SRX 700 piston melt down

S

SRXMIKED

New member
Joined
Feb 8, 2011
Messages
3
Age
48
Location
Wisconsin
OK, here is my story. A few months ago a purchased a 1998 SRX 700 with a blown engine. Basically the motor looked like a gernade went off in it. The piston on the stator side was seize up and had broke off the connecting rod. The middle cylinder was also trashed, i think it may have sucked up fragments of carnage from the first cylinder. The case was also cracked in three spots. I figured the problem was that the crank had moved out of timing because that year was notorious for that. Upon further examination I saw that the crank had been welded and rebalanced per the warranty. So I basically have know idea why the engine smoked. I picked up a used complete lower crankcase,crank,and rods off ebay that was off a running sled with 3200 miles on it. This crank has had the warrenty welding and balancing done as well. I also picked up two jugs and pistons from that same running engine on ebay. I was able to salvage the jug and piston on the PTO side of the blown engine. I also reused the oil pump from the blown engine. I bought all new rings for all three pistons and a gasket kit. I assembled the whole engine and put it into sled. I made sure to take my time and clean everything to surgical standards. I used all the torque specs in book to reassemble engine. I also replaced all oil and fuel lines on the sled. I took the float bowls off the carbs and cleaned all the needles, seats, jets, and passages i could find. I also put in brand new boeysen reed valves and took apart all three power valves cleaned and replaced seals. I topped off the oil resevoir and put in 3 gallons of fresh gas. I did however premix the 3 gallons to 32:1 so I could make sure the oil pump was working. The engine started up on the 4th or 5th pull. I ran it for about 15 minutes to warm it up and kept an eye on coolant level. I then took it out for about a ten mile ride and it ran great. The next week I took it for a 30 mile ride and it also ran great. The oil level in the resevoir was going down so I figured the pump was working. By this time I needed to put in gas. I filled it with premium gas and hit the trails with friends. About an hour into riding the sled started to backfire. I pulled over and checked the plugs. They all looked ok so i started pulling wires one at a time while the sled was running to find out which cylinder it was. I found which cylinder it was and realized there was no compression. Towed sled home to find a melted piston and a scratched up cylinder. The piston was melted on the exhaust side of piston. This was the piston and cylinder the I was able to salvage from blown engine. I got new parts but I need to find out why. If anyone can help me out I would appeciate it. Are Carbs running lean? Did putting in boeysen reeds make it lean with stock jets? Is it lack of oil?

Thanks for help
 
Last edited:

Post pictures of the damaged parts to help the engine gurus diagnose the problem
 
Hm, how about the fuelpump?
And you should make sure on how much oil it´s using!
When I checked mine (set on the richest setting) I found out that it only used 25-30:1 8-/
Now I always premix and check everytime I fuel up and sometimes it suddenly used 60:1...
 
Update on melt down. Found that the pevious owner had put in one size smaller jets. And he had the #1 cylinder and the #3 cylinder jets mixed up. The #3 cylinder is suppost to have a different sized jet than the other 2 cylinders. He also was running br9es plugs which are hotter then the br10ecs it is suppost to run. I think these three things all played a part in the melt down. The only other thing I want to check is the oil pump adjustment. Does anyone know the correct way to adjust the cable? Thanks
 
The problem wasn't the plugs. It was that lean carb jetting that did it in. If oil pump wasn't working, you'd be cooking bearings first, before a piston.
 
You must log in or register to reply here.


Back
Top