K241 Cams

[WHX?? 46,774]

In a recent rebuild of a 241 10hp I noticed the cam did not have the ACR cam but did have the spark advance on it.  Pics one and two. 

A second 241 that was off the same year same model tractor (1055's) did have the ACR cam. Pics three and four. 

My thought is Kohler changed the cam they used sometime in '65? It doesn't appear that a PO has been in either motor but only God and a PO knows that fer sure!

I used the spark advance cam in my rebuild but had I known I had the ACR cam I might have used that one instead.

Question is what would have been the better cam to use and why did Kohler switch from one to the other?

[ebinmaine 63,137]

6 minutes ago, WHX22 said:

 

Question is what would have been the better cam to use 

I'm gonna follow along...

I'm not super familiar with these smaller engines internals.

25-30 years back I messed with a V8 or two and I have a decent understanding of how they work but no hands on experience with Kohler...

 

[WHX?? 46,774]

I thought I knew these motors like the back of my hand too but always get thrown a curve ball. 

[Achto 26,556]

Curious Jim. I Knew the '61 k161 in the  701 did not have ACR, I thought all the rest of with K models had it.  Just wondering, did both engines have the same spec number? Is there a possibility that a PO installed a short block at one time?

[oldredrider 2,547]

I'm going to guess Kohler changed the cams to provide easier starting. The ACR says it: compression release. 

Try yank starting  a big block without it and you'll appreciate the ACR.

I rebuilt a K141 that had the spark advance cam for a friend. After the rebuild his wife couldn't start it because of the compression, and it was her tractor.

Edited April 20, 2019 by oldredrider

[WHX?? 46,774]

Hard to tell the motor that had the spark advance cam had no name plate. The motor with the ACR does have a name plate which I borrowed for the build motor.

I was under the same thoughts as the 701 being the only one without ACR. In a service manual for the 241 it does mention the spark advance cam and it is also shown on a parts manual for the 241. This motor is electric S/G start. I also noted that the intake valve is ever so slightly open when the piston starts it compression stroke.

[953 nut 51,682]

13 minutes ago, WHX22 said:

the intake valve is ever so slightly open when the piston starts it compression stroke.

I had always thought that this is common to most cam designs, air/fuel mixture is flowing in while the piston is changing direction at BDC. I would think the ACR cam was an improvement that seems to have stood the test of time. Like @oldredrider pointed out, makes it easier to start.

[ebinmaine 63,137]

1 hour ago, 953 nut said:

this is common to most cam designs, air/fuel mixture is flowing in while the piston is changing direction at BDC

This is true for most 4 stroke engines.

The valves are open longer than a full up or down movement.

They are opened as early and shut as late as possible for maximum efficiency.

It also helps intake flow, increases scavenging of the exhaust to help there as well.

Pushing air/fuel back out of the carb is obviously a problem so there's a fine line drawn there.

On the other side though, many engines keep the exhaust valve and intake valve open simultaneously around TDC between exhaust/intake strokes. It's been shown to help draw the mix in through the carb faster if the intake valve is opened while the exhaust gasses are still leaving. Scavenging effect.

 

 

[WHX?? 46,774]

Thanks for the schooling fellas. To add further confusion manual says there are timing marks on the cam. I triple checked this when assembling and found no such marks.