IAME 175 SSE Rod lower end inspection

I’ve got an IAME 175 SSE that I have run all season, about 10 club events which I think is about 10 hours of run time. The engine is probably not ready for a crank rebuild yet, but is there a way to gauge how much life might be left in the bottom end. The info sheet from IAME says to replace the rod when there is .0005in ovalization. Have any of the smart and talented folks on this message board been able to measure this with the engine assembled? I’m a Tool and Die maker by trade and I have the proper indicator to measure this small increment but I haven’t had the cylinder apart to attempt this yet. How much clearance should I see in the lower rod bearing. I think with the cylinder off and crank at top dead center I could measure play with the rod vertical and then rotate the rod, but not the crank, almost 90 degrees and check clearance again. The difference in readings would be ovalization. Am I crazy or could his work? What are other members experiences with checking rod bore ovalization with engine assembled? Thanks for your input.

10 hours is a bit of a toss up. In my experience with the 175 SSE, I’ve had rod assemblies that I’ve ran for 20+ hours without issue, and others that have failed around 10+. If you’re easier on equipment then longer intervals become more likely. Also depends on what oil you’re using and mix ratio.

I see what you’re onto, but I’m not sure it’s possible to completely isolate the portion that you’re actually trying to measure, and do so accurately. In theory you could be capturing play in the lower rod bearing itself, as well as the main bearings. I suppose radial play of the con rod could be a proxy, but I’m unsure what “good” would be.

@Charles_Kaneb recently mentioned that he put 40+ hours on a bottom end, so maybe he has some secrets he can share!

I agree with the above, you can’t measure ovalization from the outside. My suggestion is to inspect the bottom every time you do the top by checking lateral play, visually look into the rollers and rod to detect any heated spot or damage, and vertical play by feel (if you feel any, you are past the point of no return) with the engine assembled. If all looks good, you are good to go. Scheduled time for a bottom in a SSE is at 20 hours so at that point (or earlier if you suspect something is off), you can get a basic kit (pin, roller cage, new spacers) and send it off together with the crank to a shop for inspection. They will take it apart, check ovalization and the rolling surfaces with a magnifier and if it’s all good put it back together with the fresh needle bearing/pin/spacers so you are good to go for a while, at a reasonable cost.

Personally, I’d stick to mfg recommendations (20 hrs on the SSE) and visual checks in between, then you can calibrate from there based on what you see happening on your own engine. I’m sure it can go way past 20 hrs, but we don’t know if you are running lean to the brink of destruction or downshifting super hard just to name a few, there are tons of variables…so start safe and increase intervals if you have appetite for it and/or see no wear.

On my motor the con rod bottom end bearings gave up at 346.5 liters. I dont know was it the bearing that failed or the side pressure washer that got too thin. Doing the dissassembly I noticed the washer had folded over, taken all the side clearance and jammed the crank. The time the con rod bearing failed I used the cheapest 2 stroke oil available. That might have been the cause

I would say the engine is very reliable. Before this I had seized the engine several times. Because of my carb tuning mistakes. And ran it without coolant few times at 90-100´C. Didnt bother to split the cases - just honed the cylinder and fitted new piston.

The engine kept running just fine - my misuse didnt affect it at all. It made good power at the dyno

The cases are still good - Im doing a rebuild this winter

The only “secret” I have is not regularly running an engine with a 64mm piston to 14k5 RPM, the red light on my MyChron comes on at 12k8 and I set the main shift lights to come on at 12k. I use the exhaust spacer you sent me to have the engine come off the pipe by 13k3, and I rarely run a chaindrive ratio shorter than 1.33:1 figuring that hardly any corners are tight enough to get me below the powerband in 2nd gear with that ratio. I ran Elf HTX 909 until we hit the Great Summer Elf Shortage and then Polaris VES Extreme which seems to be very similar.

I don’t see a good way to measure conrod ovality and bottom-end wear without just rebuilding the engine. By the time you’ve got measurable radial play in the bottom end it’ll already have failed catastrophically.

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