660 racing out of control

Timberguytim · December 24, 2019, 03:37:23 PM

I am a veteran operator as well as full time marine mechanic. This problem came on slowly and continuously got worse. Now the saw will not idle at all. It was purchased in the Philippines and is a German made Stihl. It has no restrictions on carburetor adjustments. Both high and low speed needle have always been at about 1.5 turns open. The saw is about 12 years old but sat on the shelf the last 5 years. I started with clutch side crankshaft seal then intake snorkel, pulse tube, carburetor kit all to no avail. All above mentioned parts were pristine. Saw has NEVER tasted ethanol (have to be very careful here as MN is one of the mandated states. Does anyone have the nerve to recommend another option to repair? Could it be flywheel side seal? I have an 064 with never a problem, also an 084 and poppa 880 magnum. Never "saw" this problem with a Stihl.

sawguy21 · December 24, 2019, 03:47:51 PM

Welcome!! Grab a coffee and pull up a stump. Those are classic signs of an intake air leak, the crankcase needs to be pressure tested which is quicker and easier than randomly changing parts.

Al_Smith · December 24, 2019, 07:21:16 PM

It's a leak some place .Although it would be highly unlikely it could be a case or cylinder base gasket leak if it's not a crankshaft seal .

Mad Professor · December 24, 2019, 08:07:16 PM

You want to test for leaks under pressure and vacuum.

If you don't have a pump, a Mitivac 8500 will do both, ~$70.

Stihl gasket sets come with seals and cost less than just buying seals.

If you work on stihls the flywheel puller is a good investment too.

Timberguytim · December 25, 2019, 01:49:08 AM

Thanks a million for these responses. I do have a flywheel puller for this saw. The problem came on slowly. Does anyone here see this before on the Stihls? What usually fails? Had a Johnny 90 that developed vac leak too. Kept running it until it started to knock, so I put it on the shelf and bought a 999 Oly. Sweet saws.....made in Italy. It's an animal. Used it for 10 years cutting ice for resorts in Canada. Ice requires a lot of power. Now where's my coffee?

luap · December 25, 2019, 01:52:39 PM

Quick and easy check that the head/cylinder bolts are tight.

Northeaster · January 05, 2020, 08:13:28 PM

I am new to this forum, but just had similar issues on an 064 that i bought used. When i admitted to myslelf that I needed to find the source, or risk damage soon.. i bought a cheap pressure/ vacuum pump and it ends up being the flywheel side seal.. worse really, as when I bought it a few months (and little use) earlier i couldn't feel any play in either crank bearing, but now there was play in the flywheel side.. i knew it wouldn't work...but in denial, i replaced only the seal and it started and idled well..for short period... of course, the new seal didn't last long with a bad bearing. so now i habve replaced both bearings and seals and while i had it apart cleaned up the OEM piston and cylinder, replaced the rings and now she seems fine...
I bought this cheap pump - not as rugged as the Mightyvac but ok for the money - kit and attachments cheap.. no affiliation..
https://www.amazon.ca/8milelake-Vacuum-Pressure-Bleeder-Bleeding/dp/B0727Z9B79/ref=sr_1_5?keywords=vacuum+pressure+pumps&qid=1578273160&sr=8-5

mine was from a different vendor but unit looks the same.
fyi - my seal looked fine but leaked under pressure and vacuum when tested.. easy to spot bubbles/ soapy water under pressure. leak was so bad i needed someone to pump while i looked as it wouldnt hold pressure at all.

Timberguytim · January 06, 2020, 03:03:09 PM

Thanks, my friend. Excellent information. Also have an 064 but it's on the shelf with another issue. Gonna pull flywheel and pressure test. I have a converted unit that I use for radiators and lower units as well. Can pump to 40 psi.

Timberguytim · January 24, 2020, 12:19:10 AM

Okay finally got to the 660. Put output side of small shop vac into carb with throttle open. Enough pressure getting to crankcase to discover this "bubble bath" at base of jug. Ran it for probably 2 semi loads worth of dicing red oak with certain idle speed issues. Finally idle became "non-existant". Started using the other saws for last 3 years. Bought this baby in the Philippines in 2004 or 2005. Hundreds and hundreds of hours bucking mostly red oak at 17". 404 full chisel Stihl chain with 20" bar. Amazing thing is.....look at that piston, look at that exhaust. This is Philippines market saw, spark arrestor delete, no restriction to adjusting mixture screws, running lean for hundreds of hours. THIS is why I burn Amsoil synthetic at 64:1. Before Saber came out maybe 4 years ago, I used Outboard 100:1 pre-mix but mixed 64:1 with non oxy fuel only. There is NO CARBON anywhere. These muffler and port photos are unedited with NO cleaning whatsoever. If anyone can show me a sweeter piston, rings, and cylinder on a saw with this many hours, working year round in Northern Minnesota, besides with jug gasket causing lean burn.......I will abandon my Amsoil and start "smokin' " it up at 40 or 50:1 on YOUR oil.

Timberguytim · January 24, 2020, 11:04:22 AM

Picture of problem.

Timberguytim · January 24, 2020, 06:05:32 PM

Trouble loading photos. Check out this muffler.

Mountain_d · January 26, 2020, 08:07:41 AM

When doing the vacuum / pressure leak test, what is the easiest way to block the exhaust and intake ports?
Mountain

Timberguytim · January 26, 2020, 07:03:16 PM

I just had piston up and very little air escaped through exhaust. Carb was fitted in place with 2 nuts but without air filter mount in place so it was easy to supply plenty of air by just holding flexible vacuum nozzle up to carb with pressure side of vacuum. No bubbling at case, crank seals, or intake manifold, but major leak at jug base gasket under the muffler.....see picture. This gasket failure happened over a few months as I was dicing a couple semi loads of oak.

sawguy21 · January 26, 2020, 07:57:59 PM

@Mountain_d the Miteyvac tester covers the intake side secured by the air box nuts. Cut a piece of gasket material to cover the exhaust port and secure it with the muffler.

Timberguytim · January 26, 2020, 11:59:36 PM

Great idea, thanks. I really see no reason for this failure. Lost a little faith in Stihl here. I baby my saws. This piston and cylinder absolutely like new. 8 years use at about 75 cords (loggers) average per year bucked to 16 to 17.5" pieces dry barkless red and white oak, sugar maple, little Birch and black Ash. Amsoil 100:1 Outboard pre mix @ 64:1 with non oxy 91 octane. Now just try to change my mind on oil.

sawguy21 · January 27, 2020, 12:50:59 AM

Don't be hard on Stihl, 75 cords a year over 8 years is a lot of cutting! It's a machine, they don't run forever. Be glad it is an inexpensive and relatively easy fix.

Timberguytim · January 27, 2020, 01:00:36 AM

Yes Stihl is Stihl my favorite, but question this gasket. Bolts were tight, surfaces look good.

sawguy21 · January 27, 2020, 11:34:14 AM

You couuld machine the cylinder and use a thicker gasket but is it worth the time and money. Put it together and get back to work. ;)

Timberguytim · January 27, 2020, 07:14:45 PM

Think I'm gonna give it a little high temp anaerobic.....I use Loctite 518 on outboards and its tested to 300F. What do you think? You can see that the original gasket "slid" out of place. In reality, I was "blindsided" by this failure. I originally bought the saw because of the higher power and "inboard" clutch with intention to use for cutting ice up in remote Ontario for refrigeration. My 999 Olympic has an exposed clutch and collects too much water, then beginning to slip. More power than the 660 but slow cutting once you break through to the water. I found out the 660 was shy of power so my wife bought an 880 magnum.....in board clutch. The power is practically addictive so I've been running it in the heavy oak. Its surely not a saw for the timid, but now the spark died. I have to get a new coil, so stepped back to the 044 AV and the 925 Homelite until I get these Stihls running. I will someday break out my Asian market 08 which is still in the box. Just over 100cc, had to leave the bar in Philippines. These saws are assembled in China around the OEM Stihl powerhead. All the outer dress is China made with bigger tanks and a bit less "perfect" fits. They are used primarily in the Philippines for free cutting coconut lumber which is brutal work. Paid the equivalent of $650 USD....brand new with German 36" bar and Stihl .404 semi chisel. This saw certainly has the torque to tear up 3/8" equipment when making lumber from hardwoods of the south pacific.

ZeroJunk · January 27, 2020, 09:30:29 PM

If that is supposed to be a MS660 gasket it is not OEM. They went to metal gaskets in those size saws a long time ago.

Well, let me re phrase that. They actually show one on the IPL. But, I have been in a bunch of them and have never seen one.

So, when you rebuild it get the metal gasket.

Timberguytim · January 27, 2020, 09:46:45 PM

Thanks, any suggestions about sealant? Additionally I know that the saws destined for the Asian markets are often made slightly different because of EPA requirements, eh? Perhaps this gasket slightly thicker or thinner than the steel formulation gasket.

sawguy21 · January 28, 2020, 11:30:05 AM

As long as the mating surfaces are clean there is no need for sealant.

Timberguytim · January 28, 2020, 03:38:11 PM

It is surprising to me that sucking in dust and dry air for all that time didn't ruin the saw. My stupidity to continue operating it was trumped by my choice of oil. Even in the Philippines this saw cost me well over $1,000 bucks in about 2006.