1999 312-8 compression relief valve question

[608KEB 794]

I'm looking at my Dad's 99 312-8 for some reason the compression valve is sticking. I have to remove the spark plug to release the pressure. Then it will start. Where is the compression valve on this tractor? I know very little about a OHV motor. 

[WHX?? 46,673]

I would start by popping off the valve cover and checking the tappet clearances. Should be done every so often anyway. Specs should be in the manual. Not an expert on this motor but  I don't think there is a comp. release on these.

I do know a fine looking  when I see one tho!

I would love to put one of those engines in a 520 chassis.

[gwest_ca-(File Mod) 10,478]

Garry

[608KEB 794]

Ok, I'll look into it. I'll report back with my findings.

[608KEB 794]

22 hours ago, WHX21 said:

I would start by popping off the valve cover and checking the tappet clearances. Should be done every so often anyway. Specs should be in the manual. Not an expert on this motor but  I don't think there is a comp. release on these.

I do know a fine looking  when I see one tho!

I would love to put one of those engines in a 520 chassis.

You'd  put one of those Kohler Command engines in a 520-H chassis? I had to pick the 312-8 up in Gailon Ohio. About a year ago. Low hour machine. But a few minor issues now. My Dad is 82. He can fix things. But this was a little  beyond what he could do.

[608KEB 794]

I have the valve cover off. What's next? Remove the rocker arms that are on top of the valves? I downloaded the engine manual. Intake should be set at .0030. Exhaust should be set at .0035. I'm assuming the exhaust valve is the one near the muffler.

Edited December 9, 2018 by 608KEB

[lynnmor 6,762]

Apparently you have hydraulic lifters, no adjustment is required.

[608KEB 794]

34 minutes ago, lynnmor said:

Apparently you have hydraulic lifters, no adjustment is required.

How would I fix the problem  of having to remove the spark plug to relieve the pressure built up in cylinder?  It will start after doing this.

[Digger 66 3,476]

6 hours ago, 608KEB said:

How would I fix the problem  of having to remove the spark plug to relieve the pressure built up in cylinder?  It will start after doing this.

 

Why would want or need to relieve cylinder pressure ?

Every internal combustion engine needs sufficient cylinder pressure to operate .

I'm no expert on this particular engine but...

If the engine is equipped with a decompressor , this is usually achieved by ( some mechanical actuator ) holding the exhaust valve slightly off the seat just before the spark-plug is going to fire .

If this engine is not so equipped then either your starting system is weak , your valve timing is off , or spark is occurring before it should .

[Tuneup 1,416]

That's likely the key. Battery, cabling, solenoid or starter weak and can't get past the compression without momentum through the next cycle. Start with the battery - make sure it's load tested and ready to go. I would jumper it to a car battery as a VERY QUICK test to see if it overcomes the compression. Don't leave it connected any longer than necessary. That'l give you a quick answer on the battery's fitness.

[rmaynard 14,860]

According to the manual provided above, in section 10 (10.1), this engine is equipped with ACR. Here is a quote from the manual:

 

Automatic Compression Release (ACR)
This engine is equipped with an Automatic
Compression Release (ACR) mechanism. ACR lowers
compression at cranking speeds to make starting
easier.

Operation:
The ACR mechanism consists of a lever and control
pin assembly attached to the gear on the camshaft. At
cranking speeds (700 RPM or lower), the control pin
protrudes above the exhaust cam lobe. This pushes the
exhaust valve off its seat during the first part of the
compression stroke. The reduced compression results
in an effective compression ratio during cranking of
about 2:1.

 

So rather than hazarding a guess to your original question about ACR, I simply looked it up in the manual. Good luck with your problem.

 

[608KEB 794]

Thanks guys for the inputs. I'll check these things out today. I'll report my findings. 

Edited December 9, 2018 by 608KEB

[rmaynard 14,860]

Before going to a lot of trouble, just test the ACR. Since you have the valve cover off and can see the valve stems & rockers, rotate the engine until it is about to enter the compression stroke. You will notice that the exhaust valve will open and close slightly as the compression stroke begins. If it doesn't, then you can safely assume that there is something amiss with the ACR.

[608KEB 794]

On 12/9/2018 at 7:20 AM, rmaynard said:

Before going to a lot of trouble, just test the ACR. Since you have the valve cover off and can see the valve stems & rockers, rotate the engine until it is about to enter the compression stroke. You will notice that the exhaust valve will open and close slightly as the compression stroke begins. If it doesn't, then you can safely assume that there is something amiss with the ACR.

It looks like the exhaust valve is moving fully up and down. If the ACR is not working. Does this mean I have to disassemble  the engine? Silly question, but thats what it looks like.

Edited December 11, 2018 by 608KEB

[rmaynard 14,860]

The exhaust valve should move fully up and down on the exhaust stroke. However, we are talking about only the compression stroke where it should open and close just slightly at the beginning of the stroke. Yes, the engine will have to be at least partially disassembled to repair an ACR.

[608KEB 794]

32 minutes ago, rmaynard said:

The exhaust valve should move fully up and down on the exhaust stroke. However, we are talking about only the compression stroke where it should open and close just slightly at the beginning of the stroke. Yes, the engine will have to be at least partially disassembled to repair an ACR.

I'll check it out.

Edited December 9, 2018 by 608KEB

[rmaynard 14,860]

1 minute ago, 608KEB said:

I apologise for my lack of knowledge. Where should I look? The intake valve?

 

Exhaust valve. 

 

What you have is a 4-stroke engine. Every complete revolution is a "stroke". First stroke is intake. Intake valve opens, exhaust valve is closed, the piston goes down and gas/air mix is pulled in. Next stroke is compression. Both intake and exhaust valves are fully closed and the piston starts moving up compressing the gas/air mix. If you have an ACR, this stroke is where the exhaust valve opens slightly at the beginning of the stroke, then closes quickly as the piston goes up, compressing the mix. Third stroke is where the spark ignites the fuel/air mix and forces the piston back down. Fourth stroke is exhaust where the exhaust valve opens and the rising piston forces the burned exhaust gases out. Then the cycle starts all over again. As soon as the engine reaches between 600-700 rpm, the ACR mechanism disengages, full compression is realized, and the engine runs.

[lynnmor 6,762]

13 minutes ago, rmaynard said:

 

Exhaust valve. 

 

What you have is a 4-stroke engine. Every complete revolution is a "stroke".

I know that you understand the way things work, but you made an error when you said "complete revolution."  Just so folks understand, there are two strokes for each revolution as the piston goes down and then back up.  Down is one stroke and up the other.

[rmaynard 14,860]

You are correct. 

[608KEB 794]

So, I went on Google and YouTube.  I read up on these motors. I would rather have a K series  or Onan motor! Seems like these motors are problematic. 

[608KEB 794]

10 hours ago, rmaynard said:

The exhaust valve should move fully up and down on the exhaust stroke. However, we are talking about only the compression stroke where it should open and close just slightly at the beginning of the stroke. Yes, the engine will have to be at least partially disassembled to repair an ACR.

The ACR is not working. I will have to take motor apart to get to it.