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The unofficial Mac 10-10 thread

bgelety

bgelety

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Bought an inexpensive 10-10a off Facebook marketplace as a quarantine project. Compression test when I got it home was about 60psi. I dismantled it and everything looked great, piston and the cylinder had the usual wear, no grooving. The ring end gap was .055. I found a set of 62814 rings on EBay and figured it was worth a shot since everything else looked good. I don’t have a bore gauge so I instead checked the new ring gap up and down the cylinder. It varied between .010 and .017. After reassembling, the compression is 75 psi and of course wont run more than occasionally idling. I think my choices are to bore this one to .020 over or try and locate something used with less wear? I’m not worried about recouping the money from the saw but instead the satisfaction of getting it together and running reliably. Thanks in advance for any suggestions.
 
PogoInTheWoods

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That end gap is on the edge of acceptable according to the 10 Series shop manual. The taper of the cylinder is also close to good if the measurements are fairly accurate, but a dial gauge is required for the best results for taper and out of round tolerances. The piston to cylinder wall clearance should also be checked to determine if the wear is excessive enough to consider over boring the cylinder. May also want to double check your compression testing setup for accuracy just to eliminate that as a possible variable. 75# seems awful low for new rings with the end gap you have unless something else is letting the compression by..., or out..., like a very loose plug or leaky decomp, though a 10--10A shouldn't have one. And another 10--10 is always a good idea!

end gap.jpg

p-c clearance.jpg
 
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Bought an inexpensive 10-10a off Facebook marketplace as a quarantine project. Compression test when I got it home was about 60psi. I dismantled it and everything looked great, piston and the cylinder had the usual wear, no grooving. The ring end gap was .055. I found a set of 62814 rings on EBay and figured it was worth a shot since everything else looked good. I don’t have a bore gauge so I instead checked the new ring gap up and down the cylinder. It varied between .010 and .017. After reassembling, the compression is 75 psi and of course wont run more than occasionally idling. I think my choices are to bore this one to .020 over or try and locate something used with less wear? I’m not worried about recouping the money from the saw but instead the satisfaction of getting it together and running reliably. Thanks in advance for any suggestions.
Compression that low with no obvious scoring? I might look for a spark plug thread repair thats letting the compression bleed out, the crank seals are shot .
 
bgelety

bgelety

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Bought an inexpensive 10-10a off Facebook marketplace as a quarantine project. Compression test when I got it home was about 60psi. I dismantled it and everything looked great, piston and the cylinder had the usual wear, no grooving. The ring end gap was .055. I found a set of 62814 rings on EBay and figured it was worth a shot since everything else looked good. I don’t have a bore gauge so I instead checked the new ring gap up and down the cylinder. It varied between .010 and .017. After reassembling, the compression is 75 psi and of course wont run more than occasionally idling. I think my choices are to bore this one to .020 over or try and locate something used with less wear? I’m not worried about recouping the money from the saw but instead the satisfaction of getting it together and running reliably. Thanks in advance for any suggestions.
That end gap is on the edge of acceptable according to the 10 Series shop manual. The taper of the cylinder is also close to good if the measurements are fairly accurate, but a dial gauge is required for the best results for taper and out of round tolerances. The piston to cylinder wall clearance should also be checked to determine if the wear is excessive enough to consider over boring the cylinder. May also want to double check your compression testing setup for accuracy just to eliminate that as a possible variable. 75# seems awful low for new rings with the end gap you have unless something else is letting the compression by..., or out..., like a very loose plug or leaky decomp, though a 10--10A shouldn't have one. And another 10--10 is always a good idea!

My compression tester is a SnapOn but its probably 30 years old (bought it new when I worked on cars in college). I just tried using just the screw in adapter and not the extension hose and it came up to 120psi. Better but not fantastic. I’ll pick up a new tester. It makes me wonder if the issue is fuel related. I did not rebuild the carburetor yet using a kit, I have had it apart numerous times and it looks as though it was just rebuilt recently so I cleaned it thoroughly and reinstalled. I can shoot fuel into the carb and get get it to idle but any attempt to give it throttle kills it. It’s then a bear to get to idle again and usually involves shooting additional fuel in. It has great spark but I have not messed with timing other than setting the point gap. I have a carb kit on order, maybe the pump or metering diaphragms are worse than I think? I thought maybe the air bleeder in the fuel tank was plugged but it blows clear.
 
bgelety

bgelety

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Compression that low with no obvious scoring? I might look for a spark plug thread repair thats letting the compression bleed out, the crank seals are shot .
I’ll check out the spark plug threads. I didn’t think the crank seals would affect compression? I think my compression gauge is part of the issue. I will pick up a new one and keep hunting.
 
bgelety

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After checking and double-checking everything else, I think I found my issue. It would run fine for a couple of seconds on an initial shot of fuel (and at one point even ran for a few minutes) but it was constantly starved for fuel. I was even to the point of installing the carb without the fuel pump cover plate to verify the pulse was making its way through the circuit. The diaphragm side always seemed to dry. I am assuming without the high-speed check valve, there could never be enough vacuum generated under the diaphragm to draw it down and allow fuel to flow? Now to figure out if I should fix it or try and find another carburetor (which could be missing it as well). I feel like I know the SDC carb inside and out now!
IMG_0149.jpeg
 
2broke2ride

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After checking and double-checking everything else, I think I found my issue. It would run fine for a couple of seconds on an initial shot of fuel (and at one point even ran for a few minutes) but it was constantly starved for fuel. I was even to the point of installing the carb without the fuel pump cover plate to verify the pulse was making its way through the circuit. The diaphragm side always seemed to dry. I am assuming without the high-speed check valve, there could never be enough vacuum generated under the diaphragm to draw it down and allow fuel to flow? Now to figure out if I should fix it or try and find another carburetor (which could be missing it as well). I feel like I know the SDC carb inside and out now!
View attachment 849447
The check valve kit is about $5 and readily available.

Sent from my SM-G950U using Tapatalk
 
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Jethro 2t sniffer

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Ben79

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Maintenance supervisor

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New arrivals today.

View attachment 852629

I read somewhere that this style flywheel cover was more common on saws shipped to Japan.

View attachment 852630

This one just appeared at the back door of the museum, my wife thought the guy was making a donation but I will find out for sure. Right now the level type compression release is stuck open.

View attachment 852631

Mark
Looks like a nice clean 7-10!
Definitely show the inside of that starter cover on the 10-10.
 
PogoInTheWoods

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Both look to be in wonderful condition.

Pretty easy for the uninitiated to get those decomps wrong putting them back together. Could also have the wrong length valve. Ask me how I know. LOL

I'd be interested in the 7-10 tag number if it still has one. Looks like an early one by the sticker. My infamous 7-10 is 10--10939 which puts it around '70~'71..., basically a left hand start 6-10A.
 
Jethro 2t sniffer

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Both look to be in wonderful condition.

Pretty easy for the uninitiated to get those decomps wrong putting them back together. Could also have the wrong length valve. Ask me how I know. LOL

I'd be interested in the 7-10 tag number if it still has one. Looks like an early one by the sticker. My infamous 7-10 is 10--10939 which puts it around '70~'71..., basically a left hand start 6-10A.

Have you ran that 7-10 much Poge?
 
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