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persof

Automatic Compression Release

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persof

I have a 312-8 that is having increasing problems starting. You turn the key, the engine goes

about a 1/2 turn and stops with the starter making a whine like something is bound up. I have

replaced the starter in the past with minimal results.

I am now thinking that this is may be a problem with the automatic compression release; do you

agree, how hard is the camshaft/ACR mechanism to replace?

Thanks

Francis

Middletown, MD

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TT

If you have ruled out all other potential electrical problems, (battery, cables, solenoid, etc.) try adjusting the valves. While the breather is removed, you can watch for proper function of the ACR. The exhaust tappet & valve should lift slightly during the compression stroke.

Early versions of these engines did not have ACR and could still be pull-started. Although the ACR system does make them turn over more easily, a good gear-drive starter shouldn't have a problem - even if the ACR isn't working.

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Save Old Iron

Wiring can be eliminated by measuring the DC voltage drop (power lost) from the battery (+) terminal to the starter terminal. Place a meter probe on the battery (+) and the other probe on the starter terminal. Crank the engine and watch the multimeter. If the meter registers more than 0.5 volts - wiring could be a contributor to your problem.

p.s. the voltmeter reading will fluctuate as the starter draws more and less current thru the 4 cycles of combustion - an analog meter (one with a pointer) may be a better choice over a digital meter - unless the digital has a max / min feature to record the maximum voltage drop during the testing period.

click images to enlarge

startfunctionvoltagedropok_zps1525a383.gif

startfunctionvoltagedropbad_zps45635265.gif

an alternate method would be to connect the starter directly to another lead acid battery or charger via jumper cables.

6411c88c.gif

If the starter cranks over the engine without stalling, this would also confirm the start circuit wiring is in need of further inspection.

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rmaynard

I don't think that your starter would whine if the there was too much compression. It would just stop. A whining noise usually comes from the bendix mechanism/gear not engaging with the flywheel. I would remove the starter, clean the bendix assembly to make sure that it is moving smoothly. Then reinstall the starter making sure that it is properly aligned. I have never had to use shims under the mount, but have heard of others doing so to achieve better alignment..

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squonk

I'm thinkin he's not carrying enough amps to get the starter working right. Battery itself, cables connections, solenoid ect. I bet it's in there. My C-160 did the same thing when i got it. The positive cable connection at the solenoid stud for the solenoid to starter cable became loose. Crimped it down,problem went away, then I bought a new cable.

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persof

When bought this tractor a couple of years ago I disconnected and cleaned until shiny "all" electrical connections to resolve a no start condition. The tractor is stored under cover. The next year I removed all switches and interlocks.

I will use the VOM to review the electrical systems. Seems to me that if the automatic compression release is working correctly then I should be able to turn the engine over by hand.

Thanks

Francis

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Save Old Iron

Seems to me that if the automatic compression release is working correctly then I should be able to turn the engine over by hand.

agreed - you should be able to "slide" the engine thru the compression cycle by hand. If you can not - remove the spark plug and try it again. If it's ACR, the engine will now crank or rotate by hand easily thru the compression cycle.

Cleaning the terminals on the wiring is certainly a good place to start. One issue with terminal corrosion is that is also present at the point where the wire is crimped inside the terminal. An as has been mentioned before, the corrosion that eats thru several strands of the starter wiring could actually be up inside the insulation of the cable - an inch or so up from the terminal itself.

Many brands of wiring on the market do not prevent oxygen from leaching thru the wiring insulation and attacking the copper strands underneath. I can tell you I have cut wires back 10 - 12 inches from terminals looking for "clean copper" and still end up with heavily oxidized strands.

The voltage drop test will tell the story. I do have to add more detail to the pics tho. The meter clips should be connected DIRECTLY TO THE (+) BATTERY LUG - NOT THE WIRE TERMINAL. With the meter (+) clip on the battery lug and the (-) meter lead DIRECTLY ON THE STARTER LUG, you will get a true indication of voltage drop across any and all mating surfaces of the starter wiring - external and internal to the wiring and terminals.

Good luck.676fe03e.gif

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persof

A new cable is not expensive or difficult; I will replace both and try to spin by hand.

Thanks

Francis

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rmaynard

Save your money and get out your jumper cables. A direct connect from battery to starter will answer a lot of questions.

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tunahead72

676fe03e.gif

What the heck is this?? I thought I had a dang fly on my screen!

676fe03e.gif

Oh crap, there's another one! :icecream:

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JackC

Here is a Video on how valve adjustment can cause hard starting on an OHV engines.

Remove plugs and if starter spins engine, suspect valve adjustment.

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markjs

An MTD? :scared-eek:

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persof

to do on this saturday!

Thanks

ps..the Kohler manual mentioned this and I did not believe it could make that much difference

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persof

I started to open things and it looks like I can get a partial view of the ACR mechanism. What should I be looking for?

camgear.jpg

Thanks

Francis

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rmaynard

That little hair spring that you are looking at keeps those arms from swinging out until the engine is running at approximately 600 rpm. As pictured, the ACR looks fine.

post-2221-0-75938400-1349572368_thumb.jp

Edited by rmaynard

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persof

Today I set the valve lash per the Kohler manual and found some hard plastic bits wedged in between the ACR parts?? There were some larger bits that looked chewed up near by. These things were discovered this morning when I had time to examine things more carefully. I'll report soon as I have time.

Thanks

Francis

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Save Old Iron

were the valve clearances far out of tolerance?

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persof

The intake was a tiny bit loose and the exhaust was to tight. Where do you suppose those plastic bits came from? They were a light green and some small crumbs had wedged inbetween the ACR parts.

Thanks

Francis

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Buckshot 1

:) Francis, the only plastic peice inside of a K-series should be the governor gear. Unless someone had it apart before and tried some funny tricks. Other than that I have no idea. :flags-usa:

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persof

Remember I said that per the Kohler manual the exhaust tappet was "tight", well I started the engine and it started just fine but there was a lot of tapping going on????

Look at the scanned in page that says .018" for the exhaust tappet; do I need stronger glasses, is it a misprint or does some one know the correct setting?

post-2413-0-73855400-1349734889_thumb.jp

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rmaynard

Francis,

.018 is the correct cold setting. I would go back and check the settings again if you think you may have set it wrong.

As far as the plastic wedged in the ACR, that is a mystery.

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JackC

Brian MIller's Website tells you all you need to know about valves and then some.

He says:

Use steel feeler gauges to set the valve clearances. For the 10-16hp engines, for ordinary yard use, the valve clearances are: .008"-.010" for the intake and .017"-.019" for the exhaust with the piston at TDC on the compression stroke. This is when both valves are fully closed. For competitive pulling, set the valve clearances at .010" for the intake and .014" for the exhaust.

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persof

I was thinking,woulden't the ACR be holding the exhaust valve open when the piston isat TDC on the compression stroke?

If yes then the tapping is my fault so maybe adjustments should not be at tdc?

thanks

Francis

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rmaynard

At TDC (compression stroke) the valves are both fully closed and the ACR is not engaged.

Read the section in your manual on ACR. The manual explains how it works and at what point in the compression stroke the ACR releases the pressure.

Edited by rmaynard

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Save Old Iron

The plastic material in the acr could be from a broken oil level sensor (if the engine ever had one installed on this pan or another pan).

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