ALT125 and ALT185 Bore and Stroke

[atcmatt]

Hey legends, just wondering if anyone knows the difference of these two models in regards to the top end. Do they share the same size stroke but just have a different bore and piston size? I have a 185 that I just purchased with a trashed cylinder (cam chain has wore through the side from being mis-adjusted). It came with a 125 complete motor, unsure of its condition but doesn’t seem to go through gears too well.

I’m wondering if I can swap the 125 Cylinder & Piston, Head and rocker cover onto the 185 bottom end.

Thanks for any help, I know these are rare and unpopular beasts but any help is appreciated.

Matt

[shortline10]

Can’t image your going to get to many replies as those are pretty scarce machines .

I would start off by measuring the cylinder heights and cylinder stud spacing first .

If that matches up pull the heads and check the piston wrist pin sizes and if those match up it might be doable .

[atcmatt]

Thanks for the reply, yep that was going to be my next port of call. Just wanted to leave the 125 motor as ‘unopened’ but I’ll just do what I gotta do. Cheers.

Matt

[Shep1970]

Here's my notes- "if"u can read them" or they might confuse u even more...crank length and cams are different from 125 to 185.
265511
and there sideways too....grrrr
shep

[350for350]

Well, going by Shep's notes, it looks like you'd have a stroked 125 in you can do the swap. Of course, that may lead to issues like valve and piston contact so you's have to be extremely careful. Maybe it would be best to put the 125 on the 185 frame until you can get the 185 fixed.

[atcmatt]

Hey Thanks Shep. Looks like that’s all I need to know. Not a direct top end swap. Will maybe look into getting a used cylinder and having this one repaired. Thanks again.

Matt

[shortline10]

Might still be doable , just measure the cylinder deck heights , he doesn’t mention that in his list . Piston deck height might make up the difference in the rod length .

[atcmatt]

Yeah that is a good point actually. I’ll have to take some measurements. Started to tear down the 125 today and it’s just such a nice unopened original motor (filthy externally though), so I stopped at taking the head off. Thanks again for your replies.