Compression Dropoff stihl 066

[DonE911]

For some of you guys who actually wear out saws....

One of my 066's I use to mill with is starting to feel tierd as compared with the other one....   I check compression and it was 138 (ish) lbs.... I checked it a few months ago and it was about 150lbs....  should compression number fall that fast....  its only seen about 1 gal of fuel in that time....   everything as far as fuel/oil clean filters ect has been done (always).  The other saw has seen about the same use and the numbers have stayed the same.

Anyone know what the cost for new piston/cyl are for these saws?  I'll have to start a fund for it soon.

Thanks in advance

[Minnesota_boy]

No, compression shouldn't drop off that fast.  Pull the muffler and check the piston for signs of scoring. Also look for buildup of carbon deposits in the exhaust outlet.  The two could be related.

[Timburr]

In my experience, when a saw starts to lose compression, it loses it comparatively quickly....the greater the running clearances, the quicker the wear (a disproportionate ratio).... although 1 gall. of fuel is a bit too quick.
A piston/ barrel combo. is about half the cost of a new saw and I personally chuck a saw when it's worn out. Even with a new piston/cylinder, the crank bearings/seals and carburettor will show wear and it is false economy not to give these attention.....costs mount up even more.
I have had joy by replacing just the piston though, as long as the cylinder is honed first. This was meant to be a tempory repair, but is still going strong two years later.

[oldschoolmiller]

Here is a kit on e-bay, it should save you a few bucks, it is brand new and runs about $210 if i remeber correctly, it has been my experience that when a milling saw starts to go, it goes quick  :'(

eBay link

[DonE911]

oldschool,

Thanks for the link.....   thats quite a bit cheaper than the new saw route.  I've replaced the top end on other saws and they are still running great, no bottom end problems.....   does the milling process wear out the bottom end more so then say cutting firewood??  In your opinion will the bottom end last another top? ( if properly cared for ofcourse )

[Timburr]

DonE

Most modern saws have a robust bottom end and will outlast the topend 4:1.....I'll clarify - it is the topend that will fail 4 times out of 5, not that the bottom-end lasts 4 times longer. I'm talking about saws from new.

I guess milling must put extra strain on the crank journals, because the engine is under full load for longer.....firewooding is continually on load and off load, giving it a 'resting' period. This resting period helps bring engine temps to an equillibrium with fewer hotspots.

There's no denying, milling is hard on chainsaws, but as long as the crank is receiving adequate oil by keeping fuel mixture on the generous side, it increases your chances of everything staying together.

I was taught to tune the mixtures to their correct setting, and then unscrew each one out by 1/8 turn.This richens the mixture slightly and consequently gives it a tad more oil. My oil/fuel mix is 15% higher than manufacturer's spec..insurance eh!

[DonE911]

thats good news ..... 

I run 40:1 instead of 50:1 and do run it at a slightly rich setting.

I'll start sav'n for a couple new top ends... 


I pulled the muffler and everything looks fine... so I guess its just starting to wear out.  I'll start doing a compression check everytime I use it.  Maybe I'll learn somfin

[low_48]

I'm trying to remember the details on the 066 leaning out. I bought an 066 on Ebay that would not start. I took it to the dealer and he told me it did not have enough compression to start. Here's the part I don't exactly remember, he told me about a part in the carb (maybe a valve) that was breaking down with time, just on the 066. This caused it to lean out and burn up the cylinder. He said that if you felt like the saw was REALLY running well, felt like it had extra power, it could then be on it's way out. Get the carb rebuilt ASAP! I was able to return the saw, but had to go through negotiation. Cost me about $120 to learn not to buy a used saw on Ebay. :-[

[DonE911]

This saw is an ebay saw ...  I've had it for a while though and no problems.  Sorry to hear about your bad luck on ebay.

I ran another gallon thru it today... no change in the comp numbers...  If it doesn't rain all day again I'll probably run another gallon thru it tomorrow... still got a few oak logs to mill.

I'm starting to wonder if maybe I just checked comp on the other saw twice instead of once on each. I've done stupid things like that before....  maybe the saw has had 4 or 5 gallons thru it instead of one.  I think tomorrow I will get out the sharpie and mark them better just to be sure.

[DonE911]

 >:( >:( >:( >:(

Just to update this thread.....  I found the problem...   it was the stupid operator

He didn't bother to clean around the spark plug seat... didn't get a good seal... everything is fine.

As for the feeling tired??  The stupid operator (me) used both saws and they feel about the same.