Stihl 075 Complete Rebuild and Performance Mods

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Your original cup is not salvageable? It doesn't look all that bad in the pic.
It can be salvaged. Just a bit more wear than I would prefer. I went rooting through my parts stash and found a really nice one, along with the plastic ring. Just need to have a few in reserve because I have several more 075's to do. I could swap to the 076 pawl style, but that requires the 076 flywheel and starter bits, too.

Speaking of parts, while I was looking for the starter cup, I pulled out my extra pistons, inventoried the extra jugs, checked mufflers, and grabbed my full wrap specific bits for the handlebar. I'm in good shape on pistons -- have 4 to choose from -- NOS, almost new, nice used, and an ok used one. Will probably go with almost new. The jug on this saw is nice, but it looks like I have 5 spares for the rest of my saws. I have about 5 mufflers to choose from, but one is homemade and two are aftermarket. I think I have two that would force me to use the 1/2" spacers on the muffler guard and one that wouldn't. I also have bits to do at least the full wrap on this saw, but then I run out of the hard to find handlebar mounts and AV rubber.
 
Comparing mufflers here; have what appears to be 075/076 mufflers, but one is wider. As I understand it, the wider muffler is a U.S. only model, and the standard muffler cover won't fit over it, so you have to use 1/2" spacers and longer screws to mount it. This saw came with the smaller muffler, so that's what I'm going to use. I resisted the urge to blast it and paint it hi-temp flat black, but I did clean up some of the exit where it was a bit jagged and uneven.

I have an 051 muffler somewhere in one of my boxes; would have been nice to have one to compare, but I didn't want to spend 30 minutes digging through my stuff to find it.

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Got a bit more done after work today. I cleaned the carbon off the very lightly used piston and mounted it on the rod so I could check piston to cylinder clearance. I checked with no base gasket and it was tighter than I expected at .012". No chance of doing a base gasket delete.

My technique - use thin solder wire held into place with a dab of grease, install jug, rotate several times, remove jug, measure solder with calipers.

I then checked the thickness of the base gasket and it was .008, so all I have to do is use it for perfect clearance of .020". It doesn't usually work out like this, but I'm not complaining.

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Wasn't happy with how intake gaskets and carburetor heat shield protruded into the intake port so I did some minor grinding and trimming.
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Noticed that the case I was using was a bit different than the case that the parts came from. It has an extra threaded boss for the later style muffler guard to attach. I ended up using a spare muffler guard that I had that had matching paint and patina.
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Here you can see three different muffler guards that I had in my stash. I'm not sure if there are other variations out there.
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Fuel tank and starter assembly ready to reinstall.

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Starting to look like a saw again now.

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Got it all back together and then the fun started....

When I pulled the starter handle, the cord wouldn't rewind. No big deal; I installed the pawl and spring assembly upside down. Easy enough to fix.

Then it turned over fine, but made a helluva racket. I knew what the sound was immediately -- noisy crank bearings. When I removed them, they felt a bit gritty, but I thought it was just some carbon and grit that needed to be cleaned out. They felt good when cleaned and oiled so I reinstalled them. Dumb move. New bearings are only about $20 for a set ($90 if you buy NOS Stihl) but I didn't have any handy when the saw was coming back together. So it has to come back apart to install a set of new SKF bearings. Fook.

Also checked for spark and didn't see any. Shite. I have a few extra coils, trigger units, etc, so I can swap stuff around if needed.

To add insult to injury, there was an 076 that just sold on eBay over the weekend for $660. Seemed to be in similar condition to the 076 that sold for $1525 a few weeks ago; only difference was this one was a Super. Is a Super really worth more than twice what a regular 075/076 is?
 
None of em are worth that in my opinion -- unless very nicely restored.

And let's hope the retainers didn't let loose in those bearings creating additional damage.

It certainly didn't sound/feel like anything got loose. More of a consistent sound than the sound of something coming off and getting crushed.
 
fun fact...roller bearings are chrome plated and it likes to chip off if anything gets in there. I see it all the time in wheel bearings/ trailer bearings/differential bearings, and pulley bearings..if they feel even a hair gritty after cleaning they go into the trash, even if they look good!
 
roller bearings are chrome plated

You'd be very hard pressed to find chrome plating used in/on any bearing. That said, chrome is commonly used in the various alloy compositions of the steel itself, but not as a surface plating. SAE 52100 Chrome Steel is the most common material used in the manufacture of precision bearings.

https://www.astbearings.com/bearing-materials.html
 
SKF bearings will be here today. Time to disassemble again.

How do y'all heat up your cases to drop bearings in? In the oven or using a heat gun? I'm not sure my heat gun gets things hot enough to make that much of a difference. I'm also freezing the bearings, of course.
 
Never had much luck with a heat gun. I have a small toaster oven that heats to approximately 450 degrees and is just big enough for most case halves. When you heat, get it hotter than you think you need to for a better chance of success. 350 ~ 400 will usually do the trick without even freezing the bearing. That's also how to get bearings out of a case. Heat to around 400F and they'll drop right out.

On the other hand for installation, my last several bearing installations were simply done with a bolt, a nut, and washers to just draw the bearing into position vs. using a press (which is also a common method in some circles). Using the correct size washer puts equal pressure on both the inner and outer races and eliminates the possibility of any axial flex. Very effective and economical approach.
 
Never had much luck with a heat gun. I have a small toaster oven that heats to approximately 450 degrees and is just big enough for most case halves. When you heat, get it hotter than you think you need to for a better chance of success. 350 ~ 400 will usually do the trick without even freezing the bearing. That's also how to get bearings out of a case. Heat to around 400F and they'll drop right out.

On the other hand for installation, my last several bearing installations were simply done with a bolt, a nut, and washers to just draw the bearing into position vs. using a press (which is also a common method in some circles). Using the correct size washer puts equal pressure on both the inner and outer races and eliminates the possibility of any axial flex. Very effective and economical approach.

Never had any issue getting them out. Usually hit them with Kroil to loosen 'em up a bit and then tap out with a ball peen and appropriately sized socket.

I have a 12 ton shop press in the garage, but haven't ever tried it for chainsaw stuff. I think I'd be better off tapping them into place with a socket/ball peen or using your washer/bolt method. Only drawback I can see to washer/bolt is that it will give case a chance to cool down and bearing a chance to warm up.

Thanks for the input.
 
Only drawback I can see to washer/bolt is that it will give case a chance to cool down and bearing a chance to warm up.
No need to heat the case or cool the bearings. Simply draw the bearing into the case by tightening the nut while securing the head of the bolt by whatever means happens to be convenient for a particular case half. Very simple and effective method I wish I would have stumbled across years ago.
 
Saw is partially disassembled; just gotta split the case and tap the old bearings out. That'll happen today or tomorrow.

In the meantime, what do y'all think about these air filters? Looks like three different styles. The mesh one I had in my parts stash. The used flocked one came off a saw, and the new flocked one came from eBay. Looks like the new flocked one has some n*pples on the bottom over the carb to keep it from collapsing.

Any thoughts on which style is best/preferred?

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Many prefer the metal screened filters for exceptional air flow and easy cleaning with solvent or gasoline. but the newer style in the middle is generally thought to provide the best filtration. The early flocked screen type is obviously prone to deterioration and the least desirable. That said, the frame can be re-fitted with UniFoam
using a little creativity for a decent oil film filter akin to a poor man's MaxFlo setup.

Out of curiosity, how did your bearing replacement go? I'm interested to know if the main bearings were the actual cause of your racket or whether the big end rod bearing may have been the culprit instead..., if not something else altogether. Doesn't seem like a dirty bearing would be loud enough to be noticeable over the saw running.
 
Many prefer the metal screened filters for exceptional air flow and easy cleaning with solvent or gasoline. but the newer style in the middle is generally thought to provide the best filtration. The early flocked screen type is obviously prone to deterioration and the least desirable. That said, the frame can be re-fitted with UniFoam
using a little creativity for a decent oil film filter akin to a poor man's MaxFlo setup.

Out of curiosity, how did your bearing replacement go? I'm interested to know if the main bearings were the actual cause of your racket or whether the big end rod bearing may have been the culprit instead..., if not something else altogether. Doesn't seem like a dirty bearing would be loud enough to be noticeable over the saw running.
Thanks for the filter info.

The bearing replacement was fine. The saw didn't have spark, so I didn't get it started before I tore it down again. The noise was audible when cranking it.

After I installed the SKF bearings, noise went away. Saw has been reassembled, runs great, oils great. Just need to tune it. Had planned to throw it on eBay but there are several 075's listed now, so I may wait a bit.

Scott
 

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