Rebuild CRF450 Head

[mideastrider]

It’s time to rebuild the head on my crf450, I already have the parts, new valves, springs, retainers, seals etc. all OEM. Now I see a kibblewhite intake set for the Honda includes everything.Debating if I should use instead of the oem. It’s been talked about on here a lot and appears to be the way to go. I went to kibblewhite website just to read up on it. I am confused on whether to lap/seat or not. In the FAQ section it states the valves are designed to be faced. It all so says “All KPMI Black Diamond Stainless Steel Valves are impregnated by a special German process to .002" deep with a .0002" surface build-up to improve wear properties and reduce friction.” Seems like facing the valves would begin to remove this special process. My question is it ok to just change the intakes and keep the oem exhaust valves? I will have the seats cut/resurfaced will it be necessary lap the intakes?

 

[Rich Rohrich]

Seats properly machined with carbide cutters do not need to be lapped afterward. The key is having the seats machined by someone with the proper equipment and most of all skill.

The Kibblewhite stainless steel valve and race spring kit is the best bet in terms of reliability and cost per hour of riding.

The OEM exhaust valves are good but the Kibblewhite exhaust valves with their spring kit will far out last them.

 

[skos]

Seats properly machined with carbide cutters do not need to be lapped afterward. The key is having the seats machined by someone with the proper equipment and most of all skill.

The Kibblewhite stainless steel valve and race spring kit is the best bet in terms of reliability and cost per hour of riding.

The OEM exhaust valves are good but the Kibblewhite exhaust valves with their spring kit will far out last them.

I agree. +1

 

[whenfoxforks-ruled]

In all the GOOD stuff I have read, none get lapped, on mx bikes. Except for the really steered wrong. The issue seems to still be, some guys are not re-cutting the seats when on the rebuild. Vintage Bob

 

[Ol'89r]

Seats properly machined with carbide cutters do not need to be lapped afterward. The key is having the seats machined by someone with the proper equipment and most of all skill.
.

While I totally agree with that statement, I always go to the extra trouble of lapping the valves in with Dykem. Also known as Prussian blue or machinists dye. It is not an abrasive cutting/lapping compound, only a dye. It does not remove any material from the valve or seat it only shows you where the valve is contacting the seat. Or where it isn't. If there is a slight chatter in the cutter or an uneven seat it will show it before you go to the trouble of putting the head back together.

If it were mine, I would replace both the intake and exhaust. The stock valves can break over time but the SS valves won't. For the extra expense, you would have a head that would last for a long time.

Also, after you assemble the head, pour gasoline into the intake and exhaust ports. If a valve is not sealing properly, the gas will leak through the valve and show it instantly.

Just my $ .02

 

[whenfoxforks-ruled]

That 2 cents on the dye is priceless!

 

[mideastrider]

I finally got the rebuild finished about 4 weeks ago. I had already purchased oem parts for the head earlier in the year so I decided to use them up. Freshen up the bottom end with new oem crankshaft and bearings. I cut the seats installed the new valves,(no lapping) did the gas test and checked out good. Rechecked the valve clearance after the first race (2 hour) and its looking good. Its got 3 races on it now and running great so far.