Engine damage
- Thread starter flattop1
- Start date
Dan Brown
Member
The early o7 leopards were known to break a rod and throw it thru the front of the cases. But seizing pistons is more common.
Pete_Muller
Moderator
I suppose it depends where the rod breaks. In the old days (70's and early 80's) the most common rod breakage was caused by a failure of the big end rod cage... which would then weld up and break the big end apart. Also a massive failure of the piston can break the rod, but then it's usually just under the small end of the rod, from what I have seen.
Pistons are definitely the highest wear item, and the item most prone to a catastrophic failure.
PM
Pistons are definitely the highest wear item, and the item most prone to a catastrophic failure.
PM
alvin l nunley
Site Supporter
I once trusted someone(I thought he was a friend) to go through an engine " just to make sure"! It was just before my trip to Oklahoma City for the nationals in 78. Through a rod in practice. The only time that ever happened.
Last edited by a moderator:
Brian Montgomery
Member
I have seen rod and crank needle bearings come apart, makes a real neat sound before it goes thud!
Pete_Muller
Moderator
Breaking the big-end of a con-rod was not all that uncommon back in the "old days". Burco had made some big-end rod bearing cages out of bronze, and if lubrication was not that good, or the engine had a decent mount of time on it.... it would "weld up" the big end cage and break the big-end of the rod in half. I saw quite a few failures like that.
PM
PM
Pete_Muller
Moderator
I don't believe the KT100 cage has ever been made from brass. Back around 1980 when we first started turning the engines pretty high revs, the stock cages would often break, and when they did a small piece of steel from the cage would go through the engine and trash the piston and head (if we were lucky), and chew up all the ports (if we were unlucky).
I made some cages for the KT100 back then out of 7075, which were stronger, but not indestructible. The good part was that IF that aluminum cage broke, the cross section was thick enough that the parts could not escape the confines of the rod bore, so the engine didn't get trashed.
It would just slow down a touch, so if the head and cylinder was removed, it was visible that the cage had broken.
Once the bottom-located cage with thrust-washer setup became available, big end bearing failures mostly stopped.
PM
I made some cages for the KT100 back then out of 7075, which were stronger, but not indestructible. The good part was that IF that aluminum cage broke, the cross section was thick enough that the parts could not escape the confines of the rod bore, so the engine didn't get trashed.
It would just slow down a touch, so if the head and cylinder was removed, it was visible that the cage had broken.
Once the bottom-located cage with thrust-washer setup became available, big end bearing failures mostly stopped.
PM
rainman
Member
I have bent a Yamaha rod and had messed the big end cage once causing major damage on a Sudam engine, including the bore of the rod big end, but never btoken a 2 stroke rod. I do remember once upon a time we had someone stealing cans of my 2 stroke oil I had stored at my favorite track in Spain and also stealing some precision tools from my good friend who owned the track, so we refilled one of the cans with regular car oil and the dummy thief destroyes a water cooled reedjet ICA prepared by one of the best builders in Europe. Rod went through cases and even cut through the carb. He packed his stuff (well whatever was left) and we never saw him again at our place.
Pete_Muller
Moderator
Speaking of rod failures and big-end bearings...
Many years ago, when I was enduro/road racing a KT100, I was on a mission to find the best oil for the big end bearing (in my opinion, the b/e bearing is THE MOST critical item in the engine to lubricate correctly in a high-rpm 2-cycle engine).
I tried many oils over the course of a season, and came to the conclusion fairly quickly that the best way to determine what oil was doing the best job was to look at the b/e bearing rollers under a microscope. That would "tell the story" better than anything else I could find. I would split the crank after every race weekend, inspect the rollers, install a new cage and rollers to get ready for the next race.
Bottom line: after a season of testing a lot of oils, nothing seemed to lube those rollers better than the original Castrol R-40. It's a "messy" oil in the upper end, but I stuck with it for all the gasoline-fueled engines I ever raced. It's the only oil I ever used (back during that time) where the roller would come out of the engine still with a mirror finish on them after a race weekend. All real castor oils were very good, but Castrol R-40 had an edge.
Oils have advanced over the years, and there may be something as good or even better now... but I would still test the same way if I was doing a comparison now.
[your mileage may vary]
PM
Many years ago, when I was enduro/road racing a KT100, I was on a mission to find the best oil for the big end bearing (in my opinion, the b/e bearing is THE MOST critical item in the engine to lubricate correctly in a high-rpm 2-cycle engine).
I tried many oils over the course of a season, and came to the conclusion fairly quickly that the best way to determine what oil was doing the best job was to look at the b/e bearing rollers under a microscope. That would "tell the story" better than anything else I could find. I would split the crank after every race weekend, inspect the rollers, install a new cage and rollers to get ready for the next race.
Bottom line: after a season of testing a lot of oils, nothing seemed to lube those rollers better than the original Castrol R-40. It's a "messy" oil in the upper end, but I stuck with it for all the gasoline-fueled engines I ever raced. It's the only oil I ever used (back during that time) where the roller would come out of the engine still with a mirror finish on them after a race weekend. All real castor oils were very good, but Castrol R-40 had an edge.
Oils have advanced over the years, and there may be something as good or even better now... but I would still test the same way if I was doing a comparison now.
[your mileage may vary]
PM