Top End swap out.

Alright. Ive got a good engine with a reeally good clean top end was never seized but bottom end is junk.

And ive got a good motor that runs barley with very low compression and mine as well cut it out before i hurt the bottom end.

My plan is to take the good top end off of the engine with the crap bottom end and put it in the engine with the bad top end and awsome bottom end.

Both engines are same year and both are yics. Can this be done and what else may i might need besides gaskets and im planning on putting new rings in while im at it.

 

In theory, it should work. Are they from the exact same model and year? My knowledge of engines comes mostly from cars, where manufactures tweak things like the diameter of oil holes and air port sizes over time. Maybe some XJ guys can jump in and say if any 650 YICS head is the same as any other.

When swapping heads on a big motor, it is important to make sure both the head and engine block are perfectly flat. A machinist will have the tools to measure this. I don't know if XJ heads flex more than car heads due to the greater temperature differential in an air cooled engine or if it's not as big a concern as they are smaller than car heads. Heads that have been abused can warp over time, and must be machined back flat. Normally the engine has to overheat for this to be a problem. Additionally, you will want to look at the valves, valve stems, etc. while you have them clearly visible. It is easy to fix stuff now, after assembly it is a pain. There is nothing worse than putting an engine back together to learn it wasn't the heads, but rather the rings that were bad. Normally if I have the head off an engine, it is worth the money to have a machinist go over it. Last heads I messed with were for a 231 V6, and all the hot tanking, planing, valve grinding, and reassembly was $200 for both heads. If the heads are in top shape, you can probably skip the machinist, but if they are questionable at all I wouldn't. I'm thinking a valve adjustment and carb sync is absolutely required when your done.

Get everything as clean as possible. I'm talking "eat off it" clean. This is the only way to get a good seal.

Buy a click type torque wrench if you don't have one. At a minimum $20 from Harbor Freight, or $80-$100 for a pretty good calibrated one. Find the torque specs and bolting order, and follow it exactly. I seem to think the head bolts on my XJ550 are hex, so you will need a socket that connects from hex to 3/8" or 1/2" drive.

Engine work seemed intimidating to me when I started, but now it's the fun stuff. Carb's are an exercise is precision, and drum brakes are an exercise in how much can a person bleed before something is fixed. Compared to either carbs or brakes, I'd rebuild an engine any day.