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B&s 21Hp V-Twin Troubles


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#1 DH1 ONLINE  

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Posted May 01, 2013 - 08:06 PM

How I fixed and engine with a 2lb sledge hammer.

 

One of my neighbors has a JD lawn tractor bought from Home Depot 4 or 5yrs ago.

Calls me and says he blew up the engine and wants to know where to get another one.

So I go over, take a look and battery dead, N/G, we boost the battery, get it running but only on 1 cylinder, I switch spark plugs and again only 1 cyl, same one hitting.

I check spark on the dead cyl, it's good, pull the plug and check compression with my finger over the spark plug hole and it has compression.

Next I pull off all the covers and find a mouse nest on the fins of the dead cyl. Cleaned all that out.

So why is this cyl not fire-ring? I pull off the  valve cover and find 1 bent push rod for the exhaust valve.

I try to push the exhaust valve down, it doesn't move.

So I remove the cyl head and still can't move the exhaust valve, try some penetrating oil, no luck.

Next I remove the rocker arm and hit the end of the valve with a 2lb hammer, 1 careful firm tap. Now the valve moves free but only a little bit.

I then look at the guide and find that it seems to be not in place where it should be, too close the the small end. I remove the valve spring and retainers with my fingers, not easy to do but got them off.

I then take a small deep socket and pound the guide back in place with my 2lb hammer till it looks like the intake guide does.

Valve moves free and the same as the intake does.

I then take the push rod and pound it back straight with my 2lb hammer best I can to make it straight. No harden metal in these push rods.

Put the motor back together, try to start it and it fires right up, both cylinders hitting smooth and steady.

All this done with buying or replacing any parts.

Will see how long it lasts.


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#2 IlovemyCub OFFLINE  

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Posted May 01, 2013 - 08:14 PM

Interesting story! Thanks for sharing, Ian. 



#3 superaben OFFLINE  

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Posted May 01, 2013 - 08:16 PM

Same fix worked for a 16 OHV Vanguard.  As far as I know it is still in operation.  Not the service manual's way, but that try sure beat the heck out of the redoing or replacing the head.

 

Ben W.



#4 olcowhand ONLINE  

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Posted May 01, 2013 - 08:18 PM

If it does it again, I'd replace the guide & put the strongest Loc-Tite to help hold it.  Likely this will last a long time though.



#5 DH1 ONLINE  

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Posted May 01, 2013 - 08:21 PM

I figure the mouse made the nest, the next time they used it that cylinder overheated, the valve guide moved and bent the push rod, shutting down that cylinder


Edited by DH1, May 01, 2013 - 08:24 PM.


#6 olcowhand ONLINE  

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Posted May 01, 2013 - 08:23 PM

I figure the mouse made the nest, the next time they used it that cylinder overheated, the valve guide moved and bent the push rod.

 

Yep, the high heat caused it for sure.  



#7 skyrydr2 OFFLINE  

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Posted May 02, 2013 - 03:12 AM

Did you sand the head surface flat ? It will blow a head gasket next if it wasn't done. That is the number one reason these things fail or are found at the scrap yard LOL " it blew up" the owner would say as he dropped off a brand new looking rider.

#8 1978murray OFFLINE  

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Posted May 02, 2013 - 08:33 AM

the guides in briggs suck. the best way to get them to stay in is fold the metal in around them with a punch



#9 KennyP ONLINE  

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Posted May 02, 2013 - 08:44 AM

I keep a couple 3 & 4 lb. hammers around to 'fix' things! :bigrofl: Way to go, Doug!



#10 JD DANNELS OFFLINE  

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Posted May 02, 2013 - 09:40 AM

I had an intake stick on my Murray last spring. was running on one cylinder and blowing back through the intake.

 Was showing my dad what it was doing and we were about to pull off the head.

Dad said start it one more time and the valve came loose and it ran fine. I  put a little MMO in the fuel and in the oil(assuming carbon buildup?) and it has ran fine ever since. And I don't baby it, I'm likely to run it a couple hours at time without shutting down till I need fuel.



#11 DH1 ONLINE  

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Posted May 16, 2013 - 09:28 PM

Update

 

Well it didn't last long, he used it about 10 to 15hrs and it broke again.

Last weekend I got the call, broke again, so I took off the valve cover and sure enough 2 bent push rods.

I told him to get 2 new push rods and gave him the #s needed.

I removed the head, removed the exhaust valve, and the guide. Cleaned the head and guide best I could and reinstalled the guide with Red Permanent locktight, as was mentioned earlier, let it sit for 1 day and put the engine back together, this time I set the valve clearances also.

So far so good, will see how long it lasts, if it fails again, I'm at a loss as to how to fix it.






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