875 redo

[Ed Kennell 35,919]

Yep, that's gotta be the reason it won't run.

I also found the intake valve had 0.001" clearance , so I ground the stem to get 0.006". The exhaust was Ok.  Would It have been built this way or is it common for the intake to loose clearance? 
Also found the points were set at 0.009".  Cleaned and reset to 0.020".   


One side of the hood bracket was broke off  , so I fixed that while waiting for new engine parts delivery.


The holes in the hood bracket were really wallowed out, so I drilled them out to 1/2" and installed 1/2 X 3/8 bushings made from nylon tubing,  then welded on brackets for a 3/8" hinge pin.



" THATS ALL FOLKS"                Mrs K just  called     dinner.


 

[slammer302 2,154]

More than likely the valve has worn down and made its way closer to the lifter tappet and the points lobe on the cam might be worn Sent from my XT1080 using Tapatalk

[Ed Kennell 35,919]

More than likely the valve has worn down and made its way closer to the lifter tappet and the points lobe on the cam might be worn Sent from my XT1080 using Tapatalk

I was just surprised the intake had no clearance and the exhaust clearance was correct.    The PO said it ran fine and he was mowing when he heard a "BANG" and it quit running.
These little horses are pretty tough to keep running with the points and valve clearances out of adjustment sooo bad.
I wonder if these problems could have caused the rod failure ?    Although it was dirty, there was oil in the engine when I tore it down.

[MikesRJ 552]

I would highly suggest that while you have the engine apart, locate the T & A timing marks on the back side-edge of the flywheel and lightly sand the area of both. Then paint the letters with white paint so they are highly visible. This will facilitate mechanically timing the engine, and if you have an inductive timing light, you can fine tune the gap after she is running.

[Ed Kennell 35,919]

Will do...Thanks Mike.

[MikesRJ 552]

Not knowing if you know how to statically time the engine, here is a link to the procedure. This gets you "very close", the inductive timing light will get you spot on after it has been mechanically timed. Normally I've found that a few thousandths one way or the other gets you "spot on".

KOHLER K SERIES STATIC TIMING
http://mgonitzke.net16.net/tools/static_timing.pdf

[slammer302 2,154]

I recommend checking the governor gear. Dirty oil can really wear away the teeth on the plastic ones you may get lucky and have the metal one.

[Ed Kennell 35,919]

I would highly suggest that while you have the engine apart, locate the T & A timing marks on the back side-edge of the flywheel and lightly sand the area of both. Then paint the letters with white paint so they are highly visible. This will facilitate mechanically timing the engine, and if you have an inductive timing light, you can fine tune the gap after she is running.

Mike, I can only find these two marks.    The one with the T and another about 10 degrees ccw from the T mark.
My points break on the VOM a couple degrees past the second mark.  So to confirm, I need to close the gap so they break on the T mark??
Pardon my art work.

[MikesRJ 552]

You're close. The T mark is TDC, or "Top Dead Center", and the A mark is the one without a letter and indicates 20 degrees before TDC. Time, per that instruction, to the unmarked line. That is also the line you will fine tune the timing to when using an inductive timing light. Remember that opening the points advances the timing and closing them retards the timing. So based on your picture you are too advanced right now. I'd adjust it per the procedure then use the light to get it spot on once it's running.

Edited July 22, 2015 by MikesRJ

[Ed Kennell 35,919]

Got it Mike..Thanks.   So that's probably why the PO had the gap set at 0.010" .
I will set it tomorrow and let you know what gap I end up with.  Is there a minimum gap?
I'm not sure I could see the timing mark with a timing light after the engine is assembled in the tractor.  Seems the starter is in the way.  Maybe with a mirror.

[MikesRJ 552]

0.020" gets you in the ball park, setting by the written procedure gets you closer, but the timing light gets you spot on. I've seen them as low as 0.010" and as high as 0.030" but it really depends on the engine. Based on where it's set now you might want to measure the pin behind the points and make sure its length is correct. It might be a tad short based on the points gap you have now.

Edited July 25, 2015 by MikesRJ

[953 nut 51,940]

    I knew that ignition timing was set by points gap but never knew about the static timing. Thanks for passing this along.

[Ed Kennell 35,919]

  

 I knew that ignition timing was set by points gap but never knew about the static timing. Thanks for passing this along.

     Same here Richard.    

OK Mike, I had to set my point gap to 0.015 to get them to "break" on the 20 degree mark.    Not too bad, so my pin is probably OK.
Please correct me if I'm wrong Mike, but isn't the 20 degree mark past TDC not before ?  Isn't the goal to have the plug fire just after TDC ?  It just doesn't seem correct to have ignition with the piston still moving up
If so, it  seems to me using a dial indicator to measure the piston height would be a more accurate way to position the piston in the correct location for  setting the points to break.
This would eliminate any inaccuracies  in the location of the timing marks on the flywheel or its timing with the crank, etc.
Is there any data on ultimate piston height position  before or after TDC for plug firing?
Thanks again for the education Mike.    Not trying to reinvent the wheel here, but always looking for a better way.
 

[bmsgaffer 2,043]

Someone smarter than me may come in here and give some more insight, but here's my take:

The combustion of the gas and air actually takes time from beginning to full expansion. You have to time the explosion to be used up to its fullest in one down stroke of the piston. To do this, the explosion is started just before TDC (keep in mind at 20° before TDC the piston is not really moving up much at all, its VERY close to full stroke). The inertia of the flywheel is enough to overcome the minimal pressure at this point and the combustion should be in full force by the time the piston starts heading back down. At 3600 RPM that piston is going through one combustion stroke in just 1/60th of a second.

If you time it too early then you will 'ping' and the explosion will work too much against the inertia and you will loose some power, if its too late then you will be sending some of the still active explosion right out the exhaust stroke (open valve) and loose power that way.

Edited July 23, 2015 by bmsgaffer

[MikesRJ 552]

BMSGaffer is correct! Using a timing light and the B-TDC ("A" mark) mark is the most accurate. But I have found that once I know the gap with a timing light, I use a sharpie and write it on the inside of the points cover. Then when I replace points I go to that gap and check with a light. Rarely wrong until the engine is rebuilt again. And if it is wrong, it's one 1 or two thousandths off.

Edited July 24, 2015 by MikesRJ

[Ed Kennell 35,919]

Thanks Brandon and Mike,  for taking the time to explain the process and setting me straight.     Obviously, this is my first attempt at a rebuild and I really appreciate the advice.
Hopefully others on here will also benefit from this discussion.

[JPWH 5,312]

Very educational for me too! Thanks

[Ed Kennell 35,919]

   Looky what was in my mailbox tonight.       @‌$26  + $4 shipping  all the way from China in 3 days.


The bores look good and are in tolerance.     Just a few more questions before I start assembly tomorrow.
These edges at the cap splits have a noticeable burr that I will remove, but, should  there be a chamfer stoned on these edges to facilitate the lubrication?


I understand the oil hole must face toward the valves and with the old style piston that I have, It does not matter how the piston is oriented.
The thing I an not positive on is, the manual lists different torque settings for posi-lock or cap screw.   I assume I have the cap screw and should use the 200"lb setting.
The old rod had a flat sheet metal keeper.. I assume that is the posi-lock.   So with the cap screw, I over torque 20% to 240 "lb, then release and retorque to 200"lb.
 

Edited July 23, 2015 by ekennell
missed a word

[MikesRJ 552]

Here's the two manuals I have always gone by when rebuilding. Always have over-torqued 20% and re-torqued to spec., as suggested in the newer manual (2nd one). Never did notice any burrs so never did any of that.

http://www.mywheelhorse.com/graphics/file/Engines/Kohler_K91-141-161-181-241-301-321_1972-SM-2.pdf

http://www.mywheelhorse.com/graphics/file/Engines/Kohler_K91-141-161-181-241-301-321-341_tp_2379_SM.pdf

This time of year just make sure to fill the engine with straight 30w oil, run for 5 hours with the deck engaged, and then do an oil change.

Edited July 24, 2015 by MikesRJ

[Ed Kennell 35,919]

Got the 875 together today.
     Had to hand feed her for about 30 seconds and then she ran on her own kinda rough for a minute,then smoothed out and now really sounds like a happy little horse.

I wanted to try the hydro before I invested much time in the redo.   When I engaged the hydro she would barely move forward or reverse and had a funny tinny noise coming from the tranny.
This was my fear buying a non running tractor....a bad hydro. 
  The drive  belt seemed loose, so I loosened the engine bolts and moved it forward as much as I could to help  tighten  the belt.  

  Still no better, then I remembered this.





I had opened the tow valve to load it on the trailer. 
Closed the tow valve and tried her again.   Now I can even pop-a-wheelie although she isn't too fast and I still hear the tinny noise in the hydro.
I flipped the seat up and found the fan was missing a screw and the other three were loose.



That took care of the noise,  so we went on a 1/2 mile trail ride.

She runs fine and sounds good with the static timing setting, and the carb settings in the manual.

Thanks again to Mike and Brandon for all the help. 

    Now,  just need to decide what to do with  this one.

 

[squonk 39,006]

Love it! Those old Horse Hydro's use a fan off of a Refrigeration condenser to cool it! 

Edited July 27, 2015 by squonk

[AMC RULES 36,954]

   Ed, you have  trails?    

[Ed Kennell 35,919]

Love it! Those old Horse Hydro's use a fan off of a Refrigeration condenser o cool it! 

Yep, that's what it looks like Mike.  And I all ready got my fingers in it when I reached back behind the fender to disengage the hydro drive belt.  May have to fashion a guard for the fan to make it safe for the young-uns and the dummys.

[squonk 39,006]

I saw one of those at the show. I thought someone just threw a fan on it. 

Edited July 27, 2015 by squonk

[953 nut 51,940]

Got the 875 together today.
     Had to hand feed her for about 30 seconds and then she ran on her own kinda rough for a minute,then smoothed out and now really sounds like a happy little horse.

I wanted to try the hydro before I invested much time in the redo.   When I engaged the hydro she would barely move forward or reverse and had a funny tinny noise coming from the tranny.
This was my fear buying a non running tractor....a bad hydro. 
  The drive  belt seemed loose, so I loosened the engine bolts and moved it forward as much as I could to help  tighten  the belt.  

  Still no better, then I remembered this.





I had opened the tow valve to load it on the trailer. 
Closed the tow valve and tried her again.   Now I can even pop-a-wheelie although she isn't too fast and I still hear the tinny noise in the hydro.
I flipped the seat up and found the fan was missing a screw and the other three were loose.



That took care of the noise,  so we went on a 1/2 mile trail ride.

She runs fine and sounds good with the static timing setting, and the carb settings in the manual.

Thanks again to Mike and Brandon for all the help. 

    Now,  just need to decide what to do with  this one.

 

Ed, the Big Show theme tractor next year is CUSTOMS. With nearly a full year you could build a KOOL KUSTOM!