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Discussion Starter · #21 ·
Those shiny warped spots are 'Hot Spots' right in an area common with clogged cooling fins that usually cause that in those areas where the shiny spots are in the cylinder.
Correct, right above that is the intake tube where a sweet nest made of insulation was.

Then you figure how old that engine is and how long it was run with the clogged cooling fins to cause that. That mower was popular 40 plus years ago. That unit could be going on close to 50 years in age by now, I have a couple of them from new. They just sit in the garage now.
Yep, 1968 so 53 years old.

That engine used the camshaft driven PTO to drive the wheels. They haven't been produced in decades plus being the 'L' head engine, you can tell it is old and getting new parts for them will not be that easy due to its age.
I rebuilt one 15 years ago, the parts were hard to get then. I ran it for a few years and when it died, I just left it sit and let one of my older Honda's take its place.
I have a pdf of the IPL for this engine, almost every part you can look up on eBay and someone has a bunch of NOS they're trying to offload relatively cheaply. There's even a few bronze gears for the pto shaft out there.

They did have excellent traction for the steep hills I have, that's why I liked it.
The old Hahn Eclipse mowers were tied in with Gravely back in the 60's and early 70's, Gravely dealerships used to sell them.
The Hahn Eclipse mowers I have, have the Gravely name stamped on them with the Hahn name.
They were a good tough mower that were built to last and take a lot of abuse.
That's awesome. Now I'm really glad I nabbed this up. Maybe I'll go ahead and do a full resto on it.
 

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Discussion Starter · #22 ·
Well jeez I think maybe a large reason for the loss of compression might have been the head gasket surfaces being warped too:

Automotive tire Rim Automotive engine gasket Motor vehicle Auto part


Motor vehicle Automotive tire Automotive design Automotive engine gasket Rim


Motor vehicle Automotive tire Automotive engine gasket Bicycle part Audio equipment


Motor vehicle Automotive engine gasket Gas Audio equipment Electrical wiring


Shoe Table Automotive tire Circular saw Wood




And I've got the low spots in the cylinder down to this, after checking with a bore gauge I'm gonna do a final finish hone to 320g with a ball hone.

Helmet Rim Bicycle part Bumper Composite material
 

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Discussion Starter · #23 ·
Alright this is probably not the right way to record this information but I'm pretty sure I've got what I need. So what I did was set my dial bore gauge to .010" over, which is 2.5715". Then I measured at 6 points as depicted in my super accurate drawing here. And because every measurement was under the setting, I should only need to go to .010" over.

Handwriting Rectangle Gesture Font Parallel


All these numbers are negative so 2.5715 minus whatever the number is to get the actual measurement. As expected we are out of round by .0015", the manual I have says up to .0025" out of round is acceptable for aluminum cylinders. And of course I've got quite a taper going on in the one direction, and reverse egg shape in the other. Not that I'm going to be able to avoid having to visit a machine shop but at least it won't require going .020" over.
 

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Discussion Starter · #25 ·
Parts are starting to roll in for this thing. And I bought a rigid hone that I'm gonna try to set up on a drill press. I'll have to slow it way down probably but it's worth a shot. I hate waiting on machine shops who always have more important jobs to do.
 

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Discussion Starter · #27 ·
I'll be dipped. It's just like it. Pretty much. It didn't seem to matter what search terms I used I couldn't find one like it on an image search. Must have been missing Allis Chalmers. Too cool
 

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Discussion Starter · #28 ·
Tonight I had a chance to play with this thing:
Hand tool Wood Tool Metalworking hand tool Air gun


You still have to be careful and check often, and try to concentrate the honing on the area that needs it. But here are the new numbers, quite a bit more consistent than before. I think I'll take it the rest of the way with the ball hone:
Handwriting Rectangle Wood Font Material property



And I'm just following the manual which says to just punch it out exactly .010" over the std bore measurement rather than giving an actual piston to cylinder clearance spec. Though there's a range on that so I'm just going with the smaller number. And when I subtract the new piston skirt measurement from that I get .0045" so I guess that sounds right.
 

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Discussion Starter · #29 ·
Well I suspect the micrometers I bought off eBay need calibrated and I don't have any standards. I know I could just order some and wait yet another few days for something else to come in to continue building this engine.

...or

I could just lock the 2-3" mic on the setting for the piston -whatever it is- and then just use the dial bore gauge (which I believe to be very accurate, or at least very consistent) to final hone the cylinder out to final clearance spec. The only problem with this is this idiotic refusal on Briggs' part to post what that spec is. This is stupid in my opinion because by just telling you to punch it out exactly 10, 20 or 30 over they're essentially telling you what the clearance should be. If you have accurate mics that is. They won't even publish what the std piston is supposed to measure, if they did then I could just figure out the factory cyl wall clearance and just make sure my cyl is that amount bigger than the piston using the dial bore gauge.

Moreover, there's a range of one thou for the std bore. So how do you bore it out "exactly" .010 over? What if you get it 10 over the lower amount and the clearance is .0025"? What is different about Briggs engines that makes it so important to be secretive about cyl wall clearance but rather explicitly state to bore it out exactly 10 over? It seems so stupid because isn't that what boring 10 over means?

I guess now that I'm done ranting, what clearance should I go with?
 

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Discussion Starter · #30 ·
Here are my current numbers according to the diagram I posted pictures of above, only this time these are actual piston to cyl wall clearances that I arrived at using the method in the previous post.

AB
.0035".003"
.0035".0035"
.0035".0035"

Which I think is amazingly good compared to how it started. I'm tempted to just start filing rings and cleaning this thing up for final assembly, but instead I'm going to wait on the set of standards I ordered and make sure my cylinder is exactly .010" over the factory spec.
 

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Discussion Starter · #31 ·
So as I explained here, I unknowingly bought a bare aluminum piston and this application requires a chrome plated piston:

Ultimately I decided that it's not worth destroying this engine and prolonging this process over 30$, so I ordered an NOS Briggs and Stratton 10 over piston that I can be certain has the proper coating. By the time it gets here I will have acquired a set of standards and will have my mics calibrated, then I'll finally be ready to go forward with this.
 
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