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I'm looking into doing the cam mod on my klx250sf and had a couple clarification questions. Forgive me if these have been asked before, but all the threads I could find referenced pictures that were no longer existent. First of all, as far as the position to start from, as long as I set the intake and exhaust dashes on the gear even with the head am I good? Or do I have to find TDC at a certain stroke(don't see why this would matter, but figured it was worth asking). Secondly I want to verify the direction of rotation of the gears relative to the chain. I'm attaching a picture and my understanding is that I rotate each gear in the direction drawn 2 teeth, is this correct? Secondly are there any good sources for rejetting suggestions with this mod? Also I'll be performing this mod on a totally stock klx, what mods should accompany this? (wondering about airbox mainly, but eventually I can do the exhaust when I have money too)
Put each cam onto the "new" gear holes, rotate intake cam-and-gear two teeth to the left (counterclockwise), Rotate the exhaust cam-and-ger two teeth to the right (clockwise).. Done..
Yank the spring off of the KACR,, Done..
No need to add any additional mods or setup.. Power increase on a dead stock bike is quite noticeable..
I inscribed a line even with the head in the ends of my cams to serve as a sanity check when it was done. TDC compression is the reference point for the work because it is easy to get to and a good baseline crank/cam position with both cams on their base circles. Pictures show how mine looked after doing the MCM. Intake slightly advanced and exhaust slightly retarded as expected. With stock exhaust I would think a very modest increase in main jet size would be sufficient. I would have no idea really because my bike had an aftermarket silencer from the beginning.
I inscribed a line even with the head in the ends of my cams to serve as a sanity check when it was done. TDC compression is the reference point for the work because it is easy to get to and a good baseline crank/cam position with both cams on their base circles. Pictures show how mine looked after doing the MCM. Intake slightly advanced and exhaust slightly retarded as expected. With stock exhaust I would think a very modest increase in main jet size would be sufficient. I would have no idea really because my bike had an aftermarket silencer from the beginning.
well crap. I just did the mod but I did it at the TDC where the cams are pointing in towards each other. I still don't see how that would matter, but the bike wont start now that it's all buttoned up. All I did was take the cams out completely, rotate the sprockets to EX on intake and IN on exhaust and then put them back in. I put them in pretty much exactly how you show with intake about two teeth CCW from the line being on the head and the exhaust about 2 teeth CW from the line being on the head.
Ok, I took a second look and I just did it wrong. Basically I was going off the wrong lines and each cam was 6 teeth too far away from each other. I put them in the correct spot and the bike fires right up, but there is a very loud sort of tapping noise that doesn't seem like a good thing to me. When I measured my valve clearances all are between .15 and .203 mm except one exhaust valve is between .203 and .254mm
Last edited by Clay Matheson; 10-14-2017 at 01:17 AM.
If you get your cams out of time with the crank enough, it probably is possible that a valve could hit the piston.
I don't know of any way to determine if the crank is on the TDC of spark or TDC of exhaust/intake.
Forum Question: Will the plug fire if your just turning the engine over with a wrench?
If you get your cams out of time with the crank enough, it probably is possible that a valve could hit the piston.
I don't know of any way to determine if the crank is on the TDC of spark or TDC of exhaust/intake.
Forum Question: Will the plug fire if your just turning the engine over with a wrench?
Ya I'm just praying that didn't happen. The fact that it still starts up fine now seems to hint that it didn't, but hard to know for sure without inspection. I'm hoping at this point I just have an issue with the kacr or cam chain tensioner. I don't know what else would cause that sound.
It is not the KACR.. For one thing, there has never been a reported ticking/noise issue with the KACR, Its' design is such that it is mechanically stable once idle speed (and up) is achieved. You likely have the typical tensioner noise.. I certainly did once I got mine back together, had to loosen the tensioner quite a bit for the noise to abate - which was counter intuitive, but worked..
Congrats on screwing up the MCM - and then fixing it - without destroying your engine..
10-13-2017, 02:22 AM
Cam mod clarification
