My 20 year old engine is on it's last legs/bearings/whatever. I've kept it going with parts from a later engine, probably 10 years old. Mechanically, the two engines are identical so it seems.

I've got another engine, also ~10 years old, that I've just put back together. I note that the connector blocks on the generator/ignition pickup are different. Rather than hack off the connectors and wire up the new engine to the old loom, I thought I'd just use the whole engine casing/cover from the old engine mounted to the newer one. (The casing houses the generator and ignition pickup.) I will need to look at the magneto thing, to see if they are the same I guess.

Also, the newer carb has a single eletrical spade connector and the old one doesn't. Again, to keep things simple I will re-use the old carb. No idea what this connector is for; a wiring diagram would help I suppose. (Yep, I've done all my recent engine repairs/rebuilds without a manual; and I wonder why it's kn*ckered!)

Anyone tried this swop before and have any useful tips or comments for this model?

Had a chance to take a closer look last night. The generator and ignition pickup on the two engines are completely different! Both the stators and the flywheel are totally different, so my only options are:

1) Swop the flywheels, keeping the old configuration.

2) Swop the wiring loom, CDI, reg/rectifier and use the new flywheel/generator.

My initial inkling is to swop the flywheels over; I did try and remove the old flywheel with a 3-leg puller, but it wasn't having it. The flywheel is threaded, so I suspect I need a "special Yamaha tool" to insert and tighten to remove it. (Or maybe a suitable bolt would fit in the thread? I didn't have any to hand.)

I didn't look to closely at the wiring loom; I note that the CDI and reg/rectifier have different connectors, hence the need to swop the looms out. But I didn't check to see if the old front part of the loom will mate with the new back part. (I was assuming that the loom I have is just for the main part of the bike and there is a connector separating the front & rear looms.)

I guess Mr Yamaha deemed it necessary to change the charging and ignition systems. Doh!

After ordering a flywheel puller I was finally able to complete my engine swop. The replacement engine keeps the flywheel, flywheel engine casing and carb. (The newer carb is similar, but has a wire attachment that the original carb doesn't. Not sure if this connection is a heater or sensor, but my loom has no wire for it.)

It started fairly easily too; I've not done any road test yet, but the biggest difference I noticed was the noise. The replacement engine is quiet; by comparison, the other engine sounds like its full of gravel! I'll take it for a test run and then treat it to an oil change. (Looking forward to it! Hoping it might be a bit faster too.)

Big thanks to sr125shell for finding a puller for me.

After ordering a flywheel puller I was finally able to complete my engine swop. The replacement engine keeps the flywheel, flywheel engine casing and carb. (The newer carb is similar, but has a wire attachment that the original carb doesn't. Not sure if this connection is a heater or sensor, but my loom has no wire for it.)

It started fairly easily too; I've not done any road test yet, but the biggest difference I noticed was the noise. The replacement engine is quiet; by comparison, the other engine sounds like its full of gravel! I'll take it for a test run and then treat it to an oil change. (Looking forward to it! Hoping it might be a bit faster too.)

Big thanks to sr125shell for finding a puller for me.

Hi, well done with the engine swap . The wire attachment is for the carb heater - not available on earlier sr125`s (pre `97 I think). Glad to be of help with the puller. Cheers, Shell.