272 new build low compression

[Bjorn]

Hello, have you check airleaks?

 

[rfarr94]

I’ll have to check with the ring when I get home. I haven’t checked for air leaks but i didn’t see how they could affect compression being below the piston ring it should be sealed off from anything below the ring but I could be completely wrong.

 

[Bjorn]

If you have leakes, a smaller amount of fuel and air Will be delivered to the combustion Chamber, so the compression Will be lower If you have a leak.

 

[Nutball]

I think I've seen oval Hyway piston. Not sure how they can make them oval, but that's what the calipers say.

 

[Mastermind]

I think I've seen oval Hyway piston. Not sure how they can make them oval, but that's what the calipers say.

They actually should be bigger across the skirts than they are at the crown.

 

[Nutball]

I'm talking about an oval crown. I'll measure tonight.

 

[rfarr94]

I was of the thinking that if you had an air leak the same volume would be sucked into the crankcase. It would just be sucked in from places other than the carb so you would have less fuel and oil in the mix and that’s why top ends burnt up with leaks but compression would remain the same because the same volume was drawn into the case. Unless your decomp or spark plug was leaking then I could see a loss in compression. Just how my mind looks at it, though it may be completely backwards.

 

[Bjorn]

Hi, gasoline seals better than air. and leaks the crankseales, the fuel mixture goes out when the piston goes down.

 

[Maintenance Chief]

Even if the overall piston is misshapen the rings are contacting the bore and should seal well enough for a decent compression reading , cabers appear to be quality rings also, I've used several sets.
With a squish being .018 should make it very stout to pull over ? That would be about the limit squish for me, that son of gun should just hang by the pull cord all day long!
Being difficult to start with out the choke? There's about 50 things you could check but I'd tear that thing down again, maybe some of the sealant blew out from the base , seam gasket on the case is interfering with the cylinder? Who knows ,but with your numbers that thing should pop to life pretty darn quick! And unless it's your spark plug not sealing your more than likely not going to be able to repair the problem without a tear down.
Just my suggestion, of what I'd be telling myself in my head.

 

[Lightning Performance]

Broken rings or the wrong size rings can cause low compression.

 

[rfarr94]

Checked the ring end gap. I put the ring in the cylinder and used the piston so it was above the exhaust port and used feeler gauges to measure the gap. Came up with .015 had just a little resistance between the rings. Don’t know much about where it should be. Is that too loose or about right?

 

[rfarr94]

Being difficult to start with out the choke? There's about 50 things you could check but I'd tear that thing down again, maybe some of the sealant blew out from the base , seam gasket on the case is interfering with the cylinder? Who knows ,but with your numbers that thing should pop to life pretty darn quick! And unless it's your spark plug not sealing your more than likely not going to be able to repair the problem without a tear down.
Just my suggestion, of what I'd be telling myself in my head.

Yeah I was hoping the low compression was the reason it didn’t want to start right. I guess once I figure out what’s causing that ill move onto the next problem.

 

[Lightning Performance]

Checked the ring end gap. I put the ring in the cylinder and used the piston so it was above the exhaust port and used feeler gauges to measure the gap. Came up with .015 had just a little resistance between the rings. Don’t know much about where it should be. Is that too loose or about right?

Every manufacturer has a spec. 0.010 for every inch of bore will get you close most times. Your ok at 15. I've put new cheap rings in were 65 lol.
Someone did something wrong somewhere. NOT as advertised

 

[p61 western]

If the cylinder is a little more out of round than usual when, it could take much longer to break in and explain the low comp.
Not a big fan of the pop up piston for performance as a whole, true they can add some grunt at times, they also can loose a lot of zip.

What timing that this thread shows up lol. Curious to see what happens with this saw.

 

[Ronie]

I would plug up the decomp and check it again.

 

[Nutball]

They actually should be bigger across the skirts than they are at the crown.

Not according to Echo. The 590 piston is the same from top to bottom. Very tight tolerances compared to AM as to be expected.

 

[rfarr94]

Decomp has been plugged since I put it together. I’ve got another 61 maybe I’ll put the 272 top end on that and see if I have the same results.

 

[Maintenance Chief]

Pictures of said, P/C when removed .

 

[rfarr94]

Here’s the piston and cylinder. Looks like a little transfer where the skirt looks tight I guess but that’s all I see. No marks can be felt with a fingernail. Swapped to the other bottom end and same 120 compression. Decomps not leaking and cylinder didn’t look out of round at all when I shined a a light behind the ring. Im going to call hyway tomorrow. Something is definitely wrong but I sure don’t know what it is.

 

[Mastermind]

Here’s the piston and cylinder. Looks like a little transfer where the skirt looks tight I guess but that’s all I see. No marks can be felt with a fingernail. Swapped to the other bottom end and same 120 compression. Decomps not leaking and cylinder didn’t look out of round at all when I shined a a light behind the ring. Im going to call hyway tomorrow. Something is definitely wrong but I sure don’t know what it is.

Quit wasting your time and money on that Chinese junk.