K181 ACR Questions

[adsm08 3,237]

I have questions about the automatic compression release on the K181s.

 

Background:

I blew up the 181 in my 855 last weekend. I am in the process of rebuilding it, but I would like the tractor up and running in the mean time. I had a spare 181 from a 66 JD 110 in the garage so I got busy with the activities listed in my signature line. I am at the "sometimes they work when I am done" portion, but this is not one of those times.

 

The engine that threw the rod has the two-piece cam with the ignition retard flyweights, and not the ACR style, despite coming out of a 65 tractor. The engine I just put inside is definitely the ACR cam. One of the piece I had to swap over to make it fit was the oil pan, so I have personally and visually inspected both camshafts.

 

Now I have the JD long block with the ACR installed in the 855 chassis. I have the complete wiring, ignition system, and fuel system from the WH installed. The WH engine ran right up until the rod broke, I was running it and getting the oil warm to change it when it let loose.

 

The engine will not start. I do not know for sure that it ran before, or when the last time it did run was. It cranks, I can smell fuel and it cranks like it has no compression. I don't have the muffler on yet, so I can see right into the block and I know the exhaust valve is not moving.

 

I can also remove the spark plug, put a light up to the exhaust port, and see that the valve is open, and seems to be open quite a bit.

 

I know almost nothing about these ACRs except that they modify the exhaust valve timing at cranking speed, and hold the valve open. I don't know how much or how long though.

 

So the question is, how do I tell the difference between a working ACR and a stuck valve? Is there anything useful that can be seen by removing the valve cover?

 

I have not ruled out an ignition issue as I seem to be lacking spark (if everything was working except the valve hanging open I'd expect it to be shooting flames out the exhaust port), but I am concerned about the lack of movement from the exhaust valve as well.

Edited December 19, 2020 by adsm08

[adsm08 3,237]

After reading through this article here I think one of my flyweight springs may be off the weight.

 

http://gardentractorpullingtips.com/valvecam.htm

 

I remember briefly seeing the spring as I was spinning the engine by hand to inspect stuff, but not paying much attention to it. After seeing some of these pictures I think it may not have been hooked on correctly. Possibly disturbed while I tried to pull a wad of some sort of fabric or fiber off the spring.

 

I'm still not sure how to tell the difference between a functional ACR and a stuck valve.

Edited December 19, 2020 by adsm08

[oldredrider 2,553]

Pull the head off. With the intake valve up, try tapping the exhaust valve down. Roll the engine over and see if the ex valve opens and closes. If it does, a sticking valve is your problem. 

[stevasaurus 23,277]

I think the 2 piece cam is for the K-161.  The spring with the single cam is made to open the exhaust valve a little to relieve compression when either cranking the starter or pulling the starter rope.  Once the engine starts, the ACR does nothing and you have full compression.  If you have the head off and you turn the engine over, you should see the exhaust valve hang open a "little" on the compression stroke.  Once you have RPM's, the spring does not keep the exhaust valve open any more.

   If your spring is broke, then you do not have ACR...your engine will still start and run...just harder to pull or crank.  If you had a 65 hsp outboard, you may feel the difference.  Actually, I think that 2 piece cam shaft used a different system...prior to ACR.  Are you sure you do not have a 7hsp Kohler??

 

 

 

[adsm08 3,237]

13 minutes ago, stevasaurus said:

I think the 2 piece cam is for the K-161.  The spring with the single cam is made to open the exhaust valve a little to relieve compression when either cranking the starter or pulling the starter rope.  Once the engine starts, the ACR does nothing and you have full compression.  If you have the head off and you turn the engine over, you should see the exhaust valve hang open a "little" on the compression stroke.  Once you have RPM's, the spring does not keep the exhaust valve open any more.

   If your spring is broke, then you do not have ACR...your engine will still start and run...just harder to pull or crank.  If you had a 65 hsp outboard, you may feel the difference.  Actually, I think that 2 piece cam shaft used a different system...prior to ACR.  Are you sure you do not have a 7hsp Kohler??

 

 

 

 

 

I'm sure it isn't a 7 hp.

 

The early K181s used an ignition retard system that operated similar to the ACR system but it adjusted the ignition timing to fire it off at or just after TDC. Both the engines have the info tags intact enough for me to be able to read the engine designation as K181S.

 

I really didn't want to have to pull this head too. I know it isn't hard, I just didn't want to do it.

[pfrederi 18,669]

You can watch the exhaust valve in the valve spring chamber.  As Steveauraus said you will see it bump up a bit during the compression stroke if your ACR is working

[adsm08 3,237]

1 hour ago, pfrederi said:

You can watch the exhaust valve in the valve spring chamber.  As Steveauraus said you will see it bump up a bit during the compression stroke if your ACR is working

 

Then there is no doubt the valve is stuck open. I held a light to the exhaust port and hit the starter. The valve never closed.

[oilwell1415 563]

The valve is stuck open.  Even if the ACR failed completely the valve would still open and close normally, the ACR just retards the cam at low rpm to ease cranking.

[adsm08 3,237]

Yup. The valve was stuck. I suspect that the last time the engine was run, or cranked it stopped with the valve open and then stayed that way for many years.

 

I worked it around by hand a few times with the head off, and it stayed up each time. Then I gave it a good shot of PB into the exhaust port and worked it by hand twice more. Valve is now moving freely. Fortunately I already had a head gasket for this thing on my shelf, so I'll get the head and block cleaned tonight, bring my torque wrench home from work tomorrow, and hopefully in 24 hours I'll have a running tractor again.

 

I was also able to get the spark issue sorted out. Turns out the points were not in good shape, again probably from sitting. I installed the points from the engine that blew up since they were replaced this summer. I'll kind of got a little redneck engineering into setting them since I can't find my feeler gauges. I figure the average thickness of a piece of paper is .0039". The setting on the points is .018-.022". .020/.0039=5.12. That means 5 pieces of paper stuck in there should get you close enough to run. I'll bring my good feelers home from work tomorrow and set them properly before trying to start it, but I think that would have worked well enough in a pinch.

[RandyLittrell 3,903]

On 12/19/2020 at 4:58 PM, adsm08 said:

 

I'm sure it isn't a 7 hp.

 

Both the engines have the info tags intact enough for me to be able to read the engine designation as K181S.

 

 

 

A lot of things happen to little tractors in 50 years, you really can't be for sure unless you measure the piston. Someone could have put a different block in it and reused the tin. 

 

 

 

 

Randy