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Discussion Starter · #1 ·
Hello all, new member and first post. I have gone through ever post I could find when rebuilding the quad and have tried everything I can think of. I am having an issue after the rebuild and was hoping someone could help. I have set the timing four times at this point and still have a no start and recently had two backfires that knocked the carburetor off the intake manifold. My issue is every time I align the lines on the cam sprocket to the block I have a good amount of play in the cam (like an sixteenth of a turn) it was the same on the old cam and new cam (niche performance cam). The reason I did the rebuild was to get rid of the cam chain knock noise with a Part # 14401-MEB-671 cam chain for a CRF 450r. I read in multiple posts that it was the best cam chain to use for this application. Could this be the issue? I also replaced the tensioner with a manual tensioner. The decompression pin was not used when I took the engine apart and I didn’t put one in as I used an aftermarket cam. I set the valve lash and replaced the coil and cdi. The fuel might be degraded but I tried staring it with staring fluid and it didn’t start. Any advice would be appreciated, thanks.
 

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While you have been misled about the CRF chain being "better", it is wider, lighter and cheaper than the TRX chain - it is this way because the CRF is for racing and the chain is expected to be replaced frequently as part of routine maintenance - the CRF chain is the same length, but it will wear the guide side rails off in a short time and it will walk from side to side on the cam and crank sprockets.

The only thing BETTER about the CRF chain is it is CHEAPER. The TRX is designed for recreation and low maintenance compared to the CRF which is lighter, revs higher and is rebuilt after every 30 hours of racing.

A manual tensioner is good for wearing out chains and guides unless you know and are practiced in adjusting cam chains.

The first thing you need to do is verify the piston is at TDC when the cam sprocket is installed. You can't adjust the 'timing' - the timing is triggered by the flywheel. I recommend you verify the T mark on the flywheel is aligned when the piston it at TDC. To do this, remove the spark plug and set the flywheel at the T mark - use a soda straw through the spark plug hole and feel the movement of the piston up and down - when the piston is at TDC, verify the T mark is visible.

Note: there is no 180 degrees out of time - the ignition fires every rotation of the crankshaft so it can be assembled at TDC of the compression stroke or the exhaust stroke and it will still run.

So onto the basics; how much compression does it have?
 

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Discussion Starter · #3 ·
Thanks for the reply. I should have a chance to test TDC tonight as well as hopefully loan a compression tester from autozone and check that out. I will let you know once I am able to check them both.
 

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Discussion Starter · #4 ·
So after a long week of an anniversary, the Marine Corps birthday and Veterans Day, I was finally able to check what you suggested today.
The piston is at its highest point and the “T” is in-line with the timing mark.
I checked the compression and am getting 0-10 psi. Any ideas?
 

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Discussion Starter · #5 ·
What would happen if the crank was turned backwards a bit when setting timing the first time? Would that mess with the decompression pin? Also it never had the decompression pin it, when I took it apart and I didn’t put one back in. If this caused an issue how can I fix it?
 

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If the new 'performance cam' is billed as high lift, then no decompressor mechanism is on the cam and the pin and spring are supposed to be removed anyway. Rolling the engine backwards has no effect on the engine other than causing the starter motor to spin. With compression that low, I would lock the crank at TDC and apply air pressure to the spark plug hole to see where the air is going, then proceed from there.
 

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Discussion Starter · #7 ·
So I was finally able to send some air into the plug hole. I left the engine at TDC when I tested it and I did get air coming out of the intake manifold. I still have the exhaust on and didn’t feel or here anything from the muffler. I did check my valves before and from what I remember I used the .010mm for intake and it was touching. I’m guessing when I first “set the timing” I messed it up and bent the valves. If that is the consensus, I will buy the tool and replace the valves. Any ideas for a good but cheap valve compression tool.
 
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