CRF's Only Forums

First off, we need to thank Ron Hamp (RHC) for really caring about the online community, and dedicating his time to making our sport faster and more enjoyable. That sense of helping one another out for free seems to get lost at the top level of the sport. But, folks like RHC and Kelstr understand the 'family' of motocross, and contribute here without monetary reward. I thank them deeply for what they offer our 'family'.

I read RHC's post about grinding down the backside of the decompression arm's lobe, to effectively reduce the amount of time that the exhaust valves are open during the kicking cycle. His theory, is that the stock decompression arm (weight assembly) gives too much duration of open exhaust valves, during kicking, making starting more difficult, especially with the 2008 model's cam, and especially if running the exhaust valves a bit tighter than spec (as most of those "in the know" do). However, this mod applies to ALL model year CRF250's. It seemed logical to me, and everyone who has been around this forum for a while, KNOWS that RHC is one of the most, if not THE most, knowledgeable engine builder/tuner in this country. I had a free night to spend in the garage, so I went for it, and took pics along the way.

What I didn't realize, is that the mod can be done WITHOUT REMOVING THE CAM! Great!

First, remove the seat and fuel tank:



Remove the plug wire, breather tube, valve cover bolts, and valve cover:





Its a good idea to check your valve clearances while performing this mod, so get to TDC by aligning the camshaft marks and crank marks (mine was a bit off in the pic), after removing the crankcase inspection plug on the right side of the bike (the cam lobes should be up and back from the valves:



My valves were: Both Intakes; .005", and both Exhausts; .009" (running exhausts on the tighter spec as builders recommend).

Roll the kick starter around to look at the decomp nub that you will be grinding off. When looking at the cam from the left side of the bike, the cam rotates the same direction as the rear wheel; counter clockwise. So, envision the area you will be grinding off...the backside. Or, wipe the decomp nub with some mineral spirits and make a mark on the backside of the nub, with a Sharpie pen, so you know where to grind:




Turn over the motor until the 8mm decomp retaining bolt on the right side of the cam, is at the top, so you can get a socket or T-handle wrench on it:



Remove the 8mm decomp retaining bolt (I did so with a T-handle wrench), and you may want to place a magnet parts catcher near the small setting plate, if you think it may fall into the head. If you are careful, the plate will stay on the bolt, and you can remove them at the same time:



Now, gently turn the motor over by the kick starter, one revolution of the crank (1/2 revolution of cam), making sure the decomp assembly stays in place with a finger holding it inward (you don't want it backing out, and catching on the edge of the head), until the hole that the decomp rod resides in is at the top:




Next, remove the decomp rod and spring, by pulling it straight out to the right, noting that the spring leg is wound under (clockwise) under the rod, and rests on the backside of the cam flat (this orientation will be important during reassembly):



End of PART 1, due to picture limits......

These are the parts that you have removed; the retaining bolt, setting plate, decomp rod, and spring:



Remove the spring from the rod, noting how it "hooks" over the end of the rod. Look at the end of the decomp "nub". You can see that it is sort of "V" shaped, and you need to remove all of the backside of the nub, saving the first .080" of lobe. Make sure you note the orientation of the nub, in relation to the roller, so that you grind off the correct side of the nub (the BACK, not the front). This is where the sharpie and observing the wear marks on the nub, come in handy:




This is where a caliper or micrometer comes in handy. I happen to reload ammunition, so I had one handy. If you don't have one, this mod is at your own risk, but I can tell you how to figure it pretty close; look at the top of the nub... you can see the worn contact area of the nub, where the roller contacted the nub. You want to remove the back half plus a bit, of where that contact wear is, and make it flat to where the nub's lobe stops. I measured and made a mark where I wanted to grind:



Clamped a Dremel with a 1/2" sanding drum in the vice, and carefully ground the spot away:



The area from where the nub's lobe starts, to where you ground off, should be about .080". Everything behind that, grind down to the point where the lobe's finished radius stops:



After getting the desired .080" of nub lobe, I took a piece of 1200 grit wet/dry sand paper and knocked off any burrs or sharp edges. This is what the end of the rod looked like after grinding:



Clean off all residual metal shavings off of the rod, and lightly lube. Position the spring back onto the rod as shown, with the hook over the weight arm:



Turn over the motor until the camshaft's decomp slot is on the top:



Push in the decomp rod and spring into the channel in the cam, making sure the spring is wound under (clockwise), and rests on the cam's cutout area, on the backside of the camshaft:



Then, rotate the motor carefully, so that the cam rotates 180 degrees, by the kick starter, holding the decomp rod in with a finger, so that the retaining bolt hole is at the top.



Then, slide the setting plate onto the bolt with the indexing spike towards the cam, and after putting a dab of loctite on the threads, install the bolt into the cam, making sure the setting plate's spike enters the alignment hole in the cam. Torque the retaining bolt to proper specs (I don't have the inch pound figure, I'm sorry...I did it be feel):




Put the valve cover back on, making sure to align the plug channel seal, and attach the breather tube, and properly torque the cover bolts, and install the plug wire. Replace the fuel tank and seat. Start it up easily, and smile.

After this mod, my bike starts MUCH easier. Hot or Cold, it fires as easy as my old 450 did. Surprisingly, kicking (perceived compression) is no more difficult than it was before the modification. I think the slight decrease in decomp duration simply made the firing cycle stronger at startup RPM, making it start 500% easier. My '08 starting blues are OVER! We all owe it to Ron Hamp (RHC) for making this mod known to us. He spends his time making our bikes faster and more enjoyable, and not very often you get that for free. Thanks Ron! :ride:

The part you shaved off is the part that makes that dam clicking sound when a hotcam is installed. This mod will also fix that. Nice!






fixed srry

ok...you win the best first/second post contest! excellent work. i'm curious how many who read this have done this mod and how effective is it?

ken

Just to be clear, this is for CRF250's only correct?

124 wrote:Just to be clear, this is for CRF250's only correct?

It pertains mainly to the 2008 CRF 250R.
The cam profile is so aggressive that they have developed a reputation for hard starting.

It may be a help for other CRF 250's with aggressive cams though.

~ wrote:

124 wrote:Just to be clear, this is for CRF250's only correct?

It pertains mainly to the 2008 CRF 250R.
The cam profile is so aggressive that they have developed a reputation for hard starting.

It may be a help for other CRF 250's with aggressive cams though.

Copy that. Thanks.
And thank you to Jimbo for the post. Much appreciated.

Anyone tried the mod yet? How it work out for you?

-Jim

Nice job ! Doug

I am going to do this to my 08 250. My bike has been very hard to start since new. If you lay it over you can forget kicking it, it's push only. I just installed a Athena 280 kit and had the carb modified by Tokyo Mods. The bike runs awesome but is still just as hard to start. My 450 starts first kick almost every time. This is my goal for my 250.
Ron, if this works I will buy you a beer... awesome job on modification directions. I own a machine shop. I can relate to your mod procedures and concept. I though about removing the decomp devise all together.

I will let you all know the outcome of this mod.

OK, I just finished the mod. Very easy to do. Took about 35mins from start to finish. I used a Dremel with the part held in a vice. Be careful, if you scrap the part it cost about 80.00 bucks from Honda and they don't stock the part. However you would have to be a complete moron to botch the job.
The bike starts easier for sure. It still makes the clicking sound though. I will have a better feel for it after this weekend. I will keep you posted.

PS
Tokyo Mods, carb mod is awesome! Best money spent on this bike for sure. The bike is completely different, NOOO bogg, super snappy with loads of power everywhere. Feels awesome!!!! Tokyo Mods did the mod in only one day too. Can't wait to ride the track.

Would anyone care to help me with this? I live in AZ..... Please? I have a 2008 crf250r and would love to get it started, only about 5 hours on it.

Be sure you time the motor off the flywheel timing marks, not the punch marks for the countershaft gear.

Jimbo,
I have an 07 250R that my kid raced last summer. It is completely stock but goes like crazy. One race the bike locked up solid. I got it freed up but took it apart so I could find out why. I found that the cam lobes were damaged with scraps and gouges as well as my lifter caps. The lobes were also flattened in some areas like it was dropped on the floor. I was running 110 Torko fuel too but I don't think that would have had anything to do with it. Have you ever heard of this? I want to put a new cam and and lifters in and I have heard to put in a stock 08 cam. It seems to work better than the hot cams they say. Is there any truth to this before I go and spent the money?
Looking forward to hearing from you.
Corey

Mod done as I can't race tomorrow so i'll try it on the local waste land and report back.