Small end rod wear

[Alain2]

I am doing winter maintenance on my 1977 RD400; fixing a possible head gasket leak and removing carbon deposits.

I don't know if I got lucky or not, but I caught this rod relatively on time, before total destruction anyway. The associated cylinder shows 0.0005" more taper wear than the healthy one, but I guess it may just be coincidental.

The worn side was showing a bit richer on the piston wash and I suspected a possible head gasket leak. EGT was cooler than the good side, but CHT was hotter than the good side, again these maybe coincidental based on timing (points), carb tuning and other variables.

Mileage on the crank assembly is unknown. I'm getting a new crank with Prox rods.

[pidjones]

Lucky catch before more damage.

[Alain2]

I'm wondering how much mileage I had left before self destruction.

[rodneya]

Ive never seen a pin wear where it sits inside the piston before. Do you know what small end bearings were in there and for how long.
Are there any signs of detonation on the piston or head?

[Alain2]

Ive never seen a pin wear where it sits inside the piston before. Do you know what small end bearings were in there and for how long.
Are there any signs of detonation on the piston or head?

There is no wear on the pin except for the pitting at the bearing. It looks way worse than it is on the picture. The small end bearings are Yamaha, approximately 1600mi on the bearings and pin. I don't know the mileage on the rods, that is part of the reason why I was doing maintenance on this engine, I had to keep an eye on it. All my other Rd I built were done with a new crank.

No sign of detonation on the piston. There is some minor pitting in the combustion chambers, but it was already like that.

[m in sc]

that rod looks like a bearing sat in it a long time and pitted it. Ive seen that before. then you rebuilt it. Id bet its 'old' damage.