Dominant saw V4 371 build

[Ronie]

If you use an OEM gasket and stack it on the Hyway gasket that should get you to around .020 squish if your measurements are right.

 

[Ronie]

I think you’ll need to try the solder method for squish. Your method is probably flawed and making you run in circles.

I’d be glad to mail you out a few feet of .026 and .033 solder. I actually use a drill to turn my saws over and check squish, I find it to be more accurate than rocking the flywheel back and forth at TDC.

You can stack gaskets if needed with a little sealant. I also have brass shim stock here in various thicknesses I can send you some of.

You beat me to the stacking gaskets. lol

 

[Marshy]

What's that gonna do to port timing, it just sounds to me like a good way to throw off numbers. The dominate piston is about .030 taller from pin to crown without counting the popup. Then include the cut intake skirt and exhaust cut that gives more ex duration, man alot of stuff going on here that is above my head

Well yeah, changing the base gasket thickness is going to change timing. I don't think its anything to worry about. Not like the saw is going to run terrible if you add 0.03" base gasket. Most people remove 18-20 though when they delete a gasket. Do you plan to do any porting?

You're limited in how to correct this. Pick your poison. Personally I would try claying the piston or at least get some thin electronic solder and double check the squish.

I know a guy using a lot of these pistons in 372 builds. I'll ask him if he noticed any issues like yours. I'll also ask if he gets the same measurement (pin to crown) 0.03" taller than the stock pistons.

 

[Marshy]

Ok, the word is that the distance from the cylinder flange base to the squish band varies a lot. Also, the Dominant piston purposely has a little taller crown height. He also said the 371/372 pistons had different crown heights depending on vintage.

My suggestion is to post your actual pin to crown measurements fir both pistons and see of another member will check a stock 372 piston. Or get a different cylinder. He said Hyway work well with those pistons.

 

[Funky sawman]

Thanks guys. I'm gonna try to either make a gasket or stack em. My measurements are flawed due to two things. I have been real shaky, and my cheap harbor freight POS calipers wont rezero each time I use them. It can vary by up to .010.
At this point in the game measurements are out. Shouldn't have to measure to begin with using a supposedly drop in piston. If I would have known this to be the case I would have saved 120 dollars and a whole bunch of headache

 

[blsnelling]

This is the second time I've heard of these issues with this version of Dominant piston. I wouldn't even consider running it. Sent it back for a refund.

 

[Funky sawman]

Fighting this saw has became worse than dealing with a horse that has colic!

 

[Funky sawman]

This is the second time I've heard of these issues with this version of Dominant piston. I wouldn't even consider running it. Sent it back for a refund.

Well sent them an email, hopefully this can get straightened out. Same issue with 2 cylinders I have which are built some 20 years apart. Do you mind going into a little more detail about you knowledge on the fitment issues? Thanks Brad

 

[Marshy]

Could be that your saw has the deck machined lower/closer to the center line of the crank. Maybe that saw was tight from the factory.

 

[Funky sawman]

In its form as a 365, it did seem to have more comp that the typical 365, or that could just be me getting weak lol

 

[blsnelling]

Well sent them an email, hopefully this can get straightened out. Same issue with 2 cylinders I have which are built some 20 years apart. Do you mind going into a little more detail about you knowledge on the fitment issues? Thanks Brad

It sounds like they've increased the crown height of the piston...too much. Also, a beveled crown on the exhaust side is not the correct way to set port height. It hurts both compression and squish velocity. Bottom line...the piston isn't made right. They need to recall all of these and fix the problems.

 

[blsnelling]

Could be that your saw has the deck machined lower/closer to the center line of the crank. Maybe that saw was tight from the factory.

This is not the first time this has been reported.

 

[Marshy]

This is not the first time this has been reported.

Yeah, I get that. There have been more saws that they have worked flawlessly for than not. If the piston is within the tolerances they decided on then their ain't a thing wrong with it, other than more modification needs to take place to use in this particular saw.

With a wide variation in deck to cylinder head height from the factory there are bound to be a few saws that it won't drop in. They will probably refund his money if asked.

 

[blsnelling]

I have used a Dominant piston as well. This is a new variation though.

 

[Wonkydonkey]

I feel sea sick watching that vid..

 

[Marshy]

I feel sea sick watching that vid..

Gotta get the piss out some times. Wasn't that bad.

 

[Funky sawman]

That's was my 13 y.o. son recording that action he is learning

 

[Funky sawman]

So does this mean were seeing a .020 difference in deck to crank centerline in these series of saws? That's assuming that the piston was designed to have .020 squish in their test builder

 

[Marshy]

So does this mean were seeing a .020 difference in deck to crank centerline in these series of saws? That's assuming that the piston was designed to have .020 squish in their test builder

Easiest way to tell would be to put that cylinder and piston in another 371/2 and see if the squish clearance changes.

 

[Funky sawman]

If only I had some spare cases laying around