440 timing numbers

[JTV10]

I got a ms440 with a cooked p&c for free. I got a meteor p&c for it and ran 2 tanks thru it with a 24” bar. I was not impressed. So i checked port timing and got the following numbers exhaust 101, transfers 115, and intake 70. Do these numbers look ok? I am just looking for a good firewood saw not a racing saw. Any advice if i should try my hand at moving these numbers around?

 

[huskihl]

Check your timing numbers again with a ring in the bore. Bolt the cylinder back down, set the timing wheel to where you suspect the port opens, remove the cylinder and then feel for the correct height with a pick or a tuning screwdriver.

If your numbers end up being correct, you have a couple options. If it doesn’t have great compression, you could have the jug sent out to tighten up the squish, which would also lower your openings a bit. And then you could raise the exhaust port up slightly to where you had 18–20° blow down between the exhaust and transfers. If you didn’t want to send it out, you could raise the exhaust up a little bit more to where you still had 18–20° between them. Raising the exhaust will lose some compression

 

[JTV10]

So i checked the numbers with a ring and they look like they were right.

i also checked squish and it came in at 34 thousands. So if i delete the gasket it should drop the cyl 10-15 thousands to increase compression? Then i could raise the exhaust port to get in the 20 degree blowdown range?

 

[huskihl]

So i checked the numbers with a ring and they look like they were right.

i also checked squish and it came in at 34 thousands. So if i delete the gasket it should drop the cyl 10-15 thousands to increase compression? Then i could raise the exhaust port to get in the 20 degree blowdown range?

Yeah. Make sure you check squish again. Gaskets are usually .017 - .020”ish

 

[Lightning Performance]

Why does 20 degrees blowdown seem to be a near perfect number for a lot of 70cc dual port transfer saws? I find it odd.

 

[JTV10]

So i pulled the base gasket and it measured 20 thousands.
Put the jug back on and got the following numbers,
Squish 18.5 thousands
Exhaust 103
Transfers 117
Intake 72

so for every 20 thousands i raise the exhaust roof i should gain roughly 2 degrees of blowdown. Or is my thinking flawed?

 

[huskihl]

So i pulled the base gasket and it measured 20 thousands.
Put the jug back on and got the following numbers,
Squish 18.5 thousands
Exhaust 103
Transfers 117
Intake 72

so for every 20 thousands i raise the exhaust roof i should gain roughly 2 degrees of blowdown. Or is my thinking flawed?

You’re close probably. I’d raise the ex to 99 and lower the intake to 78

 

[Redfin]

That ^ is exactly where I would set that jug.

 

[JTV10]

You’re close probably. I’d raise the ex to 99 and lower the intake to 78

my final numbers came out as,

Squish 19 thousands
Exhaust 99
Transfers 117
Intake 77.

Got it all back together and tuned it to 13000 wot. It was four stroking nicely and pulls the 24" chain with some nice grunt. After a couple of tanks I will lean it out.

Thank you Huskihl for the direction on the timing numbers they worked great.

 

[FergusonTO35]

Sure wish I could get some expensive saws that need p&c for free! 'Course, then I would end up just spending time and money on them.