Briggs 17.5 HP, OHC Engine Locks Up!

brchad

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ENGINE:

Briggs & Stratton, 17.5 HP
31C707 3346 G6
Code: 110224ZB 23882

Just as an introduction, I'm 70 and have been working on small engines since I was 10 years old. My employment background was sales and maintenance for two different pump companies in the Petro-Chem market .... specialty engineered centrifugal pumps for hazardous liquids (canned motor pumps and magnetic drive pumps.) With all that said.... I'm totally baffled by this problem with a Briggs & Stratton one cylinder engine! I've run out of ideas!

I've had the typical problem that's so prevalent on the web: the ridiculous compression release system and was fortunate enough to run across your instructions for setting the valves at 1/4" past TDC compression stroke. That saved me from replacing the third intake push rod and I began checking valves .... sometimes twice per season.

In spite of all my maintenance efforts, I had used the mower, shut it down.... went to restart it a week later and got the "lock up" when starting with a good battery. I tried setting and checking the valves about 10 times before I took the engine off and opened the sump. Sure enough.... there was those pieces of the compression release mechanism in the bottom of the case.

I purchased a new camshaft and installed it per factory manual.... lining up timing marks, etc. When I mounted it on the mower, I tried turning it CW by hand. It turned several revolutions and then FROZE (CLANK) in one place. I pulled the sump back off and saw that the timing marks (Crankshaft and Camshaft) were aligned .... piston about half way down. Just jammed. I stripped the engine down to the short block (not removing connecting rod, piston, counterweights, etc.) including the head. Took the head off, tappets out, rods out, etc. (New oil all over everything by the way.) I inspected the Crankshaft timing gear... I see no visible signs of wear. (I have a new one on order anyway.)

This is NOT the compression release problem.... where the engine hits the compression stoke and it's difficult to turn. When I say FROZE .... I mean it's JAMMED.... and will not turn forward period. The only way to unlock it, is to use channel-lock the shaft and turn it backwards. Then, if it's moved CW again .... it locks up.

Here's a weird piece of information: If I put the Camshaft in a random position (out of time in other words) the engine turns CW freely and doesn't gall up. Very strange.

Any suggestions, ideas, wild guesses, etc. would be great.

Thanks
 

EngineMan

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ENGINE:

Briggs & Stratton, 17.5 HP
31C707 3346 G6
Code: 110224ZB 23882

Just as an introduction, I'm 70 and have been working on small engines since I was 10 years old. My employment background was sales and maintenance for two different pump companies in the Petro-Chem market .... specialty engineered centrifugal pumps for hazardous liquids (canned motor pumps and magnetic drive pumps.) With all that said.... I'm totally baffled by this problem with a Briggs & Stratton one cylinder engine! I've run out of ideas!

I've had the typical problem that's so prevalent on the web: the ridiculous compression release system and was fortunate enough to run across your instructions for setting the valves at 1/4" past TDC compression stroke. That saved me from replacing the third intake push rod and I began checking valves .... sometimes twice per season.

In spite of all my maintenance efforts, I had used the mower, shut it down.... went to restart it a week later and got the "lock up" when starting with a good battery. I tried setting and checking the valves about 10 times before I took the engine off and opened the sump. Sure enough.... there was those pieces of the compression release mechanism in the bottom of the case.

I purchased a new camshaft and installed it per factory manual.... lining up timing marks, etc. When I mounted it on the mower, I tried turning it CW by hand. It turned several revolutions and then FROZE (CLANK) in one place. I pulled the sump back off and saw that the timing marks (Crankshaft and Camshaft) were aligned .... piston about half way down. Just jammed. I stripped the engine down to the short block (not removing connecting rod, piston, counterweights, etc.) including the head. Took the head off, tappets out, rods out, etc. (New oil all over everything by the way.) I inspected the Crankshaft timing gear... I see no visible signs of wear. (I have a new one on order anyway.)

This is NOT the compression release problem.... where the engine hits the compression stoke and it's difficult to turn. When I say FROZE .... I mean it's JAMMED.... and will not turn forward period. The only way to unlock it, is to use channel-lock the shaft and turn it backwards. Then, if it's moved CW again .... it locks up.

Here's a weird piece of information: If I put the Camshaft in a random position (out of time in other words) the engine turns CW freely and doesn't gall up. Very strange.

Any suggestions, ideas, wild guesses, etc. would be great.

Thanks

I would remove the piston with connecting rod then see if you can turn it over without problems, if still jammed remove the camshaft and try again, (that is if you already haven't done so) if still jammed remove the push rods and try again, remove one item at a time that way hopefully you see where the problem is. (before removing the piston put a mark on it and on the top of the cylinder) am sure you know anyway. come back with your findings..!
 

brchad

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I would remove the piston with connecting rod then see if you can turn it over without problems, if still jammed remove the camshaft and try again, (that is if you already haven't done so) if still jammed remove the push rods and try again, remove one item at a time that way hopefully you see where the problem is. (before removing the piston put a mark on it and on the top of the cylinder) am sure you know anyway. come back with your findings..!

EngineMan -

Thank you for your response. I think we are on the same page regarding the process of troubleshooting mechanical equipment. For me, the three most important steps of the process are: 1.) Make sure you fully understand the nature of the problem... symptoms, timing, etc. 2) Double check ALL assumptions. (False assumptions can spoil and chance of success.) 3.) Investigate by process of elimination. What follows is a list, beginning with the occurrence of the problem to where I am as of now:

1. A couple or three years back.... while mowing (Troy-Bilt) the engine simply stopped. Simple investigation determined that the intake push rod was broken. I replaced the rod, set the valves but when trying to start, the engine would begin to turn and then lug. In short.... this is when I learned about what I see as a pathetic compression release system.... that I'm sure you are familiar with. (I couldn't believe that B&S had actually allowed that design on the market.) After resetting the valves at the 1/4 off TDC mark.... I was off and running. I then began to check the valve settings at least one or two times per season.

2. A few weeks ago.... I had the same experience.... this time it had run fine and I shut it down after mowing. When I tried to start it a week or so later.... lug again just as before. I first checked the battery (almost new), cables etc. Nope. So I immediately checked the valve settings. They seemed like perhaps they were a tad off.... so I reset them... again using the 1/4" off TDC. I set them perhaps 8 times. Still no luck.

3. Having read previously about the compression release system problems with the cam, I pulled the engine, removed the sump .... and BINGO .... there were the notorious broken pieces of the timing "spring lever" in the bottom of the case. I removed the cam.... and saw where the lever used to belong. I ordered a new cam, gaskets, etc.

4. While waiting for the parts, I thoroughly flushed the case with oil. I had kept the broken pieces, making sure I could account for any missing pieces that may have logged somewhere. Flushed the engine a second time and mopped it completely. Bear in mind that prior to this point... the starter would easily rotate the engine freely when the spark plug removed and by hand. When I installed the new cam.... I followed normal procedure to install and time.... cam and crankshaft gear timing marks lined up. This part may be critical: I noted that my attempt to place the crankshaft with the timing mark pointing toward the centerline of where the cam shaft goes .... I found it impossible to simply drop (wiggle) the cam into place. It was necessary to turn the crankshaft (CW when looking down at the flywheel) somewhat .... and offsetting the cam so that after it was installed and rotated, the timing marks would line up.

5. When everything looked all good.... having replaced and checked the governor setting .... new gasket, new seal .... lubed everything ... dropped the sump on .... wiggled the crankshaft and the sump fell into place. After having it all buttoned up was when I discovered that it would rotate (CW) somewhat.... then a CLANK ... and stop. If I rotated it backwards with channel locks it would break free. Regardless of how far I turned it in reverse.... it would still CLANK in the same place.

6. I removed the sump cover while the shaft was in the jammed position.... and noted that it was exactly when the timing marks were aligned.

7. At this point I began the process of elimination as noted in my original post. First removed the cam, of course.... and all turned fine without the cam. Replaced the cam.... CLANK. Removed the cam again... removed the rocker arms, push rods from the head and the valve tappets from the case. Everything still totally free with no cam. Installed the cam .... CLANK. I removed the head to watch the piston and movement appeared normal. (The head had the typical and expected amount of grime, easily removed and cleaned.)

8. I removed and inspected the crank shaft timing gear. It showed no visible signs of wear. Not assuming it was good.... sometimes it's difficult to see or feel a faulty part .... I ordered a new one, which will be arriving on Monday.

So... that is where I am in the process as of now. I will say that I seriously doubt that the new crankshaft timing gear will solve the problem.... but that's just an assumption! LOL!!

Again.... thank you for the response. One final step in my process came after fighting it for years. Don't be too proud to solicit advice! I continue to welcome ANY and ALL questions, comments or potential solutions.

Regards,

Bill
 

EngineMan

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When you go to put it back together refit the camshaft and remove the head and leave the push rods out, then try to see if you turn it in both directions, if so refit the push rods and head and try again, am thinking maybe the push rod(s) lifting too far up and pushing the valves or valve too far out and hitting the piston, so it maybe a wrong size push rod..!, try it with the arm-rockers off, come back and let us know. good-luck.

"6. I removed the sump cover while the shaft was in the jammed position.... and noted that it was exactly when the timing marks were aligned."

This would be near or at TDC
 

BlazNT

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Check for all gaskets to be in place. Could be one not installed so not enough clearance.
 

brchad

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When you go to put it back together refit the camshaft and remove the head and leave the push rods out, then try to see if you turn it in both directions, if so refit the push rods and head and try again, am thinking maybe the push rod(s) lifting too far up and pushing the valves or valve too far out and hitting the piston, so it maybe a wrong size push rod..!, try it with the arm-rockers off, come back and let us know. good-luck.

"6. I removed the sump cover while the shaft was in the jammed position.... and noted that it was exactly when the timing marks were aligned."

This would be near or at TDC

Thanks EngineMan -

I double checked the push rods.... same as the old ones.... same part number, etc. I already removed the head.... so no push rods.... no tappets. Still the same problem. So I can clearly see where the piston is. You did provide a clue here. Indeed, the timing marks are aligned, but I need to double check the piston position in the locked position with timing marks aligned. If I remember correctly, it is not at TDC .... but I have to double check. I'm not able to do it now... but will check it tomorrow after church and report back in early afternoon.

Thanks!

Bill
 

brchad

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Boobala,

Hey.... my wife of 47 years doubts my competence and/or abilities all the time! I try to make it a point not to work when she is around! :)

Yes... thanks... I DO have the manual ... but thanks for the link. I'll check to see if it's the same version/revision, etc.

I appreciate the help.

Bill
 

brchad

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Check for all gaskets to be in place. Could be one not installed so not enough clearance.

All new gaskets.... all in place.

Thanks,

Bill
 

brchad

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Bill I am NOT doubting your competence or abilities OR that of anyone else posting on this thread, I expect you have the Briggs O/H manual, if not, here it is ........

https://drive.google.com/file/d/0B6NaqjIxWV1ybEN0LWo3azl6OUU/view

Hope you fix the issue and keep us posted.... Boobala

Boobala -

Not to worry. My wife of 47 years doubts my competence and/or ability all the time. I make sure to work when she isn't around. LOL!

I do have the manual.... but I'll check to see if I have the current version.

Thanks,

Bill
 
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