272 new build low compression

[Stump Shot]

I have a used OEM 268xp P&C I could let go real reasonable.
@rfarr94 PM me if interested.

 

[Maintenance Chief]

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.

I take it ,you've already cleaned off the sealant that you used in these pictures?

 

[timg]

I'm gonna look like an idiot here on this question @rfarr94 . I don't see the impulse port in the crankcase to mate up to the cylinder. All of the ones I've done had a port in the crankcase top machined area to mate up with the cylinder bottom porting. I assume you have the standard intake that the 272 uses? And it looks as if your cylinder port would be blocked with this crankcase.

 

[timg]

Only reason I ask are your running symptoms. I had the same issue with one. Only to find someone had the wrong cylinder gasket blocking the impulse port. It would start after several pulls but had no power in the cut. Soapy water verified decomp plug and spark plug are leak free??

 

[Ronie]

I'm gonna look like an idiot here on this question @rfarr94 . I don't see the impulse port in the crankcase to mate up to the cylinder. All of the ones I've done had a port in the crankcase top machined area to mate up with the cylinder bottom porting. I assume you have the standard intake that the 272 uses? And it looks as if your cylinder port would be blocked with this crankcase.

The crankcase has a cut out that matches up to the impulse hole on the cylinder.

 

[Maintenance Chief]

I'm gonna look like an idiot here on this question @rfarr94 . I don't see the impulse port in the crankcase to mate up to the cylinder. All of the ones I've done had a port in the crankcase top machined area to mate up with the cylinder bottom porting. I assume you have the standard intake that the 272 uses? And it looks as if your cylinder port would be blocked with this crankcase.

Yeah the fact that it won't start with out choke even warm had me thinking about this also.

 

[timg]

I saw that Ronnie but it didn't look close to me. Thx.

 

[rfarr94]

Quit wasting your time and money on that Chinese junk.

That is definitely going to be my thinking going forward after this. I’ve contacted the company I bought it from so hopefully they can make it right but we’ll see.

 

[rfarr94]

Yes the sealant has been cleaned up. I used an oem base gasket originally and had the same trouble starting.

 

[Mastermind]

That is definitely going to be my thinking going forward after this. I’ve contacted the company I bought it from so hopefully they can make it right but we’ll see.

It's not that they can't make a quality product. They just don't care. They will box up the garbage, and sell it just the same as the good parts.

 

[davidwyby]

Yeah the fact that it won't start with out choke even warm had me thinking about this also.

I went thru a similar issue with an AM PnC someone else installed on my 2159.

My half-theory on the choke is that it needs extra fuel to make enough compression to fire.

 

[p61 western]

I have a used OEM 268xp P&C I could let go real reasonable.
@rfarr94 PM me if interested.

Really nice piston. Lol

 

[p61 western]

I got this same top end with a project saw. @Stump Shot talked me out of using it, and now I'm really glad he did after seeing the trouble in this thread.

 

[Maintenance Chief]

Speculation about how the saw won't start because of compression is part of the issue, I have 2 very bad project saws with probably 50-70 lbs of compression that will run ?, hell I've got a 10-10 with the rings smeared into the piston that will actually make a cut.
Any measurements of the wall clearance or port timing will show an obvious problem? Right? Its not like its rocket science.
I'm not trying to get anybody's panties in a bind but a " defective" part should have a fairly apparent defect from manufacturing if it won't function and now I'm curious.

 

[davidwyby]

Speculation about how the saw won't start because of compression is part of the issue, I have 2 very bad project saws with probably 50-70 lbs of compression that will run ?, hell I've got a 10-10 with the rings smeared into the piston that will actually make a cut.
Any measurements of the wall clearance or port timing will show an obvious problem? Right? Its not like its rocket science.
I'm not trying to get anybody's panties in a bind but a " defective" part should have a fairly apparent defect from manufacturing if it won't function and now I'm curious.

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...?

 

[cus_deluxe]

idk, .015 seems like a lot of ring gap for 52mm right outta the box. an extra 5-6 thousandths on that can lead to low compression. also, are you POSITIVE on your squish measurement?

 

[cus_deluxe]

also, that chamber looks massive. id be curious to try to compare chamber size to oem.

 

[rfarr94]

It's not that they can't make a quality product. They just don't care. They will box up the garbage, and sell it just the same as the good parts.

Yeah I guess even if they make 100 good ones for every bad one you never know when your going to get the dud. And for 70 extra dollars I could have gotten oem and know I’m getting something but at least I’ll know for next time.

 

[rfarr94]

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.

 

[Stump Shot]

Really nice piston. Lol

Tis true. Lol