400 conversion to 440

Hey riders. Ive got a build on my hands. I bought a bone stock 79 ltd. im gearing it lower to have speed with less rpm. Im wondering if i can put a 440 top end (pistons cylinders and valvetrain) onto my 400. Will it simply bolt up together

How about an introduction of you and your bone stock bike.


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Garrettporter wrote: Hey riders. Ive got a build on my hands. I bought a bone stock 79 ltd. im gearing it lower to have speed with less rpm. Im wondering if i can put a 440 top end (pistons cylinders and valvetrain) onto my 400. Will it simply bolt up together

1) Welcome aboard!

2) Respectfully, that is not "bone stock". The exhaust is an aftermarket replacement, and from the look of the headpipes your engine is running very lean and therefore a) hot and b) down on power. Before you start thinking about a conversion to 440cc I recommend you get the 400 running properly first. There is a lot of guidance available in this forum, and the first suggestions you will likely get will be to get a factory service manual and then adjust the valves.

Good advice as always here. Get the bike running properly before assessing the need for more mods. Those header pipes are running scary hot so figuring out why would be high on the list of things to do.

Lowering drive ratio = higher gearing = lower revs for the same speed....

Respectfully, that is not "bone stock".

He said he has a build on his hands, so the photo is probably after he's already made some changes.

I am running lean. That's because the carbs have aftermarket needles and the floats need readjustment for them to fine tune them. Ill have to look into the valve twist on them. So thank you for that. And ive included a pick of the bone stock before i made changes. The pipes are stock. The baffle pipe was completely removed and left cyl header moved to rest with the right. Its geting full exhaust this winter, raked and a springer. Any more advice is always helpful. Thanks

I am pretty sure that the 400 uses a roller cam chain and the 440 uses a hyvo chain, which means swapping the crank. I have read that the 440 liners are too big to fit into the 400 crankcase without modifying the crankcase. Not a drop in deal.
As stated above, those stubby pipes and the lack of the factory air box setup are robbing the engine of much of its power, and the dangerously lean condition will do serious damage to the engine.

I am pretty sure that cute blonde was not factory equipment :whistle:

The pipes do need to be longer. Do you think that would cause part of the heat problem at the headers? And it does have the air box. I hate that thing lol.

I'm confused. Did you chop off the pipes right where they cross so they are just about 6 inches long and then dump straight down?

No i took the bugal looking rear part of the exhaust off so the pipes are ending under the bike about where the front of the seat is