fragile J motor

A lot of people say that the 81 and later J engine is fragile. I never hear why a nd I would really like to know.
Thanks Tom

Well, Tom, when you get a bunch of folks who share a common interest but have limited first hand knowledge, when something gets said, there will be those that take it as gospel. The J motor is pretty much the same motor as the earlier 903/1015cc motor except the valves are a bit bigger and their ain't an upper idler assembly for the cam shaft (was replaced by a guide), a hyvo cam chain and a number of other small changes. I doubt the J motor is any more fragile than any of the 903/1015.

I would guess this fragile tag came from the boy-racer bunch. They flog an engine and abuse it and if it blows up pretty much the same way each time, the part that caused the engine to blow will be picked out as the culprit. The same engine, on the street and used by a sane person may never have an issue. I would guess folks have you worrying unnecessarily... keep in mind the cop bikes which endured hard use have the J motor (82 to 95).

Thats pretty much what I thought.
Thanks George

I just called them fragile from my own experience and what I read in magazines back in the early 80s. When the J was introduced it was the fastest KZ1000 to date, but the engine was lighter, and lighter duty made to make it lighter. I bought a new GPZ1100 in 1982 and just loved it, but the top end was rebuilt under warranty twice in the 18 months I owned it. Granted I did ride it 24,000 miles in 18 months, but still a big disappointment in the engine reliability. My dad bought a new 1000J in 1981 and hardly rode it, put 4000 miles or so on it, had engine problems too. Cycle World did a long term test on a 1982 GPZ1100 too and in 15,000 miles their comments was "it's 1 second slower in the quarter mile then when new", "did not age well". Everyone read of the oil burning and fast wear rates, rebores and new pistons were pretty much the norm by 10,000 miles. That's where I said fragile from. I wasn't a racer either, I use my motorcycle for everyday riding and long tours across the country. For the long miles, the older design was much more bullitproof. Like I say this is only my opinion from what I've seen firsthand and read. I'm sure there are many that had better luck and I'd love to own a GPZ1100 or a KZ1000J again, but I wouldn't take any long trips on them again.

i never had any problems with the motor on my gpz when i got it in 84,it was the damn fuel injection that i couldnt deal with!:laugh: but theyve come a long ways with fuel injectio so now adays it would be pretty easy to solve.

What the racing community found was that the crankshaft needed a "Thrust washer mod". Also the cylinder head casting was weaker. This was never a problem until you dual plugged them and then milled them for max compression. They would split down the middle like a log. You have probably seen some old race heads with gussets welded between the cam banks.

When we were doing the top fuel thing with the late Elmer Trett, we knew to stay away from those heads. Used the old style KZ until the billet head was finished.

Jay

billet head that sounds nice.
cheaper than a plum turbo!

APE Jay wrote:

This was never a problem until you dual plugged them and then milled them for max compression. They would split down the middle like a log. You have probably seen some old race heads with gussets welded between the cam banks.

When we were doing the top fuel thing with the late Elmer Trett, we knew to stay away from those heads. Used the old style KZ until the billet head was finished.

Jay

I don't mean to hijack this thread, but the subject was brought up.
Should I stay away from dual plugging my J?
I was going to post a thread asking who still dual plugs a KZ or J head. I'm not going racing, but just thought a dual plug head will let me run cheap s&%t fuel without detonating. I need to stick with high test now. Any thoughts on this?
Stephen

What is the thrust washer mod? What parts are needed or who will do it?