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Cracftsman 3.7 parts and questions....

dangerousatom

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Just ripped into my friends fathers old Craftsman 3.7/18 as it seems to have given up the ghost a few years ago. After getting a general comp on it 130-140 it loses psi in 2-3 seconds. I can hear it hiss out somewhere, Im assuming the crank oil seals. The piston and jug look to be in good shape, minimal visible lines no scratches at all. All the bearings are in great shape, with zero build up in the crank housing or even on the pistons underside. No cracks or visible leaks in the body seal after being split either.

After poking around on here and other online info areas it seams parts are few, but the seals are available along with the bronze thrust bushings ( would love to toss a new piston-crank in it ) My question is do the crank oil seal hold compresion? The seals seem awful spindly compared to the 340 husky I just redid . I dont mind spending a few bucks on seals n bushings if thats all it is???

Bronze Bushings = Poulan 530015354
Seal = 19097
 

countryhog

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Just ripped into my friends fathers old Craftsman 3.7/18 as it seems to have given up the ghost a few years ago. After getting a general comp on it 130-140 it loses psi in 2-3 seconds. I can hear it hiss out somewhere, Im assuming the crank oil seals. The piston and jug look to be in good shape, minimal visible lines no scratches at all. All the bearings are in great shape, with zero build up in the crank housing or even on the pistons underside. No cracks or visible leaks in the body seal after being split either.

After poking around on here and other online info areas it seams parts are few, but the seals are available along with the bronze thrust bushings ( would love to toss a new piston-crank in it ) My question is do the crank oil seal hold compresion? The seals seem awful spindly compared to the 340 husky I just redid . I dont mind spending a few bucks on seals n bushings if thats all it is???

Bronze Bushings = Poulan 530015354
Seal = 19097
Yes
 

dangerousatom

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Ok got my seals and crank bearings...waiting on some Hondabond.

Next question:
When reinstalling the needle bearings into the case, do they get pressed in, just whacked in w/ socket & hammer? I have done many 4 cylinder rebuilds on subarus and lots of crazy stuff, so pressing in a bearing is no issue. But nothing this small and just tapping on then seems a bit detrimental. Im thinking of freezing them and warming up the case so I can just drop them in like I do with wheel bearings instead of pressing. Also pre-lube assembly lube, whats best if at all on these needle bearings? grease, oil, 2 cycle mix?

Well I drew them in with a nuts/washers and a bolt
 
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dangerousatom

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OK still in need of more help
Got the saw back together after splitting for bearing, bushing and seal replacement. Those seal are a PITA to get in ...only messed up 3 before making a seal driver from 1" copper sweat union and a 5/8 socket, then it went in like it saw its home!
Now I still don’t get any compression number when testing. The comp gauge goes up for a moment but holds no pressure. I can barley hear air leaking out on some tests. When unsung a syringe to add fuel to the carb directly does fire/turn over but stalls immediately, . Then ran a 2ft piece of tubing with fuel in it attached to the carb, as the tank is not installed yet but still nothing more then a rev and stall. I’ll assume then I’m not pulling enough vac to pull fuel?

Some bits I don’t quite understand , there’s a hole in the crank case that goes into the back of the manual oil pump. That is all installed and sealed up from what I can tell but will it pull vac through the oil tank if empty as there’s a weep hole with hair pin in it.

I sealed the case and jug with hondabond and let it setup for 24hrs. Everything was cleaned and surfaces well prepped, the cylinder looked and felt great along with the piston so what am I missing. I’m about to go buy a vac/pressure test gun to give it a leak down, what # should I look for if it holds and how long a duration.
 

countryhog

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Sounds like you may have buggered one or both of your seals. Also, sounds like your compression tester doesn’t have a Schrader valve to hold the reading. Aside from the fact that poulans are known for low compression, low hundred, your gauge should hold the result until you push the schrader valve
I’ve always thought installing the seals on craftsman/Poulan 3.7 (3400,3700,4000,etc) was pretty easy. One side of the crank is tapered, flywheel side, the other side has a shoulder; pto side.

Temporary Aside:
why are turds tapered?
So your butthole doesn’t slam shut. Ok back to the subject at hand

What you have to be careful of is when you install the pto seal is that you PROTECT the inside lip of the seal when going over the shoulder. I like to use a thin strip of somewhat rigid, but flexible, plastic. Call this the PROTECTOR. Some people use pop or beer cans. Use whatever you want but bear in mind that regardless of all the punishment the seal is subjected to the inner lip is really flexible and thus subject to tearing. If you use aluminum can MAKE SURE to totally debur the edges. Roll the protector, insert it into the seal, place it over the shoulder, gently nudge the seal onto the shaft, gently remove the protector. Grease is your friend. Tap the seal until it bites into the case then place a washer that barely fits over the shaft but is wider than the seal over the seal. Place a deep socket that will clear the shaft and fit on the washer and drive the seal home until the washer bumps the case. The washer keeps the seal from getting cocked.
First thing is to determine the state of compression though
Go forth and conquer.
 

dangerousatom

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Well it wasn't the rubber that was giving me the issue. The metal ring the seal body is made of was getting torqued up on an angle and then would get a kink in it. I have driven many a seal on subarus but this was smaller and a bit more delicate than i've done. After making the seal driver they were all good, so Im like 98% sure its not the seals that are leaking :facepalm: Dont want to split this case again and buy more seals, and its very hard for me to believe that its the case leaking where I hondabonded it all together. Need to get me that vac/pressure tester n soapy water it.
 

dangerousatom

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Yes but can you split the case with out wrecking the seals n then reassemble the case again with out wrecking them...? I guess you could particularly if it’s all clean before it’s really been run
 

countryhog

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Never tried.
dropping back a bit for a second. I just reread your first post and my response. Somehow I thought you were asking if the saw was worth some effort. My initial response to your first post was incorrect. Seals have nothing to do with compression. Compression is a measure of how well the slug, jug, and rings work together.
I sometimes just skim rather than study. I apologize if my answer led you to extra work and bucks.

I just put rings and seals in a 4000 and rebuilt the carb. Musta pulled the starter three to four hundred times over 2-3 days til my brain reminded me it takes air, fire, and FUEL for a saw to run. Tore it apart again. the screen was clogged. I had tried to reuse the original filter after cleaning it with carb cleaner. Apparently the fuzz from the filter broke loose and got sucked into the carb. Never again
 

dangerousatom

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Ok update......

So I looked at my comp tester, it all looked fine and has been barely used to begin with particularly on small engine testing size plug, schrader's are in good sealing condition. Here's the kicker, I decided to put a few shots of straight mix oil into the cylinder and crank area ( maybe 1-2cc via syringe ) and give it a good roll around with slow cylinder turn over. Now I have just under 160psi :banana: and it holds for a long time. So at this point Im waiting on a carb rebuild kit as one of the gaskets needed to be ripped to get it apart for inspection/cleaning.

I do have a question witch I cant seen to find on line. What is the turn out on the carb adjustment screws for factory setting? Im assuming 1.5-2 but I cant get a definitive answer. Im going to clean out the thing as much as I can before reassembly w/kit and its been tweaked for years by others who have run the saw into the ground before I got it.
 

countryhog

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Walbro I’m almost certain it’s 1 out on both h and l. I’ll check in a while and report back
 

dangerousatom

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Yes it’s the original Walbro 1n1 is a good start and I’ll go from there if need be. I’m assuming I’ll have to run it out a bit more now that it’s been ported and muffler modded long with a custom hi flow air filter.

Won’t get the carb bits till the Wed 15th so I got time

Hoping my cleaning/rebuild of the oil pump will work too?!?
 

countryhog

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My red craftsman 3.7 with muffler mod is:
L - 1-1/4
H - 7/8

what was your compression before shooting mix oil into the jug?
 

dangerousatom

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Rite On:thumbsup:

Couldn’t get a read on comp at all b4 straight oiling it.

Prior to the tear down I was seeing 135ish so I don’t believe the rings or cylinder is bad, and since the compression doesn’t fall at all now they must be in good shape. . . .?
 

countryhog

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This particular 3.7 of mine had low compression after rebuilding but did have compression Took a bunch of pulling and priming to get her to start.
Was the 135psi before or after porting?
 

countryhog

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So the 135 was before tear down and porting? Now, after porting you get zip? Wondering if the porting is at fault? Got any extra jugs you could try?
 

dangerousatom

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Lol!

Got to read it all Hog..... see post #11

I’m now holding a solid +155psi. No extra jugs as she’s the only craftsman 3.7 I got. Porting IMO shouldn’t have done a thing as it was very mild. Left n Right of opening was extended maybe 1/16-3/32 no measurable change on roof/floor. I did down ramp the roof before opening to cylinder and smooth out the walls along with smoothing the after carb plastic inlet piece.
 
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dangerousatom

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Its Alive! :headbang: and runs strong........got to tune the carb though
Now I need to replace the fuel lines cus it would seem harder tubing doesn't seal the tank hole and the fancy sintered breather leaks straight out :thinking:

 
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