piston wear normal? (and con rod picture)

[thedude306]

Howdy all,

I have my 208 apart to install a billet rod and remove the governor and just want to know if this wear is normal on the piston?

I've got about 40 hours on the motor with 4-5 oil changes (I think this is the 5th) running synthetic 5w30



Oh, and this is what your stock connection rod is doing to itself at max 4100RPM. YIKES.

 

[JTSpeedDemon]

It looks like you had grit in your oil!

Piston wear on the skirt is not a deal breaker, but DO check the bore. Might wanna replace the rings, too.

It's a little hard to see, but the wear pattern on the skirt is making me think bent/twisted con rod(yes that can happen). Normally, NO, piston wear is not good or normal.

And man, that con rod bore is TRASHED.

How do the crank and bore look??? I'd imagine about the same, but IDK.

Usually grit gets in the crankcase from either contaminated oil, or failure to clean around the oil fill cap.

Heck, if that carnage happened, how do the main bearings look? Cam lobes and tappets??

Check everything carefully, you may have a lot of problems on your hands.

BTW, MORE PICS PLEASE!

 

[thedude306]

Oil was VERY dirty. I figured it was the connecting rod failure that was the major cause.

The bore looks great. (cast iron on this engine) Hatch marks still there, no weird markings. The crank has some galling AL on it. I am going to polish it and see. Replacing bearings as well but they appear, feel fine.

Cam and tappets appear OK as well. Didn't get pictures.

I have new rings on the way. Ya, I didn't think that the markings are good.

 

[J.S.@SMS]

Yep, that rod's done. But what worries me is the scoring at the very top of the piston. I almost think you should lap the valves just in case. But overall I wouldn't say that the piston is to heavily damaged, though that is a bit much for just 40 hours. I've always ran Castrol GTX 10w30 conventional oil in all my stuff (conventional is plenty for these things). But you're going to have to run conventional oil for the first 3 hours, then change it, and keep using conventional until it has at least 10 or 15 in my opinion (until the oil starts to darken) then you can switch to synthetic. Synthetic is not capable of being used as a break in oil, it's too slippery and doesn't let the rings seat.

PS: for the break in, let it idle until it's up to temp, then ride it around gently for a few minutes, then get on it some (don't slam it to full throttle, but go there quickly), let it get to around 3500 maybe 4 grand then let off and let it engine break, and repeat a couple more times. The acceleration part will help to seat the rings, and the engine breaking part clears the cylinder walls of the metal shavings. I did this for the break-in of one of my predators, and it's the best one I own (it's smoother, and has more power).

 

[thedude306]

Thanks for the tips on the conventional oil and break in.. I started right off with the synthetic so that could be an issue. I did do a "break in" with both the new engine and when I replaced the cam about 20 hours ago. only about an hour on the first go with lots of RPM variation and 20 minutes on the cam per instructions.

I hope I can clean up the crank. I don't want to remove any material. Any hints/tricks for that. I will plastic gauge the new rod just to get a base line when I am done. argh

these little engines are fun! ( I really do like working on them)

 

[thedude306]

Just an update, I got the crank polished and all the parts showed up. I did measure some clearances.

Here are my numbers. Any issues with these?

Piston to cylinder wall .0039
piston ring gap .009
rod to crank .0031
crank endplay .0015
valves .004 cold

head bolts 20 ft-lbs
rod bolts 170 in-lbs
flywheel 65 ft-lbs

New rings are much better quality then the originals.

Forgot spark plug at home so didn't run it today and to oily to get pictures. I also went with a thinner head gasket

As snowmobile season is over I am looking for offroad Karts for the kids to swap the engines into. Going to look at some local options on the weekend.

 

[Brianator]

Diesel oil is great for initial break-in so I've been told by a racecar engine builder. The break in procedure JS outlined is spot on, the pressure from acceleration forces the piston rings out against the cylinder wall(s) and aids in seating them. Proper break-in is key to a solid running, long lasting motor and that goes for ALL motors big and small (from RC glow engines to big block automotive racing motors)