I purchased a motor for my XT600E but despite advertising it was actually an XT550. The engines are different in several ways, but after some research and some interesting trials, I have concluded the 550 is a bolt in replacement with relatively minor modifications required to make the swap.
Matches between the 550 and 600 engines:
- intake port configuration; use the same carbs if desired
- exhaust port configuration; use the same exhaust header if desired
- chassis mount points; use the same engine mounts
- clutch disks; steel and friction plates match, as well as springs, but 600 requires an additional wave spring not used in 550
- oil feed line; oil feed inlet is designed and located the same on both models
- spark plug; threads match between both, and access to the plug for removal is equally absurd on both
- camshaft; cams are interchangeable between models and (if I remember correctly) have identical lift and duration specs
- oil filter, cover, and o-rings; direct match
- fasteners; same quantity and dimensions, more or less, throughout
- ignition system; 550 uses CDI* and 600 uses TCI. none of coil, ignition box, or harness are interchangeable without internal modifications
- oil reservoir and return line; 550 uses an external reservoir, whereas 600 returns oil to in-frame reservoir. return line is different length and construction
- engine L/R side cover and gasket; close but not interchangeable
- countersprocket; 550 uses an offset spline "key" whereas 600 uses a centernut
- countersprocket alignment; 550 countersprocket is positioned a few mm inward, toward the center case**, compared to the 600
* As a side note, I was initially befuddled by a faulty ignition. To save money over a $500 factory replacement I tried the Wayne Gum ignition referenced in the 1st post
. I could not be happier with how it runs, and the wiring matched my harness perfectly. Highly recommended at one 1/4 the price.
**The countersprocket alignment did not appear to generate additional chain noise or movement in operation, nor difficulty in adjustment. However, you should expect the chain to stretch faster than stock if this difference is not reconciled at the rear hub. Smaller than stock countersprocket may compound this issue.