2002 CRF450R rebuild questions

So I picked up this pile of a bike for a couple hundred bucks and I'm starting to get through rebuilding the engine. Looking for some help on anything I should look out for on the 02 model specifically. 

Goal is to do full engine rebuild and have a fun/reliable backup to my 06 crf450r. I only ride trails and dunes, no track. 

Some quick questions, I've heard many people are scared of the auto cam tensioner (especially the early crf tensioners). I do NOT want a manual one, are there any options for a better auto tensioner? (as in a newer crf tensioner that would fit) 

Piston options, would prefer oem. Can I fit/should I fit a piston from a newer crf? What years work and with it fit properly with an oem 02 head with stainless kibble white valves? 

Planning on having the head done by fast heads with stainless valves and already have a brand new oem crank and a clean oem cylinder. Also have an 03 or 04 airbox already and a full yoshi exhaust. Any other hints or issues that I should fix that are specific to an 02 I'd appreciate! I'm plenty mechanically inclined just lacking in knowledge of this particular bike. 


If not manual, you're only option on a cam chain tensioner is OEM but use an '03.

'02 to '08 pistons fit your bike.  I wanta' say in '04 the piston went to 12.1:1.

The '02 airbox is junk with it's flush mount boot and screws that went into the airbox and made it difficult to get a good filter seal.  They fixed it in '03.  They went back to a double lip boot and a steel filter base.  Good stuff.  If that mounts up, that is the box to use. If not, drill out the nubs (I'll get you the bit size) and use the boot, etc, from the '03 airbox.  Seal it up and you're good.

That bike had understeer problems, we found that a good sand tire up front helped.

Edited by HRC27

Here's some pics that you might find helpful if you have to mod the '02 box.  Pics are of a CR250R airbox that I modded for a 500AF.  Honda never corrected the CR250R airbox from '02 to '07.  Maybe not all will apply but perhaps they'll help.

The drill bit size is shown.  11/32".

Hopefully, the '03 airbox is a direct fit for you. :thumbsup:






Thanks for the reply! I already have the 03 box and it fits well, I resealed  the boot to the box on it too just in case. 

Why dont you want to run the manual tensioner? You'll pay less attention to it than you will any other part of the bike, I can guarantee you that. The Auto tensioners were junk, no matter what year they are.

I'd put a crank in it, replace the main bearings with OEM parts if your going to keep it. Cam chain too. And just get an 05 air boot. It had more volume. And piston wise, I'd put a 13.5:1 Wiseco in it. They can be had cheap. They're every bit as good as an OEM and the 02 cam LOVES a little more compression. The 02 also had some really funky jetting in it from the factory. The main jet was way bigger than it needed to be. I think they came with a 185, it only needs a 180 max at sea level. If you go to the 13.5:1 piston, it may want a 45 pilot, but if it's all sealed up well and the head is in good shape, the 42 usually works fine. 

I really don't like manual chain tensioners and at least on my 06 crf450r and my 05 trx450r I've had zero issues with the auto tensioners. Maybe it's because I don't ride hard that I haven't had issues? The bike isn't constantly hitting the limiter then dropping to idle when I'm out. The bike came with a low hour oem tensioner and a manual one, maybe I will just use the manual one that I've got. 

I am a fan of wiseco, are these bikes happy on pump at 13.5:1? Also, just realized while doing some teardown today that it has a stage 1 hotcam in it. I have a feeling I'd prefer the stock 02 cam but the goal is to keep the rebuild simple and use as much of what I've got as possible. 

I will be doing new oem bearings for the crank, very cheap insurance. 

That 13.5:1 piston and Stage 1 hot cam dont play nicely together. If you dont mind kicking like a damn fool to get it started, it pulls pretty hard down low, but Id never recommend it.

The stock post 04 piston is 12:1, which works fine with the stage 1. The OEM 02 Honda cam is very similar to the stage 2 Hotcam, which is why it really comes to life with the 13.5:1 piston.

The other thing you may want to think about is the entire crank, because the rods dont last forever. @280 bucks, it's pretty cheap insurance.

I've got an entire bucket of failed OEM cam chain tensioners. One only had about 4 hours on it. It's up to you, but I dont allow anything with my name it go out of my shop with the OEM tensioner in it. If the customer insists...I pull it after I start the bike for him and hand it to him. Let him stick that shot gun in his own mouth.

But, with a stage 2, or the stock cam, even with the stage1 and the 13.5:1 pump gas is fine because the head has a really good combustion chamber to start with. Another relatively cheap, very effective hop up tip is a later model ignition box. 05-06 were much more aggressive. You can probably get the 05 harness and box cheap on ebay. Adapting the crank and stator connection is a no brainer. The wire colors are the same. The connections are different but not terribly.

I do have a brand new oem crank so we're good there :)

I actually think I have a full spare ignition from my 06 crf but don't whether it works or not. 

Guess it's time now to order crank bearings and gaskets, try to get the bottom end cleaned and buttoned up. Then I'll forge ahead with a piston and shipping out the head for a rebuild. 

Throwing on a fresh pic of the bike since it got some new white side panels. Would have replaced them all but this is supposed to be a relatively cheap bike. Coming up soon should be engine teardown 


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