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Carb screw damage to piston & cylinder head.


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#1 TGaffney OFFLINE  

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Posted May 24, 2017 - 10:05 AM

A couple of weeks back my Bolens 1220 with a Tecumseh 12 horse started running roughly.  I found the carb plate loose and both brass screws missing.  I replaced the screws (added loctite) and went back to tilling.  Then I got to wondering where did those screws go?  Could they possibly have worked their way into the cylinder head?  Looks like the answer is yes. 

 

I was thinking of flattening the head, replacing the gasket, and hoping for the best.

 

Any other ideas as to what I should/should not do at this point?IMG_1974.JPG

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#2 KennyP OFFLINE  

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Posted May 24, 2017 - 10:24 AM

Id be more worried about that piston than anything. Could have pinched the top ring!


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#3 secondtry OFFLINE  

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Posted May 24, 2017 - 10:27 AM

  Run the piston down and check fore cylinder damage. Check for cylinder ridge indicating wear. Find an appropriate feeler gauge to try to determine if the top of the piston has been beaten over and made to rub. Run the piston down then use a magic marker to paint the inside of the cylinder, let it dry well and run the piston up and back down to try to find any thing that is rubbing excessively. Don


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#4 MiCarl ONLINE  

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Posted May 24, 2017 - 11:34 AM

I'm an "if it ain't broke don't fix it" guy.  If the bore passed a visual inspection I'd put it together and worry about it when/if an issue turns up.

 

If you got the screws back intact they likely didn't do anything to the rings.


Edited by MiCarl, May 24, 2017 - 11:35 AM.

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#5 boyscout862 ONLINE  

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Posted May 24, 2017 - 11:46 AM

I tend to be conservative. I would take the engine apart and recondition the head and piston. Imperfections in pistons tend to focus forces so that the imperfection becomes the initial failure point. Often a little filing and sanding can grealy improve the  situation. Those engines are getting harder to find so, what we have need to be babied. Good Luck, Rick


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#6 Rainier OFFLINE  

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Posted May 24, 2017 - 12:18 PM

If the cylinder wall is ok, then I would just run it. I've seen worse than that and they are still running fine.
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#7 TGaffney OFFLINE  

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Posted May 24, 2017 - 12:54 PM

Thanks for the input & advice gents. 

 

I turned the flywheel and inspected the cylinder and did not notice any scoring.  I will try the marker trick to see if there are any "high spots" on the top of the piston.

 

Absolutely no idea what become of the screw or screws. I didn't find them when I took of the head. 


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#8 classic ONLINE  

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Posted May 24, 2017 - 01:37 PM

The screw or screws went out the exhaust and can be found in the muffler sometimes. You should check your valve seats and valves for damage in case a screw got pinched between them on the way out. I have some NOS standard HH120 pistons if you find yourself in need of one. I too am betting that at least the top ring is pinched in it's groove. I wouldn't run the engine as is, since they are very easy to work on and make things right.

Edited by classic, May 24, 2017 - 01:38 PM.

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#9 olds45512 ONLINE  

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Posted May 24, 2017 - 01:57 PM

I'd clean it up and run it. If the cylinder wall isn't marked up the it will be fine, if you must you could replace the head.

Edited by olds45512, May 24, 2017 - 02:04 PM.

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#10 Cnc ONLINE  

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Posted May 24, 2017 - 02:11 PM

The exact same thing happened to an HH120 in my massy a number of years back. One choke screw voyaged through the top end and bent the exhaust stem enough that the valve would not seat well. I put a new valve and lapped it and all was well. What ever else you do to repair the motor, make sure the replacement screws are well staked or well penned to prevent a second incedent.
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#11 EricFromPa ONLINE  

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Posted May 24, 2017 - 02:13 PM

I would pull the piston and check the rings. If the compression ring got pinched hard enough it could of snapped it. Cast iron rings snap really easy. 

 

Check your valves and valve seats carefully. Also Spin the valves and see if they are bent. Doesn't take much to bend a valve.

 

 

Is that an old crack on your head going from the spark plug hole to the bolt hole or just flash from casting?


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#12 karel OFFLINE  

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Posted May 24, 2017 - 02:53 PM

If it didn't get smashed beond the compression chamber, I'd give the bore a little file and throw in a new piston. might as well peek at the lower end while your into it.


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#13 MiCarl ONLINE  

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Posted May 24, 2017 - 03:56 PM


 

Is that an old crack on your head going from the spark plug hole to the bolt hole or just flash from casting?

I missed that and overlooked that the valves had hammered the screws against the head.  I'll bet it's a new crack and the valves are likely bent.


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#14 TGaffney OFFLINE  

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Posted May 27, 2017 - 08:54 PM

Thanks for the extra input and advice.  I somewhat smoothed out the head and put it back on today with a new gasket.  I will have to do a compression check and report back what that is.

 

I didn't notice the crack in the head  behind the plug and between the valves.  Not sure if that goes all the way through or not.

 

Both valves spin freely - so I guess that is a good sign.  Also I did the marker test and I noted two points where there was a hairline width or so erasure of the marker.  Maybe from the top of the piston being deformed in those areas? 

 

I will check the muffler for the brass screw(s).  I hope they made it that far and aren't in a place where what is left of them can pop back into the cylinder area.  I used lock tite on the new brass bolts/screws holding the choke plate.  Hopefully they hold!  


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#15 nkaust ONLINE  

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Posted May 27, 2017 - 09:40 PM

if you need an another head let me know i have an extra


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