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Bf8: Flywheel get stuck occasionally during compression stage???

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USMC916

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Hi, I just got this motor (8hp 4 stroke) and now it won't start and the flywheel would get stuck occasionally during the compression stage. I took of the the pull start and turn the flywheel pass the sticky point with a large screw driver. It would turn and get stuck at the next compression stage. It seems like I could turn it easily about 17 times and then it would get stuck 6 times, the pattern repeats. I took the plugs off and check to valves and their fine not sticking, cylinder walls are perfect no scrapes or carbon deposits. What could be wrong? Please help? And how to do you remove the flywheel? I took all the bolts off and it wont come off..
 
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To be honest I'm not an expert on this model but I can tell you that all the flywheels I've removed were held on by the large nut in the center. You need a tool to pull it off. A harmonic balancer puller sometimes works if you have bolt holes to attatch it but usually a 2 or 3 jaw gear puller is ideal. Back off the center nut untill its even with the top of the crank and put the puller on pretty tight. If it still doesn't pop loose hit the large bolt in the middle of the pulller with a hammer several times and tighten it some more. Repeat this process until the shock of the hammer blow pops the flywheel loose. Spraying penetrating oil into the center of the flywheel may help but often if it is that stuck you might just leave the puller on it and check it every day tapping the puller bollt and retightening as necessary. Don't hit it too hard or you could drive the puller bolt into the dimple on top of the crankshaft causing the end of the crank to swell and the nut might nut come off. That's one good reason to leave the nut on and aroound the top of the crank while you're using the puller. The other reason is so the flywheel dose'nt jump off and fall on the floor when it comes loose, possibly damaging the magnets inside. Do not hit the flywheel itself. If you have to beat the puller excessively stop to check that the nut moves freely to be sure you're not swelling the crank. Do not use a torch to heat the fly wheel or the crank. Your ignition system parts and upper crank case seal may be damaged. When the flywheel is off you might find that the moon key is sheared. When you put it back on, as you alighn the key and lower it, the magnets will quickly pull it down and smash your fingers if you're not careful. We usually let this happen to new guys in the shop but if nobody's there to see it what's the point? On the other hand your problem could be elsewhere. Many small 4-strokes are equiped with compression relief systems to ease starting. I think they can act up if you're low on oil or not pulling it fast enough. Try turning over without plugs to see if you have a compression relief malfunction. With no plugs the compression shouldn't even come into play. If it still hangs up you have a mechanical problem and the removing the flywheel would be the next logical step. A sheared flywheel key could possibly act this way. Good luck and report back with any mysterious findings.
 
You took the plugs off to check the valves? Not sure what that means. Was this engine running at some point after you got it because you don't say.

I suppose it could be a broken charge or pulsar coil under the flywheel. This sounds EXACTLY like a valve is hanging open and the piston is contacting it. If it happened every revolution, I'd guess the engine wasn't timed correctly. But, since it only happens every so often then it sounds like a sticking valve or, a very worn or loose timing belt. You need to be VERY cautious about prying on the flywheel to force the engine past whatever is causing the hang up so that you don't do any more damage.
 
I too believe it could possibly be a valve. If so the damage is done, meaning that by forcing the engine to rotate past the point where the valve contacted the piston the valve stem would be bent. The pattern is troubling me. If there is a hangup it should do it every time or sometimes but to do it on a pattern suggests that the valve timing is off or there might be damage to the gears in the lower unit. The FWD, REV, and pinion remain engaged even when the engine is in neutral. 17+6=23. I could see 23 teeth on a drive gear in a small engine like this. You could try removing the lower unit and seeing if the engine turns over smoothly, simply having it in neutral will not work. I don't mean to throw a lot of speculation out there, just brainstorming. If you have'nt made any progress as of yet now would be a good time to pull the lower unit. With no spark plugs you should be able to turn the flywheel easily by hand.
 
Thanks for replying, the timing is way off. The marks on the cam pulley and flywheel are way off, the timing belt must have slipped alot. I use a flat head screw driver and hammer to push the belt off of the cam pulley. I lined up the 2 marks, no more hang ups, but would not start. Did a compression test, got around 20 psi for both cylinders, not good. I think the valves are bent. Now I gotta remove the flywheel to change the timing belt. Then i gotta get the cam pulley off and the head to replace the valves. It not going to be easy but I think I can do it...

Do I have to remove the cam pulley to change the valves???
How do you remove the cam pulley?
What is the normal COMPRESSION FOR A 1997 BF8AM LA???

Thank You so much for replying and helping...
 
Make sure you check compression with the throttle wide open. Compression should be about 142 psi.

You do not have to remove the cam pulley to remove the head. You also do not have to remove the powerhead from the motor.

It seems to me that the only time I changed a timing belt on one of these, I did not remove the flywheel. (My memory could be failing me, though).

Mike
 
I want to question you about how you determined that the timing was "way off". If you're not working with a manual, you could get it wrong.

There is a "T" mark on the flywheel that lines up with a "protrusion" on the recoil starter bolt boss on the engine's center line. The cam pulley has a "#1 and a "#2" marker but they line up with a "T" mark and arrow on the cylinder head that is about 20 degrees to port of the engine's center line. They DO NOT line up with the engine's center line or flywheel markings. Lots of guys get that wrong when "wingin' it" so I'm just trying to watch your back here.
 
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