Bros 650 in a 400 casing

[Yoke]

I have a good 650 engine that has some physical damage to the mount, and I have 2 x 400 engines that are sitting on the shelf awaiting their day. Is there any difficulties with moving the 650 over to the 400 casing? I have both of them on the table and I can’t see any issues, casings look identical. I will need to split them to be 100% but the look good. I know the box ratio, clutch plate number are different, anything I am missing?

Thanks for any advice.

[yorkshire]

Hi Voke, I have a the cases of a 400 with 600 barrels, pistons, heads and crank running, I believe the problem with the 650 barrels is the crankcase throat will need opening up for the barrels to fit. both engines were external oil feed to the heads, the parts I have used are 600 barrels, pistons, cylinder heads, crankshaft and conrods, crankshaft primary gear, clutch(slightly modified) piston oil squirters. the 650 engine parts maybe different to the 600 parts. hope that helps.

[Yoke]

That’s great information thank you, I put the two on the bench last night and I am going to start disassembly. I measured the throat yesterday and it looked identical, I’m gonna give this a try, sure it’s just scrap on a bench otherwise.

Thanks again for the input.

[Yoke]

Hi Voke, I have a the cases of a 400 with 600 barrels, pistons, heads and crank running, I believe the problem with the 650 barrels is the crankcase throat will need opening up for the barrels to fit. both engines were external oil feed to the heads, the parts I have used are 600 barrels, pistons, cylinder heads, crankshaft and conrods, crankshaft primary gear, clutch(slightly modified) piston oil squirters. the 650 engine parts maybe different to the 600 parts. hope that helps.

I measured this again and your right, there is about 1mm in difference, so the 650 wont fit into the 400 casing without a modification. If thats the only issue, I will make the adjustment.

[rpcraft]

Just throwing it out, but rather than take an engine apart to refill the gizzards and have to redo all the gaskets, why not just find someone who can tig weld and reweld the mount to "good enough"? It doesn't have to be a perfect weld surface, it just needs to be strong and close enough (I guess depending on where the damage to the mount is? Maybe a photo of the damage area can illicit some more feedback to tell you the better solution that swapping innards?

[Yoke]

Yeah that’s not a bad idea at all, I don’t have a welder that will do aluminium but it’s only half a mount that seems missing, maybe it was involved in a crash and this damaged it. I will try that instead.

At least I can confirm that the 650 barrels won’t fit onto the 400 casings without taking a few millimetres of the sides of the casings. It’s a bit mad that Honda didn’t use the same mould for a a sake of mm. If someone was interested in this setup.