Husqvarna 51/55 Squish numbers

[Matt D]

Hey Guys, so I'm new to the chainsaw scene but not new to 2 cycle motors, messed with a lot of snowmobile stuff. So I got a 51 that ran but had low compression, took off the cylinder and both the piston and cylinder were scored, ordered a 46mm top end and cylinder for it from china and received them today. After reading and watching some videos I'm contemplating doing a base gasket delete on the saw using some yamabond 4. I used the solder trick to measure squish, I measured in a few spots and got .035-.036 for squish, this seems like a lot as I read the ideal amount is .018-.020. Now I don't have the equipment or knowledge to cut the cylinder down or anything like that to get those squish numbers so is it even worth it in this case to do a gasket delete? Thanks for any help.

-Matt

 

[bretts]

I built a 51 for my dad, it had a scored p/c so I bought a 46mm top end from Hutzl and when it came in I had a good look at it. It was perfect, good chamfers, plating etc. I didn't need to do any cleanup on the cyl, made a notch on the case where the impulse hole on the cyl would be, deleted the gasket, applied some sealer to the cyl. It now has something like 30 litres of fuel run through it and it still runs strong.

 

[Dub11]

Yes from what I have read these saw will run good with that number and they come that way from the factory. I'll measure my 55 when I get home and see what it is. Its all stock. And that .018- .020 Is like the magic minimum number you want

 

[Matt D]

I built a 51 for my dad, it had a scored p/c so I bought a 46mm top end from Hutzl and when it came in I had a good look at it. It was perfect, good chamfers, plating etc. I didn't need to do any cleanup on the cyl, made a notch on the case where the impulse hole on the cyl would be, deleted the gasket, applied some sealer to the cyl. It now has something like 30 litres of fuel run through it and it still runs strong.

That's where I got my P&C from and same thing it came looking really clean.

 

[Matt D]

Yes from what I have read these saw will run good with that number and they come that way from the factory. I'll measure my 55 when I get home and see what it is. Its all stock. And that .018- .020 Is like the magic minimum number you want

Awesome, thanks

 

[PogoInTheWoods]

Your initial squish numbers are about normal for the decent aftermarket kits and will yield 160PSI+ compression numbers without a gasket and without ever firing up the saw for the rings to seat. I've used Meteor and Huztl with the same results. The key is a nice compact combustion chamber with these kits. If you start grinding away at the base you'll also need to take into consideration the effect that may have on the port timing. Usually not where you want to go with a simple top end repair on a 50 series Husky.

Also check the whole intake assembly for the typical problems there...., (stripped bulkhead threads, old intake boot and impulse tube). Usually why the top ends in these saws get toasted in the first place.

 

[Matt D]

Your initial squish numbers are about normal for the decent aftermarket kits and will yield 160PSI+ compression numbers without a gasket and without ever firing up the saw for the rings to seat. I've used Meteor and Huztl with the same results. The key is a nice compact combustion chamber with these kits. If you start grinding away at the base you'll also need to take into consideration the effect that may have on the port timing. Usually not where you want to go with a simple top end repair on a 50 series Husky.

Also check the whole intake assembly for the typical problems there...., (stripped bulkhead threads, old intake boot and impulse tube). Usually why the top ends in these saws get toasted in the first place.

Thank you for the reply, so I guess my initial confusion was I thought the .018-.020 was a number to shoot for on a base gasket delete without any grinding work. Good to know my numbers are within spec. I put the saw back together and without the rings seated it read 145 on my gauge. The 46mm cylinder without the decomp valve wears my arm out quick.

 

[PogoInTheWoods]

That .018 ~ .020 is as tight as you'd want to go before risking the piston hitting the top of the cylinder after everything heats up and expands.

 

[Matt D]

That .018 ~ .020 is as tight as you'd want to go before risking the piston hitting the top of the cylinder after everything heats up and expands.

Good to know!

 

[GoBigBlue1984]

I've ran .013-.015 on the 51/55's with no problems. I run 93 octane as well. Can't speak to the Chinese jugs but OEM 51 jugs have really small combustion chambers. I've had stock 51's pull 180 lbs w/gasket. Most are 160-170. But as these guys have said get squish to .020 and add a deflector to your muffler and you'll be happy with just those two simple mods.

Break it in and then come back and advance timing 1/3 off the key cast into the flywheel. Then you'll really notice a difference. About all you can do with 45mm/46mm open port jugs. I've raised and angled transfers toward intake but couldn't tell a difference.

 

[Dub11]

Sorry I haven't posted what I said I was going to post I just can't find my rollnof wire for the life of me. Dam thing is it was brand new lol.