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mechanical cam chain tensioner 150problem?

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Anyone try one of these yet? http://www.tokyomods.com/tensioner.htm

I have some type of problem where after a while my intake valve starts hitting the top of the piston on my 150. I pull the head off and notice nothing broken. Last time I put in new valves in. Rode it about 15x then it happens again. This is the 3rd time. I think the tensioner might be bad.

I'm running a BBR175kit & cam w/dual springs.

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Unibrow,

I don't think you are experiencing a cam chain tensioner problem. I would bet that the problem is that you need to "Degree in" the cam shaft.

When your engine was being assembled with the new hi output parts, the re-assembly needs to be "dialed-in". It is up to the engine builder to make adjustments to the cam timing and valve relief pockets to insure proper running clearances.

Do you still have the cam card?? The cam should have been delivered with all of the cam timing data. Your intake valve hitting the piston indicates less than ideal clearance (obviously) and or improper valve timing. If the intake valve is hitting the piston, the cam/valve timing may be to advanced. The valves usually only come close enough to hitting the piston at the "overlap" position near TDC.

One of the problems with the camshaft design on these engines is that the cam sprocket hub (part with two threaded holes that holds the cam sprocket) is pressed on at the factory. Almost every stock cam's mount is in a slightly different location in relation to the cam. No two are ever exactly quite the same. They fall into the factory "spec". Most cam grinders have to remove this mount to grind the cam. After their work has been completed, they re-install the hub, using their best effort to reinstall it in the same position before they removed it. What if it was already off a bit??

Just a few degrees can make a huge difference in valve timing events.

Depending on what cam BBR used for the "core" and how the cam grinder "set up" your particular cam, the camshaft appears to be slightly out of time. Have you tried to alter the cam timing by one tooth on the cam sprocket?? The cam timing assembly instruction are clear enough.

The cam bolts need to be in a vertical position, and the two lines on the cam sprocket need to be in a horizontal alignment when the crankshaft is at TDC...... But are they?? Most of these engines never are. If your cam bolts appear to "lean" more in the 11 oclock (top bolt) and 5 oclock (bottom bolt) than your cam timing may indeed be too advanced This condition would allow the problem you are experiencing. Adjusting the cam timing by one tooth may cause the bolts to lean toward 1 oclock (top) and 7 oclock. (bottom)

It seems like a lot and may be too far in the opposite direction, but I would try it and see. If your cam bolts are already leaning toward 1 and 7, then the cam grind and or cam sprocket hub is probably a little off.

If you do attempt this adjustment, DO NOT TRY AND KICK IT OVER !!!! THE ENGINE SHOULD BE ABLE TO ROTATE FREELY BY HAND AFTER YOU HAVE CHANGED THE CAM TIMING. IF NOT, THAN A VALVE IS PROBABLY HITTING THE PISTON!!

Again, one tooth may be too much in the opposite direction, but it is worth a try. The only way to truly assemble it correctly is to "degree" it in.

This process is straight forward enough, but too lengthy to describe on this already long reply. PM me if you would like to hear more.

Mike

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Unibrow, Coeshow is right. I had a similar problem w/ my XR200. I bought a Roller cam for it and when I assembled it it appeared that the intake valve slightly hit the top of the piston. I advanced it 1 tooth and Viola no problems. wierd how it happened after it was warm though??? I noticed mine right away.

-Robbrt

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Thanks for the tip I'll try the 1 and 7 position and see what happens. If it happens again I'm going to swap out the cam and rocker arms. Know of any other good cams? It just seems strange it will run fine for a while then for no reason while riding it will lose power and start hitting.

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Unibrow,

I agree that it sounds wierd what is happening. It's hard to try and diagnose certain things like what you are experiencing sometimes without actually being able to "touch" and see the engine personally.

Good luck on your quest.

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The Tokyomods mechanical cam chain tensioner increases horsepower, extends cam chain and cam chain slider life in addition to eliminating any possibility of the automatic stock tensioner failing, causing catastrophic engine failure. It can be installed in minutes with no special tools needed.

How would it incease horsepower?

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Not familiar with the Tokyomods tensioner! :banghead:

A HP increase is possible with a properly tensioned cam chain. Too loose throws off cam timing and too tight increases friction.........wears out chain, bows, sprockets, bearings, etc. also! Many models have had tensioner problems over the years!🤣

Jumping a tooth to try and stop valve interference is NOT how you do it!!! 🤣 Degreeing the cam is fine, but only TIMES the cam to the specs. it was designed for! You can still have clearance problems! Didn't BBR have complete installation instructions for installing their parts?

You need to get a set of instructions like Powroll has sent with their bore kits and cams for years, and go through EVERY SINGLE STEP..........NO SHORT CUTS! :banghead: You won't believe how many problems you can prevent and how much money you can save! It's just part of what's necessary to build a good performance motor!🤣

Old School Al

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The stock cam chain tensioner on these engines is a very nice piece. A big improvement over the XR200 style, and fully automatic as well. Honda did a nice job on the design.

The Tokyo Mods replacement would make it very easy to OVERTENSION the timing chain. Again, the stock tensioner is fully automatic and is self adjusting!

I am not familiar with the bigger CRF's so I can't say if the stock tensioners on those bikes are troublesome or not.

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