Had hoped to avoid this like the plague.

[nccatfisher]

Thanks for the info, Pappy.

I thought about the oversized piston option, but evidently you can not bore out the 10 horse cylinders. It also appears from the manual that there are not and never have been oversized pistons for this motor. I am finding used standard sized pistons on eBay, but have no reason to believe they are any better condition then the ones I have. The cylinder bores mic out at exactly factory specs, but the current pistons are .002 over maximum piston-to-cylinder clearance so I would seriously consider boring if I could find the oversized parts.

Do you have a dial bore indicator so you can check for being out of round? That will give you a fit. I find it hard to believe rings could being so worn out and the bore wind up being ok.

 

[macawman]

No, I do not have a bore indicator. I used a digital inside micrometer and took multiple readings at 45 degree intervals. I'm thinking the rings were not that bad. They were all free. Additional, the first ring groove had the expected carbon accumulation. The second had relatively little and the 3rd groove had none at all. That leads me to believe the rings were doing a pretty fair job.

 

[nccatfisher]

No, I do not have a bore indicator. I used a digital inside micrometer and took multiple readings at 45 degree intervals. I'm thinking the rings were not that bad. They were all free. Additional, the first ring groove had the expected carbon accumulation. The second had relatively little and the 3rd groove had none at all. That leads me to believe the rings were doing a pretty fair job.

What was the end gap on them then? That should tell quite a bit of the story. If they were not stuck, not a great deal of carbon and the cylinders are within spec. you shouldn't have had such poor compression. There has to be an underlying problem somewhere or a combination of problems of components right at the edge of being right at out of spec to cause it to have such poor compression.

 

[Pappy]

Search should be on for NOS pistons then.
That was the main reason I asked about any looseness when the piston was on the down stroke. Now that you have the pistons out what does the wrist pin to bore fit look like? Should not be loose at all. Also, take a cylinder bore measurement on the "bridge" between the exhaust ports then above and below the ports. Curious to see if the material around the ports is bowed out a bit.

 

[macawman]

Nccatfisher, now that I have the motor torn down, I'm finding mostly gasket and seal issues. There are signs of real problems with both the head and crankcase cover gaskets. The lower crankcase seal is also cracked. It does appear now that some of the parts are at the edge of third tolerances, but I'm pretty sure gaskets are the main issue.

 

[macawman]

You got me on that one, Pappy. What are "NOS" pistons?

I think we are good on the wrist pins. There is no play whatsoever on them. I'll try to get those measurements today.

 

[nccatfisher]

You got me on that one, Pappy. What are "NOS" pistons?

I think we are good on the wrist pins. There is no play whatsoever on them. I'll try to get those measurements today.

NewOldStock

 

[macawman]

Thanks for the info, Nccatfisher.

Was hoping someone would tell me I'm full of crap about oversize bore and pistons are not available for this motor.

 

[Pappy]

Was hoping someone would tell me I'm full of crap about oversize bore and pistons are not available for this motor.

Okay, if you insist, you are full of guano! :beer:
There were indeed .020 oversized pistons available for that engine.
I just happen to know where two are. PM me and I will talk to you and give you details of where to have the block bored and who and where to get the pistons from.
Am assuming there are rings with the pistons.

 

[macawman]

Fantastic! Sometimes times I don't mind at all being proven full of it. Will pm you for details.

 

[macawman]

Thanks, Pappy.

 

[Pappy]

Thanks, Pappy.

You are more than welcome! When you make the trip to get the pistons I think you will be glad you did.

 

[macawman]

The exhaust tube loading assembly tubes are supposed to be a straight through shot, right? No baffles or such?

 

[Pappy]

Exhaust tube loading assemblies? What is this part of which you speak?? :roll:
The exhaust tube is normally a straight through style if that is what you are asking.
I understand the search is still on for pistons?

 

[macawman]

That should be exhaust loading tubes assembly. Both tubes are completely or near completely plugged up with carbon. It's packed solid and you can't see daylight thru either tube. They will have to be drilled out before I can do any serious cleaning, but want to make sure there is nothing inside the tubes that drilling would mess up.

 

[macawman]

It appears to be something similar in function to the upper air Silencer and loading tube assembly on the carb. Moog point now since I went ahead and drilled out the tubes last night. Got it cleaned out, but my .45 call bore brush is toast. Guess I will be going by Larry's today.

 

[nccatfisher]

It appears to be something similar in function to the upper air Silencer and loading tube assembly on the carb. Moog point now since I went ahead and drilled out the tubes last night. Got it cleaned out, but my .45 call bore brush is toast. Guess I will be going by Larry's today.

That may have played a big part in it not running well along with the poor compression. It may have even ran a little longer like it was without the exhaust restrictions.

 

[macawman]

I'm wondering the same thing. Those tubes being plugged up would be the equivalent of the old "tater up the tail pipe" trick.

Question. If a new piston rings is squared up in the cylinder and the end gap is equal to the manufacturer's minimum gap, what does that say about the cylinder?

 

[nccatfisher]

I'm wondering the same thing. Those tubes being plugged up would be the equivalent of the old "tater up the tail pipe" trick.

Question. If a new piston rings is squared up in the cylinder and the end gap is equal to the manufacturer's minimum gap, what does that say about the cylinder?

Well, if your measurements I remember are all correct I believe you would be good to go.

I remember asking if you had a dial bore indicator and you said no, but how did you check for out of roundness?

I do remember that your pistons were out of spec. Also, you will have to deglaze those walls, you need to be measuring after you do that to get a good final number if you are planning on rebuilding back stock bore.

I am no expert but it the bore is in specs. I see no reason why not. BUT, I am no expert on these old motors. Pappy may know something or some reason they didn't do well without boring.

 

[macawman]

I measured the cylinders at 45 degree intervals around the cylinder and at 5 or 6 locations up and down the cylinder. Premitive, I know but the best I have at hand. I feel pretty good about the cylinders, but the pistons are another matter. The cylinder could be good, but the piston worn out because one is steel an the other is aluminum.

Given that the rods, bearings, pins and pistons all have to be changed whether the pistons standard or over sized, the single answer to all the questions is to bore it and be done with it.

Maybe I should see if I can find a machine shop that will measure the block and pistons for me.