Need Help with Stihl 066 Rebuild

[NkyKelly]

I will start by saying I think that I have read every thread here and other sites regarding Chainsaw Rebuilds. Unfortunately, I seem to have some kind of mental block on understanding this or I have a unique problem. Either way I'm hoping you can help...

I have owned a Stihl 066 for 16 years. I purchased it as a Powerhead (without Bar/Chain) for a Chainsaw mill. I really haven't used it much, but I did get a 20" bar for it to use for Yard and Farm projects. I had actually written a long version of this, but decided not to bore anyone and turned it into as shortest of a bulleted list as possible.

Still a long story..

• In late April I used the saw to prepare some logs for milling. Used saw on and off for 4 hours running a tank and half through it. Saw some smoke at the end, but all seemed good and did not really notice power drop until very end. Chain was dull so I quit for the day.
• Next day, saw wouldn't start. Compression was low, but not gone. Took to Stihl Dealer and disovered burnt up Piston and Cylinder. You could see the scorching through exhaust port.
• Dealer said it wasn't worth repairing, but while searching to see what the used parts were worth on eBay, I discovered Asian made replacement parts for it. So I ordered a Big Bore Cylinder, Piston, Rings and Gasket set from a guy in the states.
• Did the rebuild and everything looked good. Saw started right up, but it didn't idle well. I didn't adjust anything, but I did follow some basic break-in procedures that I read here and other places. Ran half-tank of rich 35/1 mix. Ran for 15-20 minutes never going above 75%-80% throttle. All seemed good.
• The next day it started right up and I proceeded to run it much harder. Ran off and on for 2 or 3 hours using about 3/4 of a tank (35/1 mix). Saw started everytime, but didn't idle well. Chain was not bad, but not great. At one point, I noticed that the it was really losing power. I had to go to family event so I left the saw to cool.
• When I got back to the saw the next day, the saw was hard to start and did not run well enough to use. I removed the muffler and discovered another scorhced/burnt piston.
• I realized that I was stupid. I didn't even investigate what might have caused the original failure. Once I read things on the web, I realized leaving everything the same was very very stupid. Afterall, something caused the original problem and I knew it wasn't Straight Fuel since I was the one that was using it.
• The vendor was great. When I gave him my honest story and asked about a discount on replacement he replaced them as warranty. He even gave some advice as to usual causes and threw-in a new intake boot.
• I completed the 2nd rebuild over the weekend. This time I finished by doing some basic pressure testing (Poor Man's version) and all seemed good. I really focused on making sure all gaskets, boots and hoses were good. Based on what I have seen, the pressure test was positive. I put the Carb back on and the saw back together.
• I adjusted the Carb using techniques here and around the web. Once I had it good, I set the High Adjustment 1/4 turn Rich to be safe.
• The saw was running great last night and I proceeded to make a finish a cut on a stump.I didn't run it much, but it sure seems like the Cyclinder and Muffler is getting extremely hot.
• I don't think I burned anything up, but now I'm scared to run it. I certainly don't want to put it on the Chainsaw Mill because that runs the saw harder than anything. Of course, the Chainsaw Mill is my whole reason for wanting this running so I am bummed out.

So, where do I go from here? I have rebuilt a two-cylinder Jet Ski motor without an issue, but this thing has me stumped. Its just way too sensitive. Based on what I read, an issue that causes this kind of destruction with just a tank of Gas should be very big and easy to find.

Am I missing something or just being stupid? Is there a way to know whether it is in fact running too hot before its too late and I simply burn up another top-end

I have read threads telling other people to send their saw to one of the guys here and have it "gone-threw". Who does that and what does it costs. I think I have the parts already, would someone be willing to use the parts I have already. Heck, I even have another Cylinder and Piston set that I ordered from Hong Kong originally. (Took 30 days to get here).

I simply just don't want to keep doing this to myself. I want to get to milling and focus on my woodworking.

Thanks,
Kelly

 

[mdavlee]

Are the carb limiters gone? If they are start at 1.25 turns out on both. The idle should be able to be stable. If the chain turns at idle then you've got worn utch springs or an air leak.

 

[surfincr]

when you rebuilt the saw did you ever replace the oil seals? i've found in the past especially on old saws when i'm rebuilding them its worth the extra time and money to throw new seals in

 

[gunnusmc03]

Did you only pressure test? Did your test include vacuum test as well?

 

[NkyKelly]

when you rebuilt the saw did you ever replace the oil seals? i've found in the past especially on old saws when i'm rebuilding them its worth the extra time and money to throw new seals in

I did not replace any seals. By Oil Seals do you mean on the crank bearings? I could do that, but it does take the job to a whole other level. Top-End rebuild very different than from pulling apart the bottom for me. Does it need to come completely apart or are the seals done from the outside?

 

[BuckthornBonnie]

Agreed... go even further than that and just replace all rubber parts (fuel related) including seals, fuel line, fuel filter, impulse line, and the usual carb stuff. The vaccuum test should indicate seal problems.
Some air leaks are obvious, others are hidden and appear during different run conditions. If you're still having trouble, bring it to another/honest shop (not necessarily a Stihl dealer) to get an opinion.
Remove clutch drum and grab the crank and give it a good wiggle... any play? If so, then you have bottom end issues. Grab the flywheel and try to rock it in different directions... any play? See above. Case split/bearing install isn't the end of a saw, but it's often the end of the line for many people that start rebuilds.

 

[NkyKelly]

Are the carb limiters gone? If they are start at 1.25 turns out on both. The idle should be able to be stable. If the chain turns at idle then you've got worn utch springs or an air leak.

Not sure what Carb Limiters are, but if they limit the screw travel then NO. I think the total turn possible is less than 1 full turn from totally IN. I did notice that I was unable to adjust it to the point it smoked. It gurgled a little and I think I'm just in from where it gurgled at High Speed. I'm a bit nervous running it long enough at High to adjust the High Speed. I getting ready to order a Stihl Tachometer from ebay vendor, so I'm hoping using RPM-based guide will help me get this perfect. That will be useful for the future anyway.

After the last rebuild, the Idle was adjust so it stays running, but chain does not move.

thanks for the reply.

 

[surfincr]

I did not replace any seals. By Oil Seals do you mean on the crank bearings? I could do that, but it does take the job to a whole other level. Top-End rebuild very different than from pulling apart the bottom for me. Does it need to come completely apart or are the seals done from the outside?

those are the ones, when i first started out i never replaced them since i thought it was way too hard, then i bought a generic stihl flywheel puller which made it a piece of cake. you dont need to split the case at all, just pull the covers pull the clutch, and if you want to be safe remove the oiler. a lot of folks on here use a dry wall screw to screw into the seal then pull with pliers. on the other side just pull the flywheel and the seal is right there. each of the saws i have had to do the seals on it seems to always be the flywheel side but for piece of mind its easy enough to do both sides.

 

[gunnusmc03]

If you pull out the carb grommet you can quickly tell if the carb has limiters. They'll be little red caps that cover the low and high speed adjustment screws. If you can only turn the high speed out 1 turn max it sounds limited.

Was the saw 4 stroking out of the cut when you were tuning it?

 

[blsnelling]

You only have to remove the flywheel, clutch, and oil pump to replace the crank seals. If you haven't yet done a vac test, that is mandatory. You don't necessarily need to replace all the other rubber parts, but they should all be removed and closely inspected. The carb should be cleaned and a OEM kit installed.

 

[NkyKelly]

Did you only pressure test? Did your test include vacuum test as well?

I did just Pressure Test. I have no equipment for Vacuum test. As I understand it, an air leak that causes this quick of a fail (less than a tank) is going to be seen on both Pressure and Vacuum test. Is that not the case?

 

[BuckthornBonnie]

You only have to remove the flywheel, clutch, and oil pump to replace the crank seals. If you haven't yet done a vac test, that is mandatory. You don't necessarily need to replace all the other rubber parts, but they should all be removed and closely inspected. The carb should be cleaned and a OEM kit installed.

With any luck most of the rubber will check out "ok," but it can be easy to overlook the actual crack on a fuel or impulse line. I'd suspect the seals, though, based on the above description. The dang smalls add up quickly on a rebuild, but I don't mind the added insurance of all new. Good thing about 2-strokes, there aren't too many places that can leak air and most are easily accessible as Brad mentioned above. Good luck!

 

[gunnusmc03]

I did just Pressure Test. I have no equipment for Vacuum test. As I understand it, an air leak that causes this quick of a fail (less than a tank) is going to be seen on both Pressure and Vacuum test. Is that not the case?

Sometimes it will pass pressure but fail the vac test.

 

[NkyKelly]

If you pull out the carb grommet you can quickly tell if the carb has limiters. They'll be little red caps that cover the low and high speed adjustment screws. If you can only turn the high speed out 1 turn max it sounds limited.

Was the saw 4 stroking out of the cut when you were tuning it?

Correct, I had it apart so I know the Red Caps are on there. Didn't know those were limiters. Since it seem to run fine, I tried to avoid a Carb Rebuild. I can understand it getting too rich and needing to be adjusted in with Age, but I didn't think it would change so that I couldn't adjust the lean. Of course, like I said, it definitely can't be adjusted rich enough to get it to smoke like some of the tuning guides say.

Not sure what "4 stroking" is but I have heard that term before. I'm a fairly handy guy and have rebuilt a few things, but maybe I'm in over my head. I simply let the saw warm up a bit and tuned it on the Bench. Since I was trying to play it safe, I basically adjusted the H Speed adjustment to just a bit from all the way out. With the limiters, that seems like it is going to be around 3/4 of a turn.

 

[lone wolf]

I did just Pressure Test. I have no equipment for Vacuum test. As I understand it, an air leak that causes this quick of a fail (less than a tank) is going to be seen on both Pressure and Vacuum test. Is that not the case?

A bad crank seal can and often will pass pressure but fail a vac test. Believe it or not.

 

[NkyKelly]

With any luck most of the rubber will check out "ok," but it can be easy to overlook the actual crack on a fuel or impulse line. I'd suspect the seals, though, based on the above description. The dang smalls add up quickly on a rebuild, but I don't mind the added insurance of all new. Good thing about 2-strokes, there aren't too many places that can leak air and most are easily accessible as Brad mentioned above. Good luck!

You only have to remove the flywheel, clutch, and oil pump to replace the crank seals. If you haven't yet done a vac test, that is mandatory. You don't necessarily need to replace all the other rubber parts, but they should all be removed and closely inspected. The carb should be cleaned and a OEM kit installed.

Thanks. I didn't catch the first one Bonnie until blsnelling posted a reply to it.

I did have the clutch and oiler off and could see the seals. They just didn't look replaceable from the outside and since I didn't have replacements, I didnt try to pop them out.

Thanks to everyone for all the replies. I really just want to get my Chainsaw Mill going and I'm losing patience with this stuff. So it helps to talk with others. If I had the money, I would already own a new or slightly used power head. I love messing with these things, but only when I have no other pressures or the need to have it so I can complete something else. I had my Jet Ski Motor on the bench of a couple of weeks and thoroughly enjoyed it and was very successful at rebuilding first try. Even did some DIY porting and modding of the exhaust.

So far, I am unable to find a Local person that I trust that is willing to work on it. Find a couple of guys on Craigslist, but they want to trade my saw out for a smaller husky and a little bit of cash. As I remember, even at 92+CCs this thing was a bit underpowered on a decent sized log.

 

[NkyKelly]

By the way, I need to purchase the Service Guide. I have done all this using the only Stihl Service Guide I could find for free on the web. it wasn't for this model. I know, $1000 powerhead and I'm worried about $20.

 

[NkyKelly]

A bad crank seal can and often will pass pressure but fail a vac test. Believe it or not.

I will believe anything because I don't know any better. There is a crap load of misinformation out there.

I guess I could try to do the Vac test with the breakline tool from Harbor freight. One of the reasons I didn't was because I wouldn't know what is acceptable. Like how much leak down should there be and what is acceptable.

 

[drf255]

Do you have the old jug? May still be usable.

Maybe someone here will help you out with the work.

Problem you have is in the price at this point. AM big bores make less power than OEM standard bore. You could buy a used 066 for $700-800, maybe less as its a buyers market right now.. Sell yours for $300-400 in the fall as is.

Or pay $300-400 for parts and repairs to yours and be down for some time. The amounts add up really quick when rebuilding a saw.

 

[Rookie1]

Lots to read,maybe i missed it, but did you take carb apart and check condition of it? BIL burned up 026 because the screen in the carb was plugging up and ran lean. He put new cylinder and piston on and got replacement carb now saw is back to normal. I may look into buying new carb from Stihl dealer.