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Old 04-14-2019, 11:21 PM
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Location: MI
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Originally Posted by rsshallop View Post
Hello, My progress on rebuilding the K241 for my cub 108 is coming along at full turtle speed. Well, At least there is some progress. And, this is one of the first posts I have made since joining this website that isn't a shout out for help. So, I feel good about that. After cleaning the valve guide on the exhaust side both guides appear to be withing usable specs (measured with a mic).

Exhaust guide: mid-point between .312 and .313
Intake guide: mid-point between .312 and .313

(ol'George, you were right. The reamer did clean up a considerable amount of carbon. I'm sorry I didn't that a picture of the carbon on the end of the reamer to document)

Next is the cylinder bore (taken several times with my mic and telescoping gauge)

A axis top center and bottom: 3.252, 3.251, 3.251
B axis top center and bottom: 3.253, 3.252, 3.252

(I'm pretty sure that these measurements fall will within the max wear limit 3.2545, max out of round .005 and max allowable taper .0015)

Next, the crankpin. These measurements were very difficult to take

A axis left middle and right: mid-point between 1.50 and 1.499
B axis left middle and right: mid-point between 1.50 and 1.499

( I think I will be OK here too with a max out of round of .0005 and a max taper of .001)

Next, camshaft end play: .013 (taken with a feeler gauge)

******************

Using these measurements I plan to take the block to someone in town that I met who does small engine repairs. He has some hand tools to hone the cylinder wall with a new cross hatch and cut the valve seat to 45 degree angle. Then, I will re-measure the cylinder bore to see if it is still within specs. If all is good, I will the order new parts to put it back together.

- new exhaust and intake valves
- new STD piston, rings and connecting rod.
- shim kit for camshaft end play
- new governor gear

Also, the pully/PTO end of the crankshaft needs a new key path cut into it. I will have to have that done at a machine shop.

Hope this posting finds everyone well,

Ross
Check that the crankshaft, where the keyway is wallowed out, that it is not worn undersize,
if not, then put the new keyway *90 to the old one.

Just use a dingle-berry/ ball hone to de-glaze the bore for new rings.
You don't want to remove any material, making an already worn bore larger.

When measuring the crank, the most worn part is where the piston is at the top of the stroke, and the least, 1/2 way down, (*90) that is your comparison to be read.
Also check in the same position to see if the crank pin is tapered about it's length, in-other-words on the surface that would see if the rod was rocking side to side, causing a taper on the crankpin.
In an ideal situation, the crankpin would show no wear or taper.
An out of round crankpin will knock during usage as will a worn pin.

Your combined cyl taper is .002 top to bottom max.
It will work, but it will use just a tad of oil as the piston rings will be expanding/contracting as they go up/down and you have an out of round condition where the wall contact will be lost.
---- But oil usage will use less than it does now.
The right way would be to bore/hone to first oversize, but an economical fix is re ring as you plan.
Don't know how long you plan on keeping it or how many hours you are going to use it.
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