MS 880 advice

[mtngun]

How big is the exit hole ? 1/2 inch ? I'd open it up, but that's just me.

I let it run at about 7900-8350. The chain was a bit grabby and would suck the rpms down to 6000 or less if I pushed at all.

How does that compare to your 084 ?

You've been milling for a long time, so I presume you have proven milling chains and a good feel for how a 120cc saw should perform.

After you have used the temperature probe for a while, please let us know what you think of it, and what you have learned.

 

[BobL]

How big is the exit hole ? 1/2 inch ? I'd open it up, but that's just me.

.

that muffler looks the same as mine. It's cast ally and the opening is 14 mm. I opened mine up to 19 mm. the saw breathes better and it seems to run better all round.

My full muffler mod is here.
http://www.arboristsite.com/showthread.php?t=88748

 

[billstuewe]

Excellent.

RE: Location:
there is a gap in the fins between the cylinder and exhaust manifold shown here.

It would be better if the naked sensor was embedded in a small block of ally and then inserted/jammed into that gap but insertion will be good enough for relative work. You can stick ir anywhere as long as you compare like with like. Don't worry it won't affect the cooling.

If it can reach I would put it inside rather than on the muffler but one would need to see if it and the insulation can handle the temperature first. I have a glass fibre insulated thermocouple than can check the actual internal muffler temp but currently I am nowhere near my home. I will check it out on the weekend.

Now that I have had time to read the directions and examine the prob/wires, it says to loop the wire all the way around the head (like a hangmans noose)and secure it around the inside of the last fin above the exhaust port where you point to on the picture. Is there enough wire to loop it around the head and still mount the sensor on the handlebar? The heat of the head won't melt the insullation on the wire?
It also says to mount it such that the sensor is located on the side of the saw, 90° to the exhaust port? And how did you mount the gauge to the saw? Velcro?
By the way, the saw IS running better and better. I emailed Stihl and got the following reply ref what RPM the saw would mill best at:

Dear Mr. Stuewe,



Thank you for contacting STIHL.



For the best performance from your STIHL MS 880, it is best to maintain the factory recommended carburetor settings for RPM. Operating this chainsaw at around the 7000 to 8000 RPM range under load should produce the best power, torque and provide adequate cooling. As your chainsaw gets more time on it, the engine will continue to break in and have even better power.



Thank you for using STIHL Products.



Regards,



Stuart Lumpkin

Technical Manager

Blue Mountain Equipment – STIHL

972-548-9045 Ext 104



Thanks,

 

[BobL]

Now that I have had time to read the directions and examine the prob/wires, it says to loop the wire all the way around the head (like a hangmans noose)and secure it around the inside of the last fin above the exhaust port where you point to on the picture. Is there enough wire to loop it around the head and still mount the sensor on the handlebar?

Unfortunately the wire loop is not long enough to do this.

The heat of the head won't melt the insullation on the wire?

The insulation appears to be some form of telfon which will remain solid up to a temperature of about 450F. If the outside of your head reaches this temp then the saw will be toast.

It also says to mount it such that the sensor is located on the side of the saw, 90° to the exhaust port?

This is suggested to give some average reading, but for chain saws we are more interested in the highest reading since it is the highest temps that cause problems. There are some temperature sensors that attach to the spark plug or replace the spark plug ring, but this is not the hottest part of the the engine which is somewhere in the the exhaust manifold or even into the exhaust where the combustion front reaches its max burn rate. This is why I decided to tuck the sensor inside the gap between the top of the exhaust manifold and the nearest fin. This is as close as I could get to the most temp sensitive part of engine, ie the top edge of the piston at the point where the exhaust gasses escape.

Ideally the sensor should be mounted inside the exhaust itself which would measure the temperature of the exhaust gasses and also make it suitable for tuning. There are exhaust gas temperature (EGT) sensors specifically designed to do this but they have fibreglass insulation because EGTs can reach over 1000F and this will definitely melt any teflon insulation.

To locate the Traax sensor outside the engine, one possibility is to drill a small hole in the exhaust manifold itself but I am still thinking about that. The other possibility is to embed it in a small ally block to jam in between two of the fins or between the the top of the exhaust manifold and the nearest fin. This would give a truer reading than doing what I have done because my sensor reading is affected by the cooling air generated by the fan. I don't think this really matters much since any external temperature sensor placement is a relative exercise anyway, so unless an EGT is used, the absolute temperatures don't mean much, it's the differences and changes that are important.

Here's how I cabled the sensor to the saw. I used a round file and made a 3/4 round notch in the base of the top plastic cover and then used one of the supplied pieces of silicone tubing to protect the wires at that crimping point. See arrow on LHS.

And how did you mount the gauge to the saw? Velcro?
The gauge is mounted to the same stand as my tacho stand described here.
I attached a piece of 1/16" ally plate to the stand underneath the tacho. The plate has a small offset to allow for the temp gauge to sit alongside the tacho. I just used a thick double sided tape but velcro would be better because if you leave the gauge on it will flatten the battery and then being able to take it off and remove the back of the gauge to replace the battery will be easier

By the way, the saw IS running better and better.

That's great.