Building a Milling Saw ms660 Clone for milling

[twalsh341]

Hello Everyone,
I'm building a NeoTech 660 clone into a milling saw, I had .050" squish, turned it down to .030" squish with gasket, My timing is Ex 95 Tf 124 In 80, giving 170* Ex duration and blowdown of 29*. Am I needing to get a different cylinder to get the exhaust/RPM to a safe level?

Thank you,
Trevor

 

[Maintenance supervisor]

Port brige looks cracked, get another cylinder.

 

[twalsh341]

Port brige looks cracked, get another cylinder.

It's not cracked, it's a blob of layout fluid.

 

[twalsh341]

Okay, so I needed some repair parts and got those installed. I've been having a bit of a time getting it to start and stay running. Today a landscaper who saw me getting frustrated came over and tuned the carb in a few minutes. When it's running it'll stay running at idle, although when I finished my first long slab cut it sat idling for about 1 minute, then stalled on it's own. After it cooled and I setup my next cut, refueled and oiled I had a bear getting it to restart. I got a couple pops, but no turnover.




The chain slows and stops if I lean on it. The saw doesn't slow, the clutch is slipping. I removed the chain brake band to see if maybe that was contributing to the hangup, but it still does it. Manual says it's either the brake band or worn clutch shoes or drum. Does the inside surface of the clutch need to be roughed up?

 

[J D]

I would be reluctant to mill anything until it's running as it should or you may end up having to start again with a new cylinder & piston.
Did you vac/pressure test it after you built it?
We're the parts all new?
What was your procedure for restarting it warm?
If it idles down & dies it could be a bit rich on the low side, if that's the case it should restart fine with a bit of throttle & will then smoke for a second.
Clutch/drum shouldn't need roughing up but I'd check they are clean (clean with brake parts cleaner).
Is it oiling well?
Does the chain move freely on the bar?
How is your chain sharpened? (Pic's would be good)

 

[twalsh341]

I would be reluctant to mill anything until it's running as it should or you may end up having to start again with a new cylinder & piston.
Did you vac/pressure test it after you built it?
We're the parts all new?
What was your procedure for restarting it warm?
If it idles down & dies it could be a bit rich on the low side, if that's the case it should restart fine with a bit of throttle & will then smoke for a second.
Clutch/drum shouldn't need roughing up but I'd check they are clean (clean with brake parts cleaner).
Is it oiling well?
Does the chain move freely on the bar?
How is your chain sharpened? (Pic's would be good)

I believe you, and agree with you and would tell anyone else exactly that. I was just plain too damn excited to not. I am running 32:1 (it might be a little bit oilier than this, and that is maybe also contributing to difficulty getting the carb set correctly because of a lot of oil in the mix?) and I did inspect the piston after a short run and no scoring. I'm also only on 3/4 throttle. My hope is that those things combined will have allowed me to make that cut without major damage.

I did not vac or pressure test it, I don't have a vac pump, I have a bike pump but hear that that's not a good way. It builds pressure when turned, and the decomp is pressurized, but I'm guessing that doesn't say anything about how MUCH pressure or whether there is a slow leak?

All parts are new, case and crank were per-assembled, I swapped out OEM flywheel key, throttle rod and have an OEM trigger and choke selector rod coming in. Bar is a new Forester.

For restarting warm, very soon after running (under a minuteish after shutoff) it will restart on ON, longer than that I've been setting it to the warm choke start. It seems to need the warm choke start, as that is also what has had more success starting it cold. If it popped two pulls I'd move it to ON.

"If it idles down & dies it could be a bit rich on the low side, if that's the case it should restart fine with a bit of throttle & will then smoke for a second." Now this seems likely, I believe this could be why it starts more reliably on the warm choke setting. If low is too rich, I want to tighten the L screw 1/16th turn at a time?

I will pull the clutch and clean it and the shoes well with solvent.

It oils well, I throws a good spray. I use veggie oil, chain moves freely and the groove and DL have a film of oil.

The chain is a Forester, full comp rip 3/8" .050 gauge. it's as is from the factory. I can snag a picture if needed.

 

[J D]

I toasted my first 390XP build by being hasty & over excited... It sticks with you when you have to re-replace an OEM top end for the sake of skipping a 10 minute test.
32:1 is fine... running at 3/4 throttle is not, especially for long cuts like milling!
You can do a pressure test with your bike pump, it just takes a bit more mucking around to make it work.

Yes, screwing the adjustment screws in will lean it up... I'd suggest doing some reading etc before just "having a go" as you can quickly toast a saw. Ideally get yourself a tach, set L & then set H to a few hundred RPM below max WOT RPM.
Madsens has a good tutorial, @Vintage Engine Repairs (Gaudoast) did one recently too.
Avoid storing the saw with any veg oil in it, it will gum up & become a huge headache. Might want to consider an aux oiler for milling too.
Is the chain still on the factory grind?

 

[twalsh341]

What is it about the 3/4 throttle that is worse that WOT? Does the lower speed keep the flywheel fan from moving as much air to cool the head?

I'll research how to to the pressure tests and post numbers when I'm able.

Chain is still factory grind, first cuts with it.

 

[J D]

Chainsaws are designed to run at idle or WOT. Consequently the carbs are designed to be tuned for these 2 states & during the transitional period in-between you get whatever mixture the combination of your tuning & the carb design ends up giving... which may very well be lean. Some saws/carbs are better/worse for this & at the end of the day if it's just transitional or for a short cut it's of no consequence. Definitely a consideration if you are making extended cuts like milling etc.
Additionally the amount of fuel flowing through the motor plays a significant role in cooling the engine (hence the recomendation to tune it a bit fat).
I know of carvers that have had major headaches when replacing saws as they can require them to work at part throttle for extended periods

 

[Mike Gudgeon]

Additionally the amount of fuel flowing through the motor plays a significant role in cooling the engine

Absolutely. And as JD also mentioned the mix isn't ideal at anything other than wide open so it gets lots of petrol/air mix. So, if you combine a bad petrogas mix with lack of cooling (by working at less than flat-out throttle) your saw will, sooner or later, spit the dummy because of it.
The same principle works for me with beer instead of petrol (though I have involuntarily ingested good amounts of petrol in my misspent youth)!

 

[twalsh341]

Chainsaws are designed to run at idle or WOT. Consequently the carbs are designed to be tuned for these 2 states & during the transitional period in-between you get whatever mixture the combination of your tuning & the carb design ends up giving... which may very well be lean. Some saws/carbs are better/worse for this & at the end of the day if it's just transitional or for a short cut it's of no consequence. Definitely a consideration if you are making extended cuts like milling etc.
Additionally the amount of fuel flowing through the motor plays a significant role in cooling the engine (hence the recomendation to tune it a bit fat).
I know of carvers that have had major headaches when replacing saws as they can require them to work at part throttle for extended periods

Could it be running so rich that it doesn't get full power, and the muffler runs hot because exhaust is igniting the extra fuel once it exits the cylinder?

 

[J D]

Could it be running so rich that it doesn't get full power, and the muffler runs hot because exhaust is igniting the extra fuel once it exits the cylinder?

Nope, if it's that rich it will smoke like a chimney & the excess fuel will further cool things. Fuel generally won't ignite in the muffler as there's not enough O2, if it did it would likely result in a less than ideal muffler mod