Author Topic: 4000 rpm's  (Read 579 times)

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Offline fossil

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Re: 4000 rpm's
« Reply #10 on: January 30, 2014, 05:34:33 pm »
Roger,

If you ever pull the cylinder off that 3700 I sure would like a few pics of the intake and exhaust ports.
Tim

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Re: 4000 rpm's
« Reply #11 on: January 30, 2014, 06:45:05 pm »
Roger,

If you ever pull the cylinder off that 3700 I sure would like a few pics of the intake and exhaust ports.

Will do Tim.   I have another one here that is a 3700 but is a craftsman in red.  I am going to do it also.   When I do I will take some pictures.
PP 505, 475, 445.

Offline redunshee

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Re: 4000 rpm's
« Reply #12 on: January 30, 2014, 08:13:48 pm »
Roger,

If you ever pull the cylinder off that 3700 I sure would like a few pics of the intake and exhaust ports.

I've got two 3700 cylinders that have different exhaust port sizes.  One exhaust port looks exactly like a 3400 i.e. There is a slight ridge on the exterior of the port.  The other cylinder has the ridge removed and is open much more.  I thought all 3700's were like the latter one as opposed to the 3400 type. Think I'll pull the mufflers off my two 3700 saws and look at the exhaust ports.

Offline redunshee

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Re: 4000 rpm's
« Reply #13 on: January 30, 2014, 08:15:35 pm »
Roger,

If you ever pull the cylinder off that 3700 I sure would like a few pics of the intake and exhaust ports.

Will do Tim.   I have another one here that is a 3700 but is a craftsman in red.  I am going to do it also.   When I do I will take some pictures.

Roger, are the red Craftsman 3.7 ,  3800's with plain bore and aluminum piston with thick rings?

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Re: 4000 rpm's
« Reply #14 on: January 30, 2014, 08:55:35 pm »
This particular one is the two thin ring chrome bore 3700.    The red ones came both ways.


Bob let us know what you find on your other 3700 exhaust ports.
PP 505, 475, 445.

Offline Al Smith

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Re: 4000 rpm's
« Reply #15 on: January 30, 2014, 09:18:34 pm »
You'd be surprised what you can crank them up to and they run forever .One of many reasons I'm a proponent of heavier oil mix gas .

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Re: 4000 rpm's
« Reply #16 on: January 30, 2014, 09:23:47 pm »
You'd be surprised what you can crank them up to and they run forever .One of many reasons I'm a proponent of heavier oil mix gas .


I agree Al and I changed from 40 to 1 to 32 to 1.   
PP 505, 475, 445.

Offline moparman texas

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Re: 4000 rpm's
« Reply #17 on: February 03, 2014, 11:00:53 pm »
The needle bearings are the weak link in this series of saws, plus the powder metal crankshaft is weak and heavy. If you run these engines at 13000 plus for any length of time, they will come apart.
The only thing that you accomplish by running 32:1 in these engines is to carbon up the engines, stick the rings, and create smoke. The very slight increase in lubrication over 40:1 or 50:1 will not make any significant improvement in needle bearing life - the needle bearings just can not handle rpm like ball bearings. Virtually any engine made from circa 1980 to present date have engine components that will run better and have equal life with 40:1 or 50:1 when compared to 32:1.
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Offline Eccentric

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Re: 4000 rpm's
« Reply #18 on: February 03, 2014, 11:42:16 pm »
I don't get any significant carbon buildup, ring sticking, or smoke from running Redline Race Synthetic (or Stihl Ultra or Woodland Pro Synthetic) at 32/1.  Been running 32/1 with good synthetic in all my 2-stroke equipment for decades without issues. 

Back when I switched from 50/1 to 32/1 I saw an increase of residual oil on internal engine parts, but no increase in carbon.  Also, some saws (such as the 365/372 and 385/390 Huskys) have much better bearing life at 32/1 than at 50/1 in logging conditions.  Yes I realize those saws have ball bearings vs the needle bearings in the 3400-4000 CounterVibes.  I don't wind my CounterVibes up at stratospheric RPM levels............but I'm also not sticking rings in those saws with a 32/1 mix. 

Why is it that going from 2% to 3.125% oil will on one hand not give a significant increase of lubrication.......................while at the same time cause a drastic increase in carbon deposits, smoke, and related issues?  I think this is another case of agreeing to disagree....
-Aaron

For older saws:
Tune the H side so that it 4-strokes (burbles) at WOT unloaded and just cleans up when under load.
When you lift cutting load, the saw should immediately revert to 4-stroking.  Fine tune the transition point for the wood you're cutting.
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Re: 4000 rpm's
« Reply #19 on: February 03, 2014, 11:46:52 pm »
I will take my chances with my 3700 turning 13000 rpm's.    With 40 something saws to use I do not think it will get over used.   Besides in the cut it is probably only turning around 9000 rpm's.
PP 505, 475, 445.
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