Stihl 075 - Cylinder Shim (not the gasket) - Does it belong?

[Wilhelm]

This is why I refuse to work on equipment other than my own!

 

[drf256]

A Hack job is always fun. Once someone demonstrates they have the ability to do shít work and not care, the issues on their work will just start piling up.

Had that issue fixing problems for people back in the post-JMS era. The “one or two” problems with the saws just kept piling up. One guy here got one that needed 10-20 timeserts alone.

If the builder needed to go from M5 to M6, why would a Helicoil even be needed? Pretty simple to drill and tap for the larger size.

 

[hacskaroly]

If the builder needed to go from M5 to M6, why would a Helicoil even be needed?

As they are the posts are not very straight, I am guessing that they were not drilled out with a drill press. They probably messed up and needed to add a Helicoil. It possible that the donor 050/051 case was jacked up to begin with and this was the best they could do to get it serviceable.

 

[Al Smith]

If you end up with a head knocker some sort of shim or a thicker gasket is almost your only option .However one old Stihl IPL I looked at had several options of gasket thickness but I forgot which one .I'm only assuming that was because of lower octane ratings of gasoline for the intended market location .You know Stihl sold those saws all over the world .

 

[lehman live edge slab]

So true, I was getting ready to start putting the saw together and found that the new clutch side oil seal was too big. The one that came with the new kit was 25x47x7mm and the one came out was 30x42x7mm. The 075/076 IPL calls for the 25x47x7...I did more digging and searching and had about 100 internet tabs open before I found my answer, the previous mechanic (or whatever you want to call the person who worked on this saw) appears to have modified a 050/051 crank case. I measured the piston at 58mm so it is a 075 piston/cylinder, but the crank case needs the 30x42x7mm oil seal which I found in the 050/051 IPL which this IPL lists both size oil seals (I guess depending on the year the unit was built). It appears that all four cylinder studs are in helicoils, which makes sense if they had to enlarge the 5mm holes to accept the 6mm cylinder studs. Also this case is missing the manual oiler which seems to be found on the 075/076s. If anyone has access to a serial number lookup, the SN on this saw is 8580821. I tried looking for a part number on the crankcase, but I am guessing it is on the inside and I don't feel like splitting the case just to see.

Time to order a 9629 003 3400 30x42x7mm oil seal so I can get this thing back together....

Did this saw have an orange cover stating it was an 075? If the cylinder kit was aftermarket the may have given an 050/051 a big bore kit. I have the 050/051 repair manual and I do believe it calls out the serial number the cases were modified at.

 

[Ketchup]

I’ve seen helicoils fail in magnesium and that one will be missing 3 threads. Somebody botched this. Don’t leave that in there. Fix it right or pay the price.

 

[hacskaroly]

If you end up with a head knocker some sort of shim or a thicker gasket is almost your only option

I put the cylinder/piston back on with just the gasket and have it a spin and there was no knocking, the piston moved freely without issue. I think the shim was for the helicoil that was sticking up.

Did this saw have an orange cover stating it was an 075

Yes the air cover has the 075 plate on it.

I’ve seen helicoils fail in magnesium and that one will be missing 3 threads

I tried tightening up the post and it still wiggles like a loose tooth, I will need to get a new helicoil and replace it for sure!

 

[Ketchup]

I put the cylinder/piston back on with just the gasket and have it a spin and there was no knocking, the piston moved freely without issue. I think the shim was for the helicoil that was sticking up.



Yes the air cover has the 075 plate on it.



I tried tightening up the post and it still wiggles like a loose tooth, I will need to get a new helicoil and replace it for sure!

They probably didn’t tap it deep enough. IIRC helicoil kits come with a blind tap but if it doesn’t you probably need it. Considering the top end, I’m guessing that’s a chinese helicoil. Sometimes they come in a kit with a standard tapered tap.

 

[Woodwackr]

They probably didn’t tap it deep enough. IIRC helicoil kits come with a blind tap but if it doesn’t you probably need it. Considering the top end, I’m guessing that’s a chinese helicoil. Sometimes they come in a kit with a standard tapered tap.

They need a flat-bottom tap for a good seat. Otherwise the tapped hole will be tapered and not allow the bolt/screw to go in all the way.

 

[Al Smith]

You would get a better job with a "time sert " .I looked up the Stihl part number on the 075-076 and they are M6 .I think the hole size for an M6 insert is a D sized drill bit .The way they are made uses basically a form tap which expands the deep threads in the insert so it cannot back out once installed .Google it if you like .

 

[Ketchup]

They need a flat-bottom tap for a good seat. Otherwise the tapped hole will be tapered and not allow the bolt/screw to go in all the way.

That’s exactly what I mean by a blind tap. Some saws have pass through bolt holes where you can run a tapered tap really deep but I don’t think 075 is one of them.

 

[hacskaroly]

When I had the post out, the hole does go all the way through (does not bottom out) as seen with the screwdriver passing through it.


I was puzzled as to why the Helicoil was not put deeper. Possibly like other things they Jimmy-rigged it with what they had on hand.


Not much left of the Helicoil. I will look at blind taps and Time-serts, I have neither, but sounds like its time for me to have some on hand!

Edit: I guess I can use a through-hole tap here? Still learning about these.

 

[Ketchup]

When I had the post out, the hole does go all the way through (does not bottom out) as seen with the screwdriver passing through it.

View attachment 425624
I was puzzled as to why the Helicoil was not put deeper. Possibly like other things they Jimmy-rigged it with what they had on hand.

View attachment 425626
Not much left of the Helicoil. I will look at blind taps and Time-serts, I have neither, but sounds like its time for me to have some on hand!

Edit: I guess I can use a through-hole tap here? Still learning about these.

You could probably use either but the square end tap is the one you will want in the future.

A TimeSert or other barrel style insert will use a larger hole and tap than a Helicoil. They also cost more. They are handy for badly wallowed holes or failed helicoils but they are often a “last chance” repair.

 

[Al Smith]

Square bootom is a bootoming tap .

 

[Woodwackr]

Square bootom is a bootoming tap .View attachment 425689

I just grind off the end of an extra tap for this. Start the hole with standard and finish with flat.

 

[Al Smith]

There are many styles of taps for many applications .In this example a two fluke would work better tapping aluminum alloy metal .I've got hundreds from #2-56 up to a 2" tapered pipe tap ..The big pipe tap takes a large wrench with a cheater bar .I've only used it for chasing rusty threads on tractor exhaust manifolds .

 

[Al Smith]

Now then thread failure .In steel the depth of the threads can be the same as the rod diameter IE: 6 mm .Cast iron is 2 times and aluminum is 4 times .With an insert,not a helicoil the thread diameter is larger than the fastener providing a more solid anchor base . I think in this saw it was a design flaw too shallow because for max holding power it would need to be 24 MM or nearly one inch deep .
Little known fact .Roush Racing that builds Ford racing engines (Nascar ) use time serts on every criticle fastener on those engines .As well Ford as a company use them for repairs on new engines .Doesn't happen that often but does happen ,Like the final reaming of the tap hole is over sized because of a faulty carbide reamer . Something like that they catch it rather quickly due to the testing done automatically in the building process .Part of my job was calibrating those machines .