272 new build low compression

[cus_deluxe]

intake at 67? btdc?

 

[Stump Shot]

I checked squish 3 times but can’t hurt to check again. When I timed the saw when I first put it together I got
Exhaust 100
Transfers 116
Intake 67
That is with no base gasket. I don’t know enough about timing yet to know how much those numbers where they are would affect compression. I did think the exhaust may be a little high stock? I thought it would be somewhere around 105.

If your compression tester has an adapter on it, this can alter the reading in a small 2-stroke engine like a chainsaw.

 

[rfarr94]

If your compression tester has an adapter on it, this can alter the reading in a small 2-stroke engine like a chainsaw.

It has a schrader valve on the end of the threads a tube right up to the gauge that has pressure release on it.

 

[rfarr94]

67 btdc. I’ll re time it tonight. Trying to do everything a couple of times to make sure I’m not overlooking something stupid or obvious,

 

[cus_deluxe]

im guessin u have a combination of things. a little extra ring gap and a huge chamber would go a long way toward low compression.

 

[Mastermind]

I checked squish 3 times but can’t hurt to check again. When I timed the saw when I first put it together I got
Exhaust 100
Transfers 116
Intake 67
That is with no base gasket. I don’t know enough about timing yet to know how much those numbers where they are would affect compression. I did think the exhaust may be a little high stock? I thought it would be somewhere around 105.

Timing numbers sound right. That 67 is from TDC.....right?

 

[davidwyby]

I hate to be repetitive, but try oil in the chamber for the test.


You can measure the volume of the chamber or compare to a good one (you have the old cyl?) with water.

 

[Stump Shot]

Timing numbers sound right. That 67 is from TDC.....right?

The casting voids(ports) have to be pinned on after the cylinder mold is made.
At this point there are two choices, treat it like a finely tuned mechanical thing that it is, or treat it like Mr. Potato Head.

 

[p61 western]

Is this a bad time/place to sell a Hiway 272 top end?

 

[Kiwioilboiler]

Is this a bad time/place to sell a Hiway 272 top end?

Is it compression tested?

 

[Lightning Performance]

I’ll bet on port timing being messed up and bleeding off compression. Or maybe the chamber is too big. Oil in the cylinder with the compression test would be telling as to whether the problem is ring seal or not.

My opinion with the AM stuff is that you can’t trust it, so you have to have a real qualified guy like one of the porters on here go thru and check and correct it...but the quality/durability/longevity is also suspect, so it’s kinda like throwing good money after bad to pay a good guy to make it fly...the only way I see it making sense is maybe for a saw where OEM néw or used is NLA and the builder can verify that everything is correct (timing wheel, etc.) himself...?

Good summation.

Buying cylinders in bulk fixes most of the issues a builder will come across. Some just don't make the cut. You can buy pistons in four packs and more packs. When doing a V8 order ten and hope you have enough to match up for a build. Seen guys order twenty and then give up on a company cause they couldn't fill a four banger for street use, oh my. Some batches of parts are good and others not so much. Like monkey man said. A, B or C all = $

 

[p61 western]

Is it compression tested?

Negative buyer beware

 

[Mastermind]

Is it compression tested?

We don't need no stinkin compression. If you don't believe me, ask PotMetalPony.

 

[Stump Shot]

We don't need no stinkin compression. If you don't believe me, ask PotMetalPony.

Just don't over port the exhaust where it's made and you'll be fine.

 

[rfarr94]

Timing numbers sound right. That 67 is from TDC.....right?

Probably a stupid question, but when you say from TDC is that the same as before top dead center? Don’t you time intake before top dead center or am I doing something wrong when timing?

 

[huskihl]

Probably a stupid question, but when you say from TDC is that the same as before top dead center? Don’t you time intake before top dead center or am I doing something wrong when timing?

Before and after tdc will give the same reading. Easy way to tell your wheel is centered

 

[drf256]

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

Odd. Most are wider in skirt. More thermal expansion in crown.

 

[Nutball]

45mm bore (44.96mm), Piston: 44.90mm top to bottom

 

[Lightning Performance]

45mm bore, 44.90mm top to bottom

What are you measuring with?

 

[Nutball]

The usual.

https://opeforum.com/threads/piston-base-gasket-cylinder-measurements.20928/#post-1097038