Husqvarna 50 vs 51 differences?

[Pioneer]

Are there any discernible differences between the two saws? I have one with a 51 recoil cover and other parts labeled 50 on it.

 

[TLG]

One main difference is in the flyside crankcase half. The 50 doesn't have the air filter ducting or a way to secure it. The 51 & 55's had the air ducting and castings in crankcase to secure it. That was the start of the term turbo. It blew the air filter down to keep it clean in operations. Almost all other parts will interchange. But there will be others along to help with that.

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[Pioneer]

So is this a fifty then? Yeah, it's pretty dirty, quite possibly one of the dirtiest saws I have worked on.
When you pulled on the recoil the air filter would want to collapse. With all that dirt compromising the cooling, it's a wonder the piston/cylinder looks as good as it does.
It gives me 120 psi. Is this around normal for a single ring piston?

 

[s sidewall]

That's what you call Lack of Maintenance. But I've seen worst.

Steve Sidwell

 

[Huskvarna hotellgäst]

It's a 50. In Australia 51 had the later air filter and choke vane in the carb.
Almost all other parts are interchangeable. If you remove the flywheel, just be careful replacing it. Some have 2 keyways at 90deg. The one marked '4' is for the 40.

 

[raumati01]

I think some of the older white top 50s wont fit the 55 barrel which is the obvious upgrade if the barrel is smoked.

 

[cus_deluxe]

50s are 44mm, 51s and closed port 55s were 45mm, open port 55s were 46mm. and as said above, 51/55 cylinders have a different base diameter on the cylinder, so they wont fit on 50s. other than that, parts more or less interchange.

 

[Pioneer]

Tore them apart, and found out something interesting, they changed the cylinder base diameter on the saws somewhere down the line, one of the saws actually had a 45mm piston/cylinder on it. Probably a replacement, but there was plenty of room for something larger. Both had the same cylinder bolt mount dimensions though. I now have three of these saws, two of them have the larger cylinder base opening, and one of them has a different style flywheel with a wider crank key. All the same carb though, The walbro wa.
I also noticed the depth of the transfer ports are shallower on the bigger cylinder, maybe you loose top end power but gain mid range torque with the bigger jugs?
The saw with the smaller diameter piston had low compression of 120lbs even though the piston/cylinder was in very good shape. I found out excessive ring end gap was the problem, probably 3x the amount the bigger piston had. What is ideal ring end gap on this saw?

 

[cus_deluxe]

it may be that the black top 50s shared the later bolt pattern with 51/55s.

 

[grizz55chev]

So is this a fifty then? Yeah, it's pretty dirty, quite possibly one of the dirtiest saws I have worked on.
When you pulled on the recoil the air filter would want to collapse. With all that dirt compromising the cooling, it's a wonder the piston/cylinder looks as good as it does.
It gives me 120 psi. Is this around normal for a single ring piston?

120 psi is on the low side, it’ll run, just not with power.