pre ignition problems.

[user-612937456]

Running rich washed the cylinder down I would be be critical of a number 2 injector. If it wasn't overheating problem I think you would see more evidence of heat on the piston with regards I'm not seeing the inside of the pistol that is. I think it's just lack of lubrication from fuel getting by the Rings keeping a cylinder wash down. Unless something is causing lack of crankshaft splash on that cylinder wall

[MadBill]

I'd expect wash down to cause ring friction to wipe out the cross hatch, which hasn't happened. An underside shot of the piston to look for brown or black coloring would help, but I vote for lean mixture, likely a partiallly plugged injector.. For a conventional SBC firing order, #7 is the loser for cross fire from the #5 wire.

[user-612937456]

Also I couldn't help but notice the two compression rings and one of the oil-ring retainers are close to being lined up on the thrust side piston skirt which would contribute 2 fuel getting Past the rings side of the piston

[victorymachine]

Thanks to everyone for responding!

did you check the water jacket in that area to make sure it is clear and coolant circulating ???

During the rebuild, I half filled the block with ROKBlok block filler. Before filling the block, I thouroughly cleaned the entire water jacket with muriatic acid.

First thought that comes to mind is the #2 cyl is being over cooled...too much coolant flow to that bank.

Is it always after the third night of racing, if so is sitting nose down on a trailer after the meets and due to injector hose orientation getting wash down in #2. Not getting x-fire from #7 in ignition system.

the stock water pump should have the coolant by pass hole plugged if that is what you are using. the sprint car engines I have seen feed the coolant into the center of the block not in the stock front location

This engine has the bypass plugged and the feed rerouted to the center of the sides of the block, just as you described.

Got pictures of the undersides of the piston domes, and the top sides, and spark plugs.

Any data acquisition ?

No data acquisition. Pictures as requested:

#2 top:

#2 top.jpg

piston bottom:

piston bottom2.jpg

piston bottom 3.jpg

#2 plug:

#2 plug.jpg

#4 plug:

#4 plug.jpg

#6 plug

#6 plug.jpg

#8 plug:

#8 plug.jpg

Some details I forgot to mention earlier. I broke the rebuild in on a test stand with a carb intake on gasoline. Ran great no issues. Cut open the oil filter afterward and looked fine, nothing abnormal. Switched over to the injection and put it in the Sprint car. We went racing with a conservative tune. Motor had no heat in it after the heat race so we increased the pill size to lean it out some, two sizes if I remember correctly, still no heat after running the main. Changed oil, cut open filter, all good. 2nd weekend we increased the pill size by another two and the car was showing 170 as it was pulling off the track after the heat race. Ran the main that night and never saw more than 180 degrees. 3rd weekend - pilled it up another 2 sizes - temps now around 200. Changed oil, cut open filter and saw aluminum in the filter. Tore down and found the scuffing.

From the scuffing troubleshooting guides I can find, the way the skirt looks seems to point toward lack of lubrication, but shouldn't it have scuffed early on when we were running it rich then??

The aluminum in the filter didn't show up until we were leaning it out, so as mentioned, is that nozzle plugged or flows the least and leaned out #2 first?

Thanks for the help guys. Much appreciated!

[englertracing]

Do the main bearings all look the same?

[induction apprentice]

I agree with all the suggestions so far. I have no magic answer? My knee jerk is usually to blame the tune-up first. But it does not look like it got to hot despite the larger and larger pills. Definitely does not look like it had to much timing and I don't see any obvious signs of detonation? I was also leaning toward a clogged injector. But they all look pretty similar.

Sooo. My kick at the can is a long shot. But maybe it is worth bolting the cylinder head back on with the old gasket. Flip the block upside down and check the bores from the bottom with a dial bore gauge. I have seen some pretty radical s_it go on with bore distortion on sbc and stud kits. It may be that cylinder is tightening up with the head bolted on as compared to what happens in the hone with a torque plate. The head can be a game changer compared to a torque plate. Even if the torque plate is the same material.. That with a leaner mixture combined might just have been enough to tighten that hole up?

Lastly. a total long shot also. But maybe hot plate a few pistons including the offender and see if the expansion geometry is similar?

[Cogburn]

My guess is that the engine was not properly warmed up and the piston ran out of clearance from expanding quicker than the block.