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Farmall & IHC Tractors Discussion Forum
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MD compression

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Ray

02-03-2004 15:06:25




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Could somone tell me what the compression on an MD should be. Here's what I have #1 120, #2 100, #3 40, #4 140. The engine was stuck, Do you think we may have broke some rings or do you think we may have a burnt valve. Won't start either. Acts like its out of time. We have done everything we can think of but she just won't start.




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Farmaller

02-03-2004 18:26:34




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 Re: MD compression in reply to Ray , 02-03-2004 15:06:25  
It should start on gas fine , willmaybe miss alittle bit on #3. First make sure compression lever is opening the starting valves. You can check that by taking valve cover off. Have you checked for fire at the sparkplugs? Next check bottom of carburater to see if it,s getting gas. And what do you mean by acts like it,s out of time? And how did you get the motor unstuck?



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Ray

02-03-2004 19:48:50




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 Re: Re: MD compression in reply to Farmaller, 02-03-2004 18:26:34  
O.K. here we go. Just so you know everything the tractor was driven in to a garage about 3 years ago. Don't know if it was cooled down before it was shut off. Another thing we don't know is how the tractor was left, in gas or diesel mode, some say this may have an effect on the valves. Anyway the pan was removed and the rod caps on #1 and #4 were lowered about 1/4 inch or so and then the pistons were pushed up very carefully. Knowing these two were not stuck we tightened the caps pulling the pistons back down and then tried to get to #2 and #3. We modified (bent)a wrench an did the same to #2. It was stuck but not too bad. We couldn't get to #3 so we sprayed BP blast in the cylinder and let it sit for a few days.(#3 was stuck bad.) Then with the help of a big pipe wrench it finally turned over. In the last few days we have rebuilt the carb, put in new plugs, wires, cleaned up the mag, put in new points and condenser in the mag and installed a new cap and rotor. It took us a while but I'm quit sure we got it in time. How I know this is while turning the engine by hand when #1 come up to TDC the mag will light you up if you happen to he holding the plug wire. This is not funny. Now what I mean when I say it seems to be out of time is that it backfires. A lot. We have removed the breather and you can see down into the the carb and partly into the intake. While tring to start it up it will backfire back up this hole. What I'm thinking is its firing through a warped or possibly a burnt valve.#3. Thats why we only have 40lbs compression. Looks like we will pull the head in the next few days. Unless you may think its somthing else. sorry so long. THANKS

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Farmaller

02-04-2004 04:01:22




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 Re: Re: Re: MD compression in reply to Ray , 02-03-2004 19:48:50  
It sounds like it not timed exactly right. When no.1 is TDC you should be on pulley mark also. Then see where rotor is lined with mag cap. Remember trips at TDC on compression stroke. Then make sure plug wires in right order. mags on MD turns opposite. Doesn,t sound like it was stuck real bad so that is a good sign. However a lot of tractors were parked because of burnt valve. This thing should run. Keep in touch.

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Ray

02-04-2004 07:28:19




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 Re: Re: Re: Re: MD compression in reply to Farmaller, 02-04-2004 04:01:22  
Thanks a bunch! I'll post back when we get it running. I've learned a lot. Thanks again. Ray



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JD68

02-03-2004 16:43:04




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 Re: MD compression in reply to Ray , 02-03-2004 15:06:25  
Ray with that compresion you'll be lucky to start on gas, forget about going over to diesel.
Your description is a little vauge.
Be sure you have the starting handle in the diesel position when you do the compression test. I have the IH maual for the MD's and there is no compression spec listed but it needs to be at least 350 lbs for the fuel to ignite.
There are four starting valvesin the head that are opened up when the starting handle is pushed foward. This reduces the compresion so it will start on gas and warm up. These valves get sticky valve stems and don't close properly
which will keep the compression low. With 40 lbs in one cylinder it could be an intake or exhaust valve, or rings.
Well I guess you have alot of checking to do.
Good luck, there a great tractor when they run right.
BTW...when you do get it running,before you shut it down be sure to change back over to gas. This allows the head to cool down. Doing this will save you a world of greif with bend valves and head cracks. After you shut it down be sure the starting handle is back (in the diesel position) this keeps the starting valves seated and allows them to cool off.
I'm rambleing on here but if I can help .....yell

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PASteve

02-03-2004 16:22:35




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 Re: MD compression in reply to Ray , 02-03-2004 15:06:25  
The fact that there is so much variation in compression indicates a problem. 40 psig is definitely too low. I'm also assuming that these readings were taken with the lever set to run on gas. 120 psig should be more than enough to run on gas. I'm not sure what compression should be at cranking speed with the lever back. Keep in mind that the compression ratio changes when the lever is pulled back to run on diesel. When you pull the lever back and close the third valve (the one that exposes the spark plug), you're increasing the compression ratio. Compression values should be very different with the lever in different positions. As for the timing problem, the MD magneto turns the opposite direction of gas farmalls. I made that mistake once and had no idea what the problem was until I took the cap off and watched the rotor turn.
Be patient - they're great tractors
Best of luck

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