350x big bore question? MR ATC!

[3WheelsForever]

Mr ATC, Im wondering about the xr 500 conversion. You said that you use the xr sleeve itself in the 350x cylinder. Does anything else have to be done to the engine other than having the cases machined? What year of sleeve can be used? Thanks.

[Black Sheep]

79-82 XL/XR 500. the stock 350X sleeve has to be removed and then the cylinder has to be bored for the 500 sleeve. you will also need a new gasket. i make my own so i'm not sure if the 500 gasket will work or not

[3WheelsForever]

What do you make your gasket out of? When you used to do this conversion did you feel it was worth the time? Im planning on 12:1 compression for it but have considered 10.25:1. Which would you go with? Im also planning on using a full out race cam, race port and polish, lightened flywheel, and a timing andvance key. And obviously the other stuff such as a bigger carb, aftermarket exhaust and open air filter. I thouht about having the cylinder nikasiled to keep the engine cooler. What usually go's wrong with these 350x engines after theyve been modified? Do they overheat to much? O yah this engine will be going in a quad that Im building so I can race next year.

[Black Sheep]

YOUR PUTTING THIS IN A QUAD:shocked: :doh: :nono: :fire: :bash: :thmbsdwn:

i'm half inclined not to help you now:rolleyes: ;) :chuckle:


let me correct you first..."When you used to do this conversion"...

i still do them and am working on one currently.

is it worth the time...yes and no. since i have 4 350X motors for me yes it is. since its not my only one i don't have to worry about reliability because i don't always use the big bores.

if i had only one motor i probably would not do it.

as far as potential problems...the worst thing to happen is a snapped rod wich can destroy the cases. you have to be carefull not to overrev them. i would not recomend lightening the flywheel. i'm also not a big fan of 12:1 compression although i have used them before. personally i prefure 10:1. as far as having the cylinder nikasiled. if you have this done you will need to get differant Rings since rings for a steel sleeve won't work. i'm not sure were you would get these. to help with over heating i recomend two things. 1 strip the black paint off it holds in the heat and does not cool as quickly (cool air has to travel through the paint first) 2. run duel oil coolers. finally change your oil after every ride and use only a high quality motorcycle/atv oil like bel-ray exl

[3WheelsForever]

Thanks Mr. ATC. Sorry about putting the engine in a quad lmao. Im just building a 350x/300ex conversion so I can race soon. Just wondering why dont you like 12:1? Because you dont want to run race gas or dont like the reliability? Ill probably end up going with 10:1 like you suggested.

[HondaATC500X]

Doesn't the case also have to be modified for the larger diameter sleeve?

[3WheelsForever]

Yes it does, I said that in my first post where I asked MR. ATC what else has to be done other than machining the cases.

[HondaATC500X]

Hehehe ooops :p