[SIZE="4"]Hey guys i am new to this forum and im having issues with my pred. I bought it off a guy a few months back as a quad that needed alil work to get running which wasnt a problem for me, but i cant seem to get it running again. The guy i bought it off of ran the thing till the timing chain stretched so far and the engine bent the intake valves and spun the gear on the camshafts. Obviously it wasnt running at all. So that being said i bought stock valves from the stealership and i took the head to my mechanic to put the new valves in. He lapped the valves and put the valve lash into spec on all four valves. He told me that the exhaust valves were still good too. I took the spun camshafts and found the specs online and tack welded them into place, they are damn near close to factory specs. I reassembled the engine completely and the right way, i do a lot of my own work and have a lot of experience. Anyway, when i go to start it up, it just cranks and cranks with an occasional backfire thru the carb. It has a new spark plug, its gapped at .035in and it has a blue spark. It has fresh fuel, clean carb, and the timing was on the spot unless my cams are just that off. It also has a compression of 100psi but im using a cheap guage with a long hose so it probably has more than that. I am completely stumped with this quad. Does anybody have any idea whats going on with it?!?!?!?!?!

 

You have spark,fuel and 100 psi on compression which is about right with the compression release device on the exhaust cam.If the cam chain is timed up to the cam sprockets and crank sprocket correctly but won't crank,just backfires,I'd be suspect of what degree the sprockets were welded to the cams. Close to factory specs may not be good enough? Just a thought.

 

I agree i dont think the camshafts are close enough, but is there any other possibility i should look for? Im only asking because i dont want to make a 300dollar mistake on new cams for the quad.

 

Also, is it important to have the timing chain gold links marked up with the cam sprockets and crank sprocket? I didnt really pay attention to that as any other quad i have worked on didnt have any specific marks like that and it honestly didnt seem like it would make a difference. Is there a reason the gold links have to be lined up correctly?

 

No I wouldn't want to guess and throw parts at it either.The colored links are just a handy way for some to line up the sprockets and once turn the engine over they don't line up again. Doesn't matter on the links.Before I guessed at parts,I'd go through all electrical checks as this could be the problem on not starting,backfiring and not a mechanical problem. Just go through the electrical tests in your manual.If you don't have one,you can get one here for 5 bucks.Polaris ATV Service Manuals PDF Download

 

Hey guys im back with still the same issue! So i finally had time and money to work on the pred and still nothing. I have brand new webcam camshafts installed and i bypassed the fuel pump. As i said before i have new valves. I have done a leak down test and it seems im losing air out the exhaust but it seals up when i start to turn the motor over. When at top dead center and i apply pressure it has no leaks at all when testing at 15psi. However i did a compression test and came up with barely 35psi! What could be causing this suddenly? Timing off? It cant be the piston rings can it? There was no air passing the piston rings going into the case or i would have heard it and smoke would have revealed the leak. I have fuel and spark so im clueless! I really need some help.

 

Somethings wrong with 35psi.. Yes if cam timing is off enough to barely have the valves cracked open or valves shimmed too tight that can cause compression loss.Think I'd retrace my steps on timing first,then make sure valve clearance is within specs. A leak down test with at least 90psi of air you should be able to tell if there's any leaking through the valves by the gauge itself and by listening to the back of the muffler and back of the carb for any hissing,plus past the piston rings by any air coming from the crank case vent tube.

 

No air is coming from the crank vent tube at all. Nothing from the intake, intake valve lash specs are the following- left side is .006in right side is .005in. When the piston is all the the way down the exhaust leaks fairly well. Exhaust valve lash specs are both .007in. Web cams suggest all valves to be .006in but my professional mechanic said i could get away with such small differences. So i assume timing is incorrect. Is there a difference for which stroke i time the bike on? My timing seems to be correct according to the pred manual.

 

You're getting "strokes" confused with just having the piston at tdc. It's at tdc that you install the cams with the marks parallel to the head. Just look over the cam timing again in the manual. If it's got compression,spark,fuel and air,and timing is correct it should run. If you're sure the piston is at tdc,you can use the plated links if it helps. Just wiggle the chain around,line up th eintake marks parallel with the head,then use the second plated link as shown.

 

According to the manual my quad is perfectly timed, I have redone the timing on this this so many times im almost wanting to guess that webcams has their timings different than what the manual says. I will call webcam and ask just to rule that out. I still ha and found any leaks in my quad anywhere but the exhaust when the piston is at the bottom. Everything is well sealed when the piston is at tdc with 15psi leak test(anything higher is too hard to hold at tdc without piston moving). I honestly dont think im doing anything wrong here, ive completely rebuilt blasters, warriors, 400exs, yfz450s and a ktm 250sx and I just cant find the problem! Piston rings are fine, I had over 100psi before these camshafts and nothing else has changed so timing must be the issue. I will take pics of my timing and post them at 5pm today.