Machine Builders Network+ Forums Machine Builders Network General Discussion Anatomy of an engine failure

This thread covers the teardown of a 79.5cc Chinese clone engine that was used on a small 1500W generator. Failure occured after some 4,000 hours of operation.

Engine had been treated with a one time treatment of one heaping teaspoon of pure molybdenum disulphide powder on third oil change. Oil was changed roughly weekly, but sometimes not for a couple of weeks.

The actual failure was caused by the rivets on the cam that hold the decompression pall worked loose. This alowed the pall to move sideways. Edge of pall basically beat the crap out of the cam drive gear on crankshaft. Distorting teeth of gear bad enough for gear teeth to bind up.

What is truly remarkable about the engine is the pristine condition the cylinder, piston and connecting rod bearing are in after 4,000 hours of operation. The only other preventative thing done to rngine was the addition of a drail plug magnet to collect any loose wear particles. Magnet was eiped clean with every oil change. Only cleaning done on thid teardown was drain oil and wipe residue with shop towels.

Here us link to photo series: Moly Treated Engine Teardown

Doc

WoW that's pretty nice looking for 4000 hrs

I have heard that some of them rivial b7s and kohler! I never had one so don't know! Yours sure looks good!

It may be understandable that I have become somewhat evangelical about molybdenum disulphide usage in all my engines.

Another remarkable thing about the torn down engine was at the time they were selling for about $90. When I realized that the Harbor Tool engine was basicslly identical to those being used on the 1500W generators I bought one to replace the engine on the cheapo generator. Not actually a bargain in terms of labor. The exchange requires a complete dissasembly of both engines and total reassembly of new engine using only the tapered shaft crankshaft off the old engine. Total time for swap out about 9 hours. (At least for me.) Reason heads have to come off is that the govenor drive gear hits the skirt of the piston, preventing crankshaft removal without pulling head to move piston out of way. Otherwise swap out could be accomplished in far less time. (I guess part of that 9 hours was due to farting around trying to remove crank without pulling head...)

Anyway, when all was apart I took the time to mic the connecting rod journal on both new and old engines. Verified that the old crank was within a thou of the new one. Not suprising given connecting rod being made of aluminum and crank of cast or forged iron. So virtually all wear occurs on conecting rod bearing.

The swap out does sacrifice the low oil shut off switch as the HF engine doesn't come with one. Not a big loss. In exchange the HF engine comes with a full metal cam. (Unlike the original gen engines which were nylon and typically failed at about 1050 hours (+/- 50).) Guess I've swapped out about three of the engines so far. Have another waiting for me right now... if I ever become mobile enough again to perform the swap.

Doc

sounds like you took these engines beyond the curve..that moly is the hot ticket for flat tappet engines,I use it in all my small lister petter generator engines it really does a nice job for some extra insurance on startup wear..the listers get 15K hours no problem before teardown(2cyl and 4cyl water cooled diesels) I have been adding to my john deere gen drive engines too..gotta look into getting just the raw moly like you have and dosing it myself instead of the snake oil type plastic containers premixed with oil.

Pricey up front, but basically a lifetime supply at teaspoon doses. Pure Moly Powder
I got a 500gr (1 lb) bottle when I was in high school. Just ran out and had to reorder last year.
Doc