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Old 04-17-2012, 12:33 AM   post #1 of 21
sgokie
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Unhappy Engine Knocking Sound

For those of you following the restoration of my Dad's 30113S, I could really use your help.

I replaced the shear key on the flywheel tonight, and lo and behold, there was nice healthy spark from the plug. Buttoned everything up, added some gas, rechecked oil level and tried to start.

Got about two "putt-putts" from the exhaust, then began to hear large knock from engine case. I'm talking metal on metal sounding knock. When I removed spark plug and hand turned engine, no knocking sound. When I used starter and turned over engine for several seconds, no knocking sound. It was only when I put the spark plug in and put any compression on cylinder that banging sound started. I'm wondering if this may be why the first shear key sheared?

Any opinions? I'm really stuck on this one and deciding as to whether or not I have reached my technical ceiling. I pulled the cylinder head, and there were no scratches/scars on either of the valves or the piston. (Heck of a lot of carbon buildup as you can see from attached image).

If this was you, where would you go from here? If I choose to drop bottom case of engine to view crankshaft, connecting rod, etc., where do I get a good service manual?

This started as a labor of love, but I'm really frustrated being so close and now seemingly so far away to finishing. Thanks.
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Old 04-17-2012, 01:19 AM   post #2 of 21
WNYTractorTinkerer
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Icon2 Re: Engine Knocking Sound

The thing looks pretty carboned up.. Looks like a great opportunity to clean it up!

My question is why did the shear pin break? Was there a sudden stoppage due to tranny or PTO issue?? Or was it the flywheel coming into contact with something?

If that was the case the timing could be off which could cause 'spark-knock'..

So some more info on the engine's history wuld help a lot..

I'm sure someone else may chime in as well..
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Old 04-17-2012, 01:37 AM   post #3 of 21
sgokie
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Default Re: Engine Knocking Sound

Thanks for reply.

I pulled the flywheel to check/clean points and also to replace stator wire that was in bad shape. I don't know if the shear broke due to me putting it back in improperly, or something going on inside the engine, but I know that it was not due to any kind of pto, tranny or strike issue.

Before restoration, engine ran well with no knocks. A little smoke, but then again, it's over 20 years old, having sat unused in a garage for the last 10.

I don't know how "spark knock" sounds...this sound more metallic, growing more ominous the more I cranked the engine.

Thanks for reply.
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Old 04-17-2012, 07:46 AM   post #4 of 21
NOVAZ27
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Question Re: Engine Knocking Sound

Did your Dad ever give any reason why he parked the Snapper? You just may have found the reason he parked it. May be time for a repower or rebuild. Check the key again just to see if it is partially sheared. This could change the timing and could cause a spark knock.

JUST SOME THOUGHTS TO CONSIDER.
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Old 04-17-2012, 08:05 AM   post #5 of 21
Walt 2002
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Default Re: Engine Knocking Sound

"Before restoration, engine ran well with no knocks."

Well that sort of points to something you did. Did you check the coil armature air gap clearance after removing - replacing the flywheel? No loose magnets inside flywheel or broken bits of magnet? I don't recall what model your engine is but the flywheel needs to be wiped clean in taper and crankshaft the same then torqued to proper setting. Note that the key only aligns flywheel and crankshaft until nut is tightened.

I can send you a Service Manual covering the engine if you like. Address below, put in proper format and remind me, model number, etc.

Walt Conner
wconner5 at frontier dot com
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Old 04-17-2012, 09:29 AM   post #6 of 21
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Default Re: Engine Knocking Sound

Sounds like the syncro balance that is what happened to me.
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Old 04-17-2012, 10:09 AM   post #7 of 21
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Default Re: Engine Knocking Sound

If you don't want to separate the case for inspection, you could rotate the crankshaft to put the piston at 'mid stroke', and then slowly rotate the crank back and forth, with a little finger pressure on the piston, to determine if there is excess rod bearing or wrist pin clearance. You can rotate in one direction, to take up all the slack, and then do a little counter rotation, just enough, but not enough to move the piston, and then press on the piston to see if there is enough clearance for you to see the piston move. If the piston immediately starts to move in the when the crankshaft is rotated in the opposite direction, then there still may be too much clearance per the spec, but less likely enough to cause knocking when the oil is cold and thick, and I'd be taking it apart to see if the rest of the parts are still intact. A rod can knock for quite a while due to excess clearance potentially caused by 'someone' not checking the oil diligently every time before it gives up and dies. It will sound worse at low rpms, but can get to where you don't hear it with the engine at full speed.
I can't think of anything you could have broken internally, so I go with inspecting the flywheel and associated hidden parts. You can take the sparkplug out and rotate the engine by hand to see if you feel any interference or binding spots. You can even remove the valves and springs to minimize their effect to see if the crank and piston travel smoothly.
If you get enough carbon on the piston crown and cylinder head, you can get a knock that sounds like a rod bearing, from the piston poking on the head.
tom
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Old 04-17-2012, 11:42 AM   post #8 of 21
rscurtis
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Default Re: Engine Knocking Sound

Quote:
Originally Posted by BOSMECH View Post
Sounds like the syncro balance that is what happened to me.
That would be my vote too. If that's the case, it's time to look for another engine.
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Old 04-17-2012, 11:52 AM   post #9 of 21
sgokie
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Default Re: Engine Knocking Sound

Thank you all for responding!

Nova27, the Snapper was parked after my father passed away. My father suffered from Alzheimers and according to Mom, towards the end, riding this mower seemed to be one of the few activities he seemed to enjoy. This is why it I consider its restoration more a labor of love than of want. To my knowledge, there were no mechanical issues with the mower prior to its storage.

Walt, thank you for your offer of the engine service manual. I have emailed you at the address you listed with my information.

Yes, this problem is most likely due to something I did during the flywheel removal/reinstallation process. I did check the coil gap after reinstallation by using a "business card" between coil and flywheel. I cleaning everything on the top and bottom of flywheel. There were no missing magnets, nor evidence of any damage to the flywheel.

Also, please note that the flywheel on this model engine is held down by the bottom of the clutch starter assembly pressing against a concave washer...there was no separate bolt to torque. When I reassembled, I placed the flywheel back on the crankshaft, aligned the shear key notches, used punch to hammer back into place the shear key, placed concave washer back on crankshaft stem and spun on the clutch starter assembly by hand until snug. Then, I placed blunt end of chisel against a wing on the clutch starter housing and tapped it approximately one full revolution tighter on crankshaft stem. Could it be that I over/under tightened? Is there a specific torque setting for this action? How would I measure the torque for such an assembly? I've watched several videos on this procedure and don't remember anyone mentioning how much torque to apply...they just tighten an extra revolution after snug.

Tom Thank you for suggestion. At this point, I'm going to open the bottom case for a "look see". I'm going to need to acquire some tools for this operation, including feeler gauge, torque wrench and hub puller for the drive disc hub. I've had the hub soaking in WD40 overnight and hope it will come off tonight...it wouldn't budge last night. I can then open the bottom case and inspect inside. As you suggested, I will still try to test for the excess clearance when I get home tonight.

Thank you all again for responding!
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Old 04-17-2012, 02:09 PM   post #10 of 21
BOSMECH
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Default Re: Engine Knocking Sound

Synco Balance
Sorry been there done that 2 times.
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Old 04-17-2012, 03:07 PM   post #11 of 21
sgokie
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Default Re: Engine Knocking Sound

Pulled the crankcase cover over lunch and looked things over inside. I removed the oil slinger, cam shaft and both lifters. All appeared in good working order....no scars, pitting, etc. Filtered the drained oil and checked small amount of oil remaining in case when disassembled...also appeared clean, with no grit when rubbed between fingers.

Tried Tom's test, and pushing down on piston immediately rotated crank with no play in this action.

One thing I did notice was slight movement in the counterbalance assembly when rotating crankshaft. Is this supposed to move at all? Is this what you were talking about Bosmech?

Thanks again for your help.
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Old 04-17-2012, 03:19 PM   post #12 of 21
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Icon2 Re: Engine Knocking Sound

Movement of the counterbalance is probably a bad thing..

Pull off the rod cap off, push the piston to the top of the bore to gain clearance and remove the crankshaft (flywheel removed of course) and inspect for a broken, loose or twisted shaft in the rod mounting area. This thing may have suffered a hefty backfire.. Looks like there are some counter balnce gears or synchros as mentioned bove from the picture. The screw holding the plate on looks mangled a bit.. Has someone else been in it?

Post some pictures of what you found..
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Old 04-17-2012, 03:39 PM   post #13 of 21
sgokie
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Default Re: Engine Knocking Sound

Found this on net...a copy of a service manual page discussing synchro-balance on BS Engines. My engine model is 252707 series, which indicates it has the oscillating counterbalance system mentioned below. So, I guess from what it says, movement opposite the piston is the norm.

WNY, sorry bout the quality of my pictures. The bolt head has a phillips slot as well...that's what you may be seeing.

Thanks for reply!
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Old 04-17-2012, 08:59 PM   post #14 of 21
rscurtis
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Default Re: Engine Knocking Sound

The bottom counterweight bearing may be OK. It 's the upper that goes bad, and you have to remove the crankshaft to see it. IIRC the lower eccentric is replaceable, but the upper is part of the crankshaft.

Too bad you're so far away, I have a brand new Honda GXV 390 that would probably work on that mower.
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Old 04-17-2012, 10:22 PM   post #15 of 21
Walt 2002
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Default Re: Engine Knocking Sound

"How would I measure the torque for such an assembly?

B&S makes an inexpensive device that fits over the recoil clutch ***'y and use a socket with a torque wrench to torque. The Service Manual I sent MAY show it, will give the torque at least.

Gents, worn out counter balance bearings do not start knocking all at once as I said in my first post.

Walt Conner
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