Re-assembly of Husqvarna 50 (51/55) need timing and muff mod advice

[thefarmboy21]

Since before Easter I've been working on my Papaws late 80's model 50 Husky. I'm a pretty decent engine mechanic...but 2-strokes turned out to be more than I bargained for haha. Anyway, the saw had a ruined piston and cylinder, had them off in less than 20 minutes. 10 minutes and $23 on eBay later, new P&C kit on it's way straight from china. While waiting the 3 weeks it took to show up, I decided to look into some mods (here's where I learned it was over my head) I had no idea up to this point how all the ports and transfers made everyhing function and changed the timing. I also learned that since the original parts were only scared on the exhaust side, that it was likely that a 30 year old seal had finally failed and sucked air. "CRAP.....I really didn't want to split the case!" A few homemade tools, some JB weld and several lessons learned later and it's now back to an assembled case/crankshaft again. So here's where I need some help:

1. How much resistance should the crankshaft have in the case while turning to by hand? No flywheel or clutch, just bare shaft in the case.

2. What kind of timing specs should I shoot for? It's just a firewood/farm saw but I want it to run at it potential. And yes, I do have a degree wheel.

3. Does anyone have any photos and/or tips for a muff mod on this particular saw? The 50 muffler appears to be even more restricted than the 55's AND I'm not sure what to do with this massive baffle inside the muffler or what size outlet to give it.

4. After some minor mods, is it beneficial to use a different spark plug than OEM spec? I think the book actually calls for a champion which suprised me because I figured it would be NGK.

Those are the main things I need to know for now. I'm hoping to get thing finished soon. Thanks!

 

[thefarmboy21]

Anyone?

 

[cus_deluxe]

Hey dude,
Crank should roll somewhat easily with just finger and thumb. Want some resistance but not so much u have to really try at it. If theres a ton of resistance then a sharp whack on both ends of the crank helps to relieve stress of the crank after reassembly. Flywheel should be keyed, but a slight advance is usually ok. Youll get more out of removing the baffle in the muffler and removing base gasket if the squish allows. A little searching on this topic will fill you in on what i mean. Have fun!

 

[cus_deluxe]

Also the carb compartment flange on these is pretty notorious for leaking air as well.

 

[thefarmboy21]

Are they notorious for the flange leaking, or the weird slip fit rubber boot? Cause I really don't see how that thing works

 

[thefarmboy21]

How much advance would be good? Do I just shave the key and shim it X-amount one way?

I was really looking for more info on what degrees the ports should open and shut at rather than actual coil timing.

 

[cus_deluxe]

Well im by no means an expert (more like a complete tard) when it comes to timing #s. I understand the numbers, but very little of the theory that goes into deciding what are good #s for each saw, and they are all different. Advance the flywheel about half the width of the key, delete base gasket and a muff mod will yield significant gains on this saw. Anything beyond that will require more special tools and techniques.

 

[PogoInTheWoods]

Unless you're grinding ports and transfers, don't even consider messing with the timing numbers. Not worth it on a simple rebuild. Speaking of which, search "Husky 55 Rebuild" in the upper right hand corner search box on the page, grab a beer, and learn everything you need to know..., and then some.

Most important thing in all of this is to ensure case integrity and a sound intake assembly. A vac/pressure test is mandatory.

Great little saws. Good luck.

 

[sweidish445]

Now, im admittedly no expert on the 51's/55's.. i just recently went through my bosses 1998 55 rancher. The saw had great compression and no scoring so i didnt remove cylinder. Pressure test verified the suspected leak at the intake boot so i simply cleaned her up, all new gaskets, lines, filters, and starter cord. No muffler mod, but the saw cut great!! i couldnt get the intake boot to pass pressure test on its own so i used black permatex liquid gasket on boot and she held 100kpa for like 30min till i called it good.. i think thats 3x the pressure the book calls for. Havent tested this long-term, but have used it on another saw and it has held up.

Now, i just found a 1998 55(non-rancher) which had a smoked piston/cylinder.. i fixed the cylinder, and am in search of a piston.. i plan to go without base gasket, using loctite 518, and modify my muffler. I intend for this saw to be strong and reliable so i wont mess with much. I may grind polish and chamfer ports a bit, but im going to keep my timing close to stock.

I measured squish before removing the jug and without the base gasket puts me in the .026 range which is close to perfect.

Ive heard muffler port should be 70-80% of exhaust area. I am going to cut out the baffle, and also the small web under the deflector. Ive seen a lot of these saws with melted brake handles and clutch covers so again, nothing radical. In fact, i made an aluminum heat shield for my bosses rancher which i will make for mine also.. this is the difficult part since it must wrap the deflector so tightly.

The ngk bmr6a is also specified for this saw. I typically run ngk in most my stuff and have never had a bad plug. I would worry more about the air gap than the plug...

I have messed with ignition timing on my 338xp, but only because i sheared the flywheel key. I advanced about half keys width, or about 4-5mm measured at the flywheels outter edge. The nut should hold flywheel without shim. My 338 has NO key.. Not sure if it was the muffler mod or the timing, but that lil saw rips like my 445 did stock.. however, i do not intend to alter the 55.

 

[sweidish445]

And like pogo said, dont fire it up until it passes pressure/vac test..

 

[thefarmboy21]

How do I do a good vac/pressure test on this saw with the crappy style intake boot that it has?

Also where's the best place to get an economy tester that does both....my mighty vac seems to have taken a crap.

 

[PogoInTheWoods]

Use a spark plug adapter as your test insert point and then block off the intake at the bulkhead. If you don't have an adapter, you can make one from a spark plug, but bustin' the porcelain away can be a *****. Some RTV and a barb or some old fuel line and your in business. Husky also makes an adapter.

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And there ain't no econo-tester that does both vac and pressure. An 8500 is about as econo as it gets that'll do both. Should be able to get any part you need directly from MityVac if you have one that needs fixed or may even be able to find a killer deal on a new one if you shop around.

https://www.google.com/search?q=Mit...ome..69i57.17217j0j7&sourceid=chrome&ie=UTF-8

 

[PogoInTheWoods]

Was gonna add that you can also make an intake block-off plate from aluminum stock with a hose barb for for your test insert point, but those nylon threads are sensitive enough as it is and using the wrong screws or over tightening to the point of stripping would not be uncommon as they are the primary weak point of the design in the first place.

 

[sweidish445]

I make my own pressure test fittings. Made my plug hole adapter out of a piece i robbed from an automotive compression or leakdown test kit.. You may be able to clamp a rubber strip over the inlet and seal the impulse with a plug. That or female rubber cap and hose clamp may work? I made fitting for spark plug hole, so i just tested by sandwiching rubber between the carb and manifold like usual.

 

[sweidish445]

So Pogo, found a post of yours i believe describing the identification of the op and cp 55's... ive been scratching my head for a day or two over my 55 and "finding the correct piston." Haha.

Now, am i mistaken, or have i stumbled on a cp 55? Its a 1998 air injection 55. Non rancher. Has 45mm piston/bore. Old scored piston has a hiked skirt. Top cover tag shows 55 51cc.. now which has the +++ on cylinder?

I have no reason to believe the saw has been altered or rebuilt. Guy i picked it up from says he ran it for years till the shop told him it had low compression. So it aged for 2 years till i came across it.

Would love to get a piston and see this thing running..

 

[BGE541]

Why not include photos of the porta so we can tell you? Those 55s can be very strong saws with a little love. You may even be able to run a 350 piston that's designed to run with closed ports but you may have to trim the skirt some. Be sure to check your squish because the piston top above the ring groove is usually a few thousandths taller then the 55/51.

 

[sweidish445]

Not the best pic but its all i have for now.

 

[PogoInTheWoods]

Closed port. Looks pretty nice, too. Lil Red Barn is now selling the 45mm windowed piston for that cylinder. I've heard they're decent.

 

[PogoInTheWoods]

BTW, Meteor and Hyway make a very nice hybrid op/cp 46mm top end assembly as well.

 

[sweidish445]

this is what it looked like when i got it.. cylinder cleaned up real nice like. Also resurfaced exhaust port.. saw must have run with loose muffler for a bit. Haha

All in all, im pretty happy with my $35 find.. saw is actually in great shape and covers are all in good condition!

Didnt mean to take over the thread btw. Ill have to create my own for the full build. Thanks guys..