do big bores overheat?

[yzsurfer]

My tired '00 426 just blew 3rd gear. I'm tearing the engine down to fix this and will be doing the top end while I'm at it. I'm leaning towards the Eric Gorr 440 with hot cams and mild head work.

Has anyone had (or heard of) over heating issues with the big bore kits? I can't find anything in the past threads.

Thanks,

Jeff

[Supafreak_711]

I dont have any experience with yamaha's, but my riding buddy has a CRF470R which doesnt have any noticable overheating problems. At the GMB V race we waited at the bottom of a jump for the 393 bike to pass (Motoman393's bike) and we were both sitting next to eachother with our bikes running for a minute or so after the bikes were hot from running a 6 lap race (long laps). I'm not sure what coolant he is running, but I know that mine would have boiled over if I didnt have engine ice in there. I my 450 has boiled over several times in the past (mostly durring slow woods riding) before adding engine ice, so I am comfortable with saying that it works pretty well.

Hope this helps

[YZ250F_Rider]

It depends on whether the overbore uses a high compression piston or not. Some of the bigger overbores use a low compression one and heat isnt an issue. some use high compression ones and heat can be an issue if the cooling sytem isnt in good shape.

[642MX]

A big bore 426/440 shouldn't get any hotter than a stock 426. They all boil over if you don't get air thru the radiators.

[yzsurfer]

Thanks guys,

I hadn't heard anything about temps being a problem but the thought crossed my mind yesterday so I thought I'd post.

Anybody know if rejetting is required?

Thanks,

Jeff

[YZ250F_Rider]

always rejet when modding. From what I can gather the jetting tends to go a bit leaner with the overbore.

[Ga426owner]

My 470 has been ok with stock radiators so far...but fluiddyne and PWR make nice larger ones..do it do it do it big bore......

[odlaw19]

426 have pretty big radiators.

As said, check jetting.

[Chazlom]

I ran a 470yfz with head work , hot cams and a 13.5:1 piston without any problem ever for over three years. I have run my bike hard from Glamis to the High Desert races and overheating was never an issue.

It was a great bike, check "my garage".

[Ga426owner]

I ran a 470yfz with head work , hot cams and a 13.5:1 piston without any problem ever for over three years. I have run my bike hard from Glamis to the High Desert races and overheating was never an issue.

It was a great bike, check "my garage".

past tense....Chaz? Did you sell that beast?

[Chazlom]

Yep.......three weeks, 10 hours and 26,1/2 minutes ago!? :p

Just got back from Glamis with my new bike all tricked out. Just got the 06 Husky 450, frame powdercoated, Suspension work on by the best......and still....I wish I had the 03 YZF back.....Damn

To the Kid that bought my bike, You'll never know what went into that bike....damn your lucky!

http://www.gpkings.com/

Chaz

[Ga426owner]

Yep.......three weeks, 10 hours and 26,1/2 minutes ago!? :p

Just got back from Glamis with my new bike all tricked out. Just got the 06 Husky 450, frame powdercoated, Suspension work on by the best......and still....I wish I had the 03 YZF back.....Damn

To the Kid that bought my bike, You'll never know what went into that bike....damn your lucky!

http://www.gpkings.com/

Chaz

sounds like you regret selling it...I know what goes into it Chaz.....lots and lots of money.....same with mine.