Topic: 350F and 400F parts compatability

[fixahonda]

I am going to have to do the headgasket in the 350F soon since it seems to be getting to the point where the paper towel in fin trick isn't working so well anymore. I figure while it's apart, maybe it wouldn't be so hard to go a few steps further and replace the cylinders, pistons and head with the 400F parts (as well as the jets in the carbs).

So far I've found that the crank and rods are the same part numbers and the cylinder base gasket is the same PN as well. What is different is the O rings that go around the sleeves at the base. They are larger, obviously, because the sleeves are larger.

I was wondering if anyone knows if the case is cut out large enough so that I could just drop the new cylinder assembly in there or would it have to be machined out to accept it.

My engine is in perfect shape other than the leak so if it turns out that doing this is going to require a complete tear down I'm not going to bother.

[ttr400]

Yes you can fit the complete 400F top end to the 350F but as you have asked the top of the crankcase has to be enlarged to accept the 400F sleeves, it can be done with a dremel. Also the front 2 center head studs on the 350F are too long.
CB400F studs from top of case= 115mm
CB350F = 130mm
you would have to make some custom studs as the 400F thread at the case end is M10 and the 350 is M8.
Do it it sounds harder than it is.

Kevin

[heffay]

if you need 350f engine parts i've got them for you... parting out one of my 350s to fund my 400f race bike. 

[mlinder]

May as well drop in the entire 400 engine... 6spd trans...

[ttr400]

There are a few ways to do this, one is to fit the 400F sleeves only to the 350F block, fit 400F size valves and away you go. bit of a sleeper and keeps it looking stock.

I have also done one motor with the 400F bottom end with close ratio gearbox and a 350F top end with 1mm over size SS valves.

Kevin

[fixahonda]

Thanks for the answers guys.

It looks as though it's a bit more work than just swapping the parts back and forth. I'll probably just end up doing the gasket and call it a day.
Even if it's only mild dremel work to the case to remove the material I don't think it would be too good of an idea to do it with the case still together. I don't want to end up with any bits in there.

It's basically my only form of transport at the moment so having it down for a few days would be a pain in the butt. I was just curious if it would be a direct swap while I had it apart to fix the leak.

I will say that a properly maintained SOHC makes a great daily rider. I was just hoping to give it a bit more idiot avoidance power for the hectic freeways around here.