polaris predator cam timing

JoeW · #1 (**permalink**) 10-28-2011, 08:22 PM

I was putting the rebuilt head back on my garage sale special tonight. When I went to line up the cam gear timing marks, someting was not right. With the crank mark on TDC and the piston at the top of travel, the lobes on the cams were pointing down! I looked several times at the manual and rechecked the marks on the gears and it just was not right. I know enough about cam timing, with the piston on TDC the cam lobes should be "rabbit ears" intake valve having just closed and the exhaust valves on their way to opening. The only thing that could have happened is the cam gears clocking on the shafts. Has anyone ever heard of this happening? FYI, all 4 valves were bent when I bought the machine.

JoeW · #2 (**permalink**) 11-15-2011, 07:02 PM

Well, I didn't get a response on this but, I bought a set of used cams on Ebay and everything lines up right on the engine. Compairing the old cams to the replacments, the lobes are at least 120 degrees off. I pressed the gear off of the old intake cam and found no galling from the gear spinning on the shaft. It took a bit of pressure to get it apart too. I don't see how thay could have moved. It's a mistery.

shui5612 · #3 (**permalink**) 11-16-2011, 10:15 AM

there's your answer. if you ever rebuild an engine, change out parts that could have been damaged by other parts.........

but i usually leave it to the pro's to do my things, if it doesnt work, then i guess theyd be buying me a new quad.......

joshr08 · #4 (**permalink**) 11-16-2011, 04:08 PM

its actually more common then most think on this motor. There is nothing on these cams to keep the gear in place other then being pressed on and they do from time to time most. Good thinking on getting a used set just keep a close eye when your putting it back together like you have already done to make sure the used set is good. even 1 tooth on the timing on this fuji motor is put a valve right into your piston.

JoeW · #5 (**permalink**) 11-30-2011, 04:26 PM

Well, I finally got the time and my 17 year old to the shop on Saturday. I wanted him to finish assemling it, under my supervision, I cleaned the carb and drop the new/used gas tank on with fresh premium, and it fired right up! Adjusted the idle and off we went, Runs great! Yesterday JP, my son went to start it and the starter just spins. The drive gear or sprag clutch must be out. Oh well, back to the shop for repair. When you by a quad at a garage sale for 250 bucks youhave to expect a few problems!!!

JoeW · #6 (**permalink**) 01-22-2012, 10:28 AM

OK, after purchasing 2 used starter clutches, I have made a decent one. I reassembled the starter drive and flywheel and no start. It seemed to have compression pushing out the intake. I popped the valve cover and the intake cam is out of time. I backed off the chain tensioner and resset the cam timing and it fired right up! A little lap around the parking lot and it runs great. A couple more laps and the engine stalls, on restart it idles fine but no power and won't rev. I think the cam timing jumped again. Any ideas?

joshr08 · #7 (**permalink**) 01-23-2012, 02:34 PM

have you checked you cam chain to see if its in spec and also your cam chain tensioner

JoeW · #8 (**permalink**) 05-24-2012, 07:54 PM

It's been a while sinceIi posted this but, I wanted to get this out to those of you that may be having the same problem. Here's a quick outline...

1. Bought a non running 04 Predator 500 at a garage sale
2. Discovered the cam timing to be off and all 4 valves bent.
3. Replaced valves.
4. Upon reaasembly, found the cam timing marks on the gears to be off, by quite a bit.
5. Purchase 2 used cams on Ebay and timing marks lined up properly
6. Bike ran for one day and the starter drive fails.
7. Purchsed 2 used starter clutch assemblies on Ebay made one good one.
8. Bike ran for about 20 minuts and the cams jumped time again. (no valve piston contact)
9. Chain measured to be in spec, tensioner appears to be in good working order.
10. Ordered a chain tensioner from loacal dealer, I didn't want to take a chance with a used one.
11. Chain tensioner on back order.
12. Wait
13. Wait some more...
14. New tensioner arrives finally!
15. Set cams to proper alignment, and install new tensioner.
16. Bike runs great! it's been a couple of weeks and a half dozen outings and no problem.

Three dealers told me that these bikes do not jump time and no one believes that the timing marks on the gears were wrong but, this is what I found. Just wanted to share my experience.