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I had a honda lawn mower that had a bent crankshaft. I ordered a new shaft and put it in. However, after putting the engine back together it is kicking back when I try to start it. I timed the cam the way I have read that you should do with the piston being at TDC and the two marks on the cam gear being parallel with the the block. It will start and runs fine but sometimes when trying to start it, it will try to pull your shoulder out of its socket. Would having the belt one notch either too slow or too fast cause this? It has got me beat as I have tried everything I can think of and can't seem to eliminate the kicking back. I did check and the decompression arm is opening the exhaust valve up just a little bit to relieve the compression. Any help would be greatly appreciated.

If the jerk back is associated with a pop or bang then it is out of time
If it just stops dead then recoils then the decompressor is not working.

They feel very similar.
the first is because the engine is firing at the wrong time so you just get a jerk while the rope is pulling
The second is because you can not get the piston over TDG so it gets harder to pull then stops then pulls back.

In the timing case it will be because the engine is too far advanced.

A split or broken timing key in the flywheel will do the same thing so check it before you go ripping into the engine again.

bertsmobile1 said:

If the jerk back is associated with a pop or bang then it is out of time
If it just stops dead then recoils then the decompressor is not working.

They feel very similar.
the first is because the engine is firing at the wrong time so you just get a jerk while the rope is pulling
The second is because you can not get the piston over TDG so it gets harder to pull then stops then pulls back.

In the timing case it will be because the engine is too far advanced.

A split or broken timing key in the flywheel will do the same thing so check it before you go ripping into the engine again.

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I had the key out when I replaced the crank and didn't notice anything wrong with it. I did find it a little strange that it appeared to be steel not an aluminum one like in most Briggs engines. With the valve cover off and the plug out I have rotated the engine several times and the decompressor appears to be working in that it appears it opens the exhaust valve maybe an 1/8 of an inch. Do you think if I advanced the timing gear one notch on the belt it would possibly open the exhaust valve a little quicker and therefore it would not kickback? I'm not even sure if it would run in that position or not as I tried to set it up just like it says to put it in time. It runs great when you can finally get it passed the hard spot and get it to start. I failed to mention that there is no popping or anything noise at all when it does this other than me uttering a few choice words when it jerks the cord out of my hand.

Is this a GVC engine?
Are you attempting to start without blade attached?

Russ2251 said:

Is this a GVC engine?
Are you attempting to start without blade attached?

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No the blade is attached although the mower does have a blade clutch so the blade isn't actually turning when trying to start it. It is a GVC 190 engine. The funny thing about this is it didn't do this before I replaced the crankshaft.

mower does have a blade clutch so the blade isn't actually turning when trying to start it.

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Known as BBC or Blade Brake Clutch.
Can blade be engaged whilst attempting to start?
If so...try that.

Russ2251 said:

Known as BBC or Blade Brake Clutch.
Can blade be engaged whilst attempting to start?
If so...try that.

Click to expand...

I will try that tomorrow. I talked to the guy I got the mower from (the one that bent the crankshaft) and he said he never had any problem with it doing anything like this before he hit something and bent the crank.

:welcome: Welcome to the forum!

I'm going to move this thread over to our Honda section.

I think Bert is referring to spark timing, not cam angle. The spark timing would be affected by flywheel key , different flywheel, loose flywheel , different coil pickup geometry, loose coil mounting? On Briggs V engine I can hook up an auto lite and it will fire dull red in a darkened garage. Since there is no advance (Honda?)when the engine turns fast enough to generate spark you could see where timing is, but you must first mark TDC.

motoman said:

I think Bert is referring to spark timing, not cam angle. The spark timing would be affected by flywheel key , different flywheel, loose flywheel , different coil pickup geometry, loose coil mounting?

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Do you know if I advance the cam one or two notches on the belt wouldn't that retired the timing? Also, do you know how many notches I could move it and it still run? Thanks

With the move to Honda forum I think someone there wlll give you detailed advice.

I'm still fighting the battle and I think it is going to win. I'm beginning to wonder if the flywheel keyway in the crankshaft I bought could be off just a little bit causing it to be out of time just enough to kick back when trying to start it. I did figure out that when I shut the engine off if I will turn the gas off and let it burn all the fuel out of the carb then when I get ready to start the next time that It does not kick back. Maybe that is customary with an engine that is out of time, I don't know. I hate to tear the engine down again and replace a new crankshaft but I've about exhausted every idea that I can think of that could be causing this other than a mismanufactured crank. Does anyone have any other ideas as to why I would be getting the kickback other than being out of time and is there anyway to correct this other than replacing the crankshaft?

Did you try to start it with blade engaged?

Russ2251 said:

Did you try to start it with blade engaged?

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Yes it doesn't make any difference.

Here are correct timing pics for any GCV Honda:

Russ2251 said:

Here are correct timing pics for any GCV Honda:
View attachment 39924View attachment 39925

Click to expand...

That is the first time I have seen the picture of the crankshaft with the arrow on it. What I had seen is lining the keyway slot on the crank with the centerline of the block which I think is basically the same. I guess I am going to have to tear it down again and I will check the arrow at that time. Thanks for the info. Fortunately I still have the old crank that was bent and I will compare everything including the position of the flywheel keyway with the new crank. I appreciate your efforts and knowledge on this.

This may or may not help, but I've had a couple of GCVs start kicking back on start-up and a tight-ish valve adjustment fixed them. Thought it might be worth a try before tearing the engine back apart.