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08 CRF450F Basket Case - what to replace?

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OK... I did what you never should do, I bought a project bike off craigslist for $750. Bike shop had pulled the top end off and declared the crank was "broken". Kid claims that it started backfiring then stopped completely.

Unknown hours but this kid didn't maintain it. Gearbox oil wasnt bad but the crank oil and filter were full of metal grit. Valves look original and dont seem too tight. Exh rockers measure .011 inch. Cylinder still has xhatching but there's piston scuffing on the front/rear walls at the skirt. Piston has transfered some metal. Cylinder looks like it might be ok with a hone job. Big end crank bearing looks like toast to me but I haven't split the cases yet.

I'm planning to use this as my cheap re entry into Vet Novice MX at the local tracks. Since the stroker and big bore kits are not much more expensive than stock parts, I'm tempted to build a 511cc fire breather but then my common sense comes back.

Right now Im leaning toward just a stock 450cc rebuild with a hot rods crank and a 13.5 wiseco piston. New manual cam chain tensioner and chain. Hone the stock cylinder. Clean up the head and do some minor porting. Looks like the stock titanium valves are stiil there so I will probably just lap them and reuse. Have considered the Stainless valve options but not crazy about adding all that mass to the valvetrain. Should I do new valve springs even if I keep the Ti valves?

Probably keeping the stock cam because the torque curves I've seen for stage 1 and 2 cams look like they just rock the curve about the mid rpm point. I don't want either a low end or a high end curve.

If there's any good reason to do the 3mm stroker crank now would be a good time to tell me...

Will go thru the carb too. Old guys like carbs.

As you can probably tell this isn't my first rodeo with dirt bikes but my last thumper was an 85 XR600 that I bounced off every tree in Michigan. I'm guessing that this CRF might be just a bit different... In a good way...

Will it have more torque than my old '79 KX125? :)

All input appreciated. Shop manual is in the mail. Feels really good to wrench on bikes again. Would be nice not to kill myself the first time I ride it.

Thanks

Jim

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dont lap the ti valves they ill not last just get new ones if you wanna stay with ti there like 30$ each at hondaeasttoledo.com also replace the cam chain only like 35$ its worth it trust me i went to stainless on my 05 and they lasted forever till i sold it. But do not lap your valves

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you can get a hotrods bottom end kit which has everything you need for rebuilding the bottom end, stock or stroker. if you go with the stroker plan on using the stock piston and it won't make more hp just torque. i'm still searching for 60+ hp but as of now it makes almost 39 ft.lbs. torque. 

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450cc of AMA-Legal braaap:

IMG_00000294_zps695cddbf.png

Edited by Eddie8v

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38.87 @ 6619, 56.4 @ 8816. This dyno is a bit conservative with numbers. The bike has won 4 races in the Steve Nace Allstar Series, 3 shorttracks and 1 halfmile. Power curve is very flat.

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Thumper Racing sells BB kits for that bike.  i would recomend bumping it up since you are in there anyways.  the BB kits make the bike easer to ride. 

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No issues with overheating or being slow to rev with the stroker or big bore kits? Vibration issues since the counterbalancer isnt designed for that bore & stroke?

Do I need to have the valve seats recut if I go with stainless valves?

Thinking that I will need to do a stage 2 or 3 cam if I go for the full 511cc kit. And a nice blond massage therapist. ?..

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I would start with the blond, pleasure before work...

The BB kits seem to run cooler than stock from what i read. In my experiences i have not overheated any BB bike i have owned. The vibrations are no more than stock, and sometimes less than stock depending on the bike. They do seem to rev a little slower, but nothing that noticeable since the bike is pulling harder than stock. In a stock bike you rev it to get the pull, but with a BB bike you don’t have to rev it so much. The motor also lasts longer than stock because you are not into the rpms so much.

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I haven't pulled the valves out and inspected them (and the seats... and the guides) yet - but I did find some posts that say DO NOT install new SS valves without cutting a face on the seats.

 

So - my question is, after buying new valves, new guides, paying for guide installation and seat cutting - how much do you have invested vs a new or rebuilt head with the SS valves/springs/etc already on it? What's be best source for machine work/a new head? (as I type there's a big bore thumpers banner ad playing above this post.... :)

 

And do people usually replace the exhausts valves/rework the seats?  - or are they OK since they are already SS?

 

Now leaning back toward a stroke/big bore rebuild... but I'm not James Stewart looking to clear every triple at the Daytona Supercross, but I would like the rebuild to last...

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