660 Build = Low Compression??

[stinkbait]

I just finished up a ms660 build where I used an aftermarket 54mm cylinder and a 288xp piston. I cut the squish and base to bring the exhaust down to 98° and ended up at .022" squish. I cut enough from the chamber to where I had to ad a shim to the plug to index it so that it didnt hang below the squish band. I used job weld on the intake. Ended up with ex- 98 trans- 123 and in-83. What's puzzling to me is I'm only getting 155 psi after a couple heat cycles. Do y'all think the low compression is due to crappy aftermarket ring? I'm used to these numbers producing serious compression. Here are some pics of the cylinder roughed in. Didnt get any after it was done.

Sent from my SM-G930V using Tapatalk

 

[Deets066]

AM crap would be my guess

 

[mettee]

Or a bad compression gauge

 

[Stevetheboatguy]

Ring gap?


Steven

 

[drf256]

My bet is the ring not being seated yet. I always go with a caber ring(s).

Try a little light oil in the cylinder with piston at TDC. Let it get around the ring. Try it again.

You’re into the plug threads. I can’t see how it’s 155, unless that AM chamber is huge, or your bore is out of round.

I stopped using AM internals (other than meteor/caber). It’s just a guessing game.

 

[Wonkydonkey]

I’m guessing you did a p&v test.

decomp valve ?

Have you tried adding a little oil into the cylinder to help seal the ring see if that increases the compression. ?

Other than the above, you may have to tear it down and check the cylinder for scoring and check the ring end gap,

 

[Wonkydonkey]

@drf256 beat me to it with the oil check/seating

 

[stinkbait]

I pulled the muffler last night. Theres no scoring. I may order a cane ring and give it a go.

Sent from my SM-G930V using Tapatalk

 

[smokey7]

With that much out of the chamber that should be well over 200. Check with another gauge first. Then pull the jug and it should be obvious what the issue is by looking at the wear pattern on the jug. Bad tester Ring tension or jug out of round are the 3 most likely causes. Jug looks pretty decent as far as the playing. What brand of jug is it?

 

[stinkbait]

Its farmertec jug and slug. I may just order a cross cylinder set and give it the same treatment. I'm gonna cut with it some this weekend and see if the compression comes up any.

Sent from my SM-G930V using Tapatalk

 

[smokey7]

The numbers should make a dang good runner. Looks like you raised the intake a mile. Prolly was near 90 before you epoxied it up to 83? Compression isn't a be all end all. I would run it as long as it ran good and then move on after it started getting tired. Please give us a vid of it running.

 

[stinkbait]

I'll definitely make a video if the weather allows this weekend. It should still perform better than stock. I ordered a caber ring for it today. And, I finally jumped on the band wagon and ordered one of those mmws cross performance cylinder kits for later down the road. This saw may become my milling saw just the way it is and my other 660 will get the cross setup with similar port work.

Sent from my SM-G930V using Tapatalk

 

[Redfin]

How much did you take from squish?

 

[stinkbait]

How much did you take from squish?

I'll have to look at my notes when I get home. I'm pretty sure it was in the neighborhood of 0.050".

Sent from my SM-G930V using Tapatalk

 

[Deets066]

I'll have to look at my notes when I get home. I'm pretty sure it was in the neighborhood of 0.050".

Sent from my SM-G930V using Tapatalk

.050 - .055 sounds about right. Any more than that and you’ll have problems keeping the ring tucked in on the intake

 

[MG porting]

Its farmertec jug and slug. I may just order a cross cylinder set and give it the same treatment. I'm gonna cut with it some this weekend and see if the compression comes up any.

Sent from my SM-G930V using Tapatalk

There rings aren't the greatest I would change them out with the caber rings if you find out if the gage is correct.

 

[a. palmer jr.]

Be sure and check the Caber rings when they arrive...I've bought them before and once they didn't fit the piston, too large and no ring gap...I'm sure the ones they sent me were for a different saw than the ones I ordered..

 

[Wood Doctor]

Be sure and check the Caber rings when they arrive...I've bought them before and once they didn't fit the piston, too large and no ring gap...I'm sure the ones they sent me were for a different saw than the ones I ordered..

Same thing happened to me years ago. I decided after that to always by the piston and cylinder kit in one package.

 

[stinkbait]

Compression coming up. Ran 3 tanks through the saw this morning. 28" bar with 8 tooth 3/8 sprocket is like a laser beam going through wood. Ran a 24" bar with. 404 and seven tooth sprocket also. Here's a video of it with the .404 7 tooth. This bar and chain are straight out the box. The .404 could use some work from the factory. Still cut good, but not as hood as smooth as 3/8". Will get a video with 3/8" soon. Hit metal with it in the base of a tree and just switched over to the .404. Sorry about video rotation. My wife is responsible for that.