272 new build low compression

[Bob Hedgecutter]

So basically it was a husqvarna part that failed ?

No fair- until the part number can be authenticated on the shaft key- after all, it was the key that failed.
More importantly- how does a flywheel swap increase compression? I might need educated on that one.

 

[hotshot]

Curious too, because I’m ordering a case of them if it works!

More likely the 272’s piston return spring was weak & a new one fixed it!

 

[lone wolf]

No fair- until the part number can be authenticated on the shaft key- after all, it was the key that failed.
More importantly- how does a flywheel swap increase compression? I might need educated on that one.

That's a good question I was wondering the same thing!

 

[rupedoggy]

I was too until I thought about maybe as the compression came up it then caused the flywheel to slip a little. After all the starter only turns the flywheel NOT the crankshaft unless it is solid to the flywheel.

 

[lostone]

I was too until I thought about maybe as the compression came up it then caused the flywheel to slip a little. After all the starter only turns the flywheel NOT the crankshaft unless it is solid to the flywheel.

I could see what you are meaning rupe but if the flywheel was spinning completely then the saw would have never ran to begin with or continued running, advancing the flywheel or not if the crank is turning completely over in order to make the saw run, which he states it was, means that the piston was making rotation and a compression tester wouldn't care if the timing was off either way ????? Maybe I'm over thinking it and not seeing the forest for the tree's.

 

[rupedoggy]

They say even a broken clock is right twice a day. Could not a flywheel stop in the correct position once in a while? Especially if a little stub of key was there and the wheel was pretty tight on the shaft.

 

[Huskybill]

Broken key the crank doesn’t turn all the way to full compression the flywheel slips on the crank stud. Your taxing my mind on this one what little I have left.

 

[RED-85-Z51]

Didn't you try the top end on a different saw and had the same 120?

Sent from my SM-G996U using Tapatalk

 

[lostone]

Broken key the crank doesn’t turn all the way to full compression the flywheel slips on the crank stud. Your taxing my mind on this one what little I have left.

I would say that could be an option if the saw wouldn't run, however he stated that the saw had low compression but was running. If the key was sheared and slipping that much then the saw would not start and run since the flywheel would not turn the crank over enough to start the saw is what I was getting at.
Now lets say the key sheared and the flywheel turned almost 360 degree's minus the width of the key in degrees and the saw was capable of starting and running with the timing being retarded that much, I could see the saw being without much power and causing the issue he is saying on running power but even at that point a compression test is still a compression test and it would be turning the crank over and reguardless of ignition timing compression would be compression? Or again I may be missing something, which wouldn't be the first time for me.

 

[Huskybill]

I’m stumped then.

 

[Gord404]

I think we are missing a few pieces to this puzzle, cabers are a very hard material and take about 10 tanks to fully break in, the rest is a mystery.

 

[rob066]

I think we are missing a few pieces to this puzzle, cabers are a very hard material and take about 10 tanks to fully break in, the rest is a mystery.

I used a new OEM cylinder on my 272 build. I put in a caber F cast since it was a new perfect bore. It took like 15 tanks for my saw to reach max compression.

 

[J D]

Did the cylinders fitted have decomp?

 

[rob066]

Did the cylinders fitted have decomp?

Mine did, but i plugged the decomp.

 

[J D]

Was wondering about the OP's saw as an accidentally pressed (or faulty) decomp might explain some of those low readings.
I recently had a saw with short pull chord that I couldn't get enough revolutions out of to get a proper reading... If I recall correctly that came up around 120psi but was definitely more

 

[Bob Hedgecutter]

Was wondering about the OP's saw as an accidentally pressed (or faulty) decomp might explain some of those low readings.
I recently had a saw with short pull chord that I couldn't get enough revolutions out of to get a proper reading... If I recall correctly that came up around 120psi but was definitely more

Right there in the very first post of the thread.......

I put a Hyway 272 top end kit on a husqvarna 61. It came with a pop up piston and caber rings. I plugged the decomp hole. When I first built it I did a compression test and only came up with like 116 psi.

 

[J D]

Right there in the very first post of the thread.......

I put a Hyway 272 top end kit on a husqvarna 61. It came with a pop up piston and caber rings. I plugged the decomp hole. When I first built it I did a compression test and only came up with like 116 psi.

I was thinking for the second cylinder... pretty easy to accidentally press it if you're doing a compression test on a half assembled saw & holding it down by the cylinder

 

[czyhorse]

After a new ring and piston job on my 365 / 372 (broke a ring trying to mod the 365 to a 372). I could not get pressure or vac test to work right. Suspected the decomp valve. Swapped it out for a plug and it passed no problem afterward. And the compression is unbelievable now. It didn’t ever have that much compression before. Sometimes it felt like it had little to no compression and it was only 6 months old. Now it is a beast to pull over. But it Starts faster and runs like never before. It has made me very suspect of decamps. I think it has been leaking by since I bought it new from the dealer which would I think explain tuning problems I had been having. I could never quite get it up to factory spec RPM.

 

[lostone]

I've still got a 372OE build that I'm not crazy about the comp test on as well. I was hoping that something I was missing would pop up in this thread and give me a hint as to why it was doing it. I bought two AM cylinder kits (Nikasil) and the first one with the rings that came with it are doing fine, the second one I even put a Caber ring in and it's mediocre at best. I'm hoping after some running that the ring will set and help the compression on it. I DID NOT measure the bore and piston on them before assembly and I wish I had now. I did set the ring end gap on the second one around .004 if I remember correctly.
It's just strange that the first one I pretty much just ported and threw together and I took my time with the second build and the first one has the second one beat and doesn't even try. At this point I'm thinking Gremlins.

 

[Gord404]

Ring end gap at .004 seems a little tight , usually around .008 to .010, what A M cylinders are you using and what is your squish. Had a 372xp I did up a couple of years ago and was quite disappointed in its performance and about 4 or 5 tanks later it came alive big time, caber ring and slightly re-worked Meteor cylinder