Saw timing advice.

[Kiwioilboiler]

Hi.

I sometimes feel abit inadequate when the cool kids are quoting timing numbers so I invested in a wheel, wrecked a power drill for its chuck and slapped it on my 372 for learning and stuff.

The saw has OEM Mahle jug, no base gasket and a Meteor piston.

My measurements, done and re-done and again a few more times:...
Exhaust opens @99 degrees ATDC, duration of 158 degrees.
Transfer opens at 125 degrees ATDC, giving 26 degrees of blowdown. (Had a lot of trouble reading these, my eyecrometer seems to have a lot of variance. Went to pushing a ring up and removing jug in order to get any accuracy and repeatability)
Inlet opens 74 degrees BTDC, giving 148 degrees of duration.

Now I'm not looking to port this cylinder, purely trying to upskill mentally.

Are these results within the realms of possibility for an unground 372?

If not, what may I have done wrong?

Cheers for advice today too @markds2 you're a legend.

 

[P.M.P.]

Hi.

I sometimes feel abit inadequate when the cool kids are quoting timing numbers so I invested in a wheel, wrecked a power drill for its chuck and slapped it on my 372 for learning and stuff.

The saw has OEM Mahle jug, no base gasket and a Meteor piston.

My measurements, done and re-done and again a few more times:...
Exhaust opens @99 degrees ATDC, duration of 158 degrees.
Transfer opens at 125 degrees ATDC, giving 26 degrees of blowdown. (Had a lot of trouble reading these, my eyecrometer seems to have a lot of variance. Went to pushing a ring up and removing jug in order to get any accuracy and repeatability)
Inlet opens 74 degrees BTDC, giving 148 degrees of duration.

Now I'm not looking to port this cylinder, purely trying to upskill mentally.

Are these results within the realms of possibility for an unground 372?

If not, what may I have done wrong?

Cheers for advice today too @markds2 you're a legend.View attachment 266253 View attachment 266254

Pretty cool this is how it starts

 

[huskihl]

Yeah you’re probably pretty close. I would’ve thought the exhaust would’ve opened more like 102. Yours at 99 would actually give you 162° of duration, 81 down to bottom dead center and 81 back up to closing off

 

[Kiwioilboiler]

Yeah you’re probably pretty close. I would’ve thought the exhaust would’ve opened more like 102. Yours at 99 would actually give you 162° of duration, 81 down to bottom dead center and 81 back up to closing off

Ta, i'll rip it all off tomorrow and re-install and re-time just to re-check it. My 99 was with the tiniest bit of torch light sneaking thru the very top centre of the port, maybe 102 is more accurate but in my case that would be a whole lot more light ingress.

 

[drf256]

Gotta use a ring, it’s the only way to know.

As for the light method, shining from outside and looking through plug hole gets me close. Shining through the plug hole and looking through the ex port definitely has tricked me into thinking the piston was at a much higher degree opening than it actually was.

Once you machine the jug, everything changes.

 

[Kiwioilboiler]

otta use a ring, it’s the only way to know.

For all three measurements Doc, or specifically transfer?

 

[drf256]

Exhaust and transfers with a pick. It’s the only real way. And then you have the bevels to deal with. On some saws, the factory bevel on the ex port can approach 5*.

The intake, you have no choice but to view through the intake port, or you can use a software program. I usually take a bit from the center of the floor at a time till I am where I want to be. It’s very easy to go too far with the intake floor. It moves very fast. If you leave a little center divot that’s a degree or 2 more than you wanted, it won’t hurt anything.

 

[Kiwioilboiler]

Exhaust and transfers with a pick.

So use a seal pick with a suitable tip angle to fish down the plug hole until it will poke into the port in question as piston exposes it?

 

[Redfin]

You can also use .023” mig wire through the ex to get uppers. Add a couple degrees.

 

[markds2]

So use a seal pick with a suitable tip angle to fish down the plug hole until it will poke into the port in question as piston exposes it?

I was going to ask exactly the same question!!

 

[drf256]

So use a seal pick with a suitable tip angle to fish down the plug hole until it will poke into the port in question as piston exposes it?

I install 2 studs into the base of the case/base pad diagonal from each other. Then I install gasket if I am gonna run one.

Put ring in bottom of jug with gap that won’t catch in a port, then install over piston at BDC. This is, of course, after you got your timing wheel zeroed in.

Then turn flywheel till wheel somewhere near original guesstimate of port, holding pressure on top of jug with hand. Pull jug, see where you are, readjust ring and retry until you can use a pick and feel/see that ring is flush with opening. That’s the only real way of knowing and being to reproduce results. Check timing wheel for reading.

If the crank won’t rotate easily, pull jug and check ring. In general for timing only, you can center the ring gap in the intake port and it won’t catch. Once you get near an edge, it catches easily on the port. Of course, you can’t run a ring gap in a port.

 

[Kiwioilboiler]

I install 2 studs into the base of the case/base pad diagonal from each other. Then I install gasket if I am gonna run one.

Put ring in bottom of jug with gap that won’t catch in a port, then install over piston at BDC. This is, of course, after you got your timing wheel zeroed in.

Then turn flywheel till wheel somewhere near original guesstimate of port, holding pressure on top of jug with hand. Pull jug, see where you are, readjust ring and retry until you can use a pick and feel/see that ring is flush with opening. That’s the only real way of knowing and being to reproduce results. Check timing wheel for reading.

If the crank won’t rotate easily, pull jug and check ring. In general for timing only, you can center the ring gap in the intake port and it won’t catch. Once you get near an edge, it catches easily on the port. Of course, you can’t run a ring gap in a port.

Gotcha! So sneak up on the readings using the pick on the removed cylinder to check for perfect alignment of ring bottom and port opening edge.

 

[Kiwioilboiler]

So because i could, i chucked all the timing gear on my 01 2171. Used Dr Mofo @drf256 ring method for finding last position of exh being closed and transfer, running scriber across the ring to port edge transition. I then used the 2171 case to re-time the 08 372 cylinder (372 case is now split for bearings and seals) in my original post. Numbers almost identical.

105 exhaust
130 transfer for 25 blowdown
75 inlet

Now to read up on what all this means......