Stripped crankcase cylinder bolt hole

[ernestro]

Hi there!

first post i think. (to skip the story and go straight for the question, scroll down to the bottom)
Been reading here for a while, learned A LOT in the last two years. Had absolutely no clue about fixing chainsaws or anything 2-stroke before, but now i can do some maintence and fixing..
Thanks for all the info so far..the best forum around! Will contribute when i pull myself on a green branch.

So...i got a slightly beat up 365 Special for a good (200$) price 2 years ... got it running pretty good - the fine mesh filter in the carb was completely stuffed with oily wood dust residue. It was idling alright (although i don't know how it managed even that), but in the cut it would bog down completely.
Did a bunch of part replacements (fuel filter, flywheel bearing, sprocket, blade, x-cut chain ... ), so i', a bit invested in it, therefore i don't want to bin it straight away- or maybe at all.. i like the 365 sp... i'll just get another used one and have this one for parts..

It ran well enough for my needs, even though it had only 135PSI compression, as there was some slight scoring seen on the exhaust side, but still - ran enough to work with.
... but then i lent it to my inlaws ...
well... the result was that it wouldn't idle and run unless pushing the throttle....something was apparently wrong but they would keep on cutting
so i tore it apart, and voila...
scored piston, piston skirt chipped off (ok, the skirt might have happened before i bought it, as history was unknown


I decided to try to save the jug... i bought a new meteor piston and removed 99% of aluminum transfer in the jug (no acid) ...
Since the whole saw is a experimental first timer project, i decided to widen & smooth out the lower transfer end...(Not touching the science of port timing yet

I've got nothing to loose... If i messed up the cylinder, i'm most probably upgrading it to a 372 P&C anyway... WIN WIN



SO, finally getting towards the QUESTION.
Everything went fine (but as a first timer extremely slowly and carefully, also i have limited time for this new found hobby)
until i tried torquing down the cylinder.
In the workshop manual, it says 10nm.
Two screws clicked okay, on one i was getting suspicious, but one gave up on the thread.. .
Wrench was set in 10nm for sure...
How do you tighten your cylinders down?
Torque wrench or by feel? Till it's snug + one or two /16 of a turn?

I have 3 Torque wrenches...to work on the family cars...i bought them with the sole intention NOT TO STRIP threads or tear bolts (or o.t.o.h. have something come loose on the highway)
well...that's exactly what i did here...
I stripped the thread in the crankcase....after all that work Still not sure how... tired material? Was someone before me there and overtightened already, so it was ready to get stripped on the next tightening?)

I read about possible solutions... i guess thread lock only is out of the question on such a critical part..
Thought about helicoils and/or timeserts (got no tools&experience yet)... but read somewhere that it might be worth to try
to drill and tap a new M6 thread.

So i do have taps, therefore i went this route. I read i can still put a helicoil/timesert, if the tap fails to work?



THE REAL QUESTION:
Can i get away with tapping just this one stripped hole... or should i do the same for all 4 cylinder bolt holes?
If i try to tighten by feel...will the clamping force be distributed evenly across the mating surface?

I always do tighten bolts in a circular (or other appropriate pattern) manner,
taking great care to increase force very gradually so i don't bend anything...


what's the worst thing that can happen?
I would like to keep the thing.... don't mind too much if i have to swap the P&C
... but would not be happy to destroy the crankcase...


Thanks a lot, for any kind of info!

 

[Dennisthemenace]

If it was 5 mm drill and tap the bad hole at 6mm and use blue loctite. Looks like a real bad air leak or straight fuel. Probably the latter if you lent it out.
Vacuum and pressure test before trying to run.

 

[ernestro]

The scoring coincides mostly with the decompression hole, which i have plugged 2 years ago...
the valve was leaking (bubbles in a jar).

Maybe it was scored like this from the getgo, hence 135PSI compression? It did cut wood well so i didn't bother then.
And now it just happens to, coincidentally with the lending, refuse to run anymore... it did have the fine filter in the carb clogged a bit again...
But the last time,
it would idle but bog in the cut,
now it keeps cutting out at idle, but would run, though struggling, in the cut.
i didn't tear it apart yet then...just looked through the exhaust port and sparkplug hole..
.. anyway..

drilled with 5mm ✔
tapped with 6mm ✔

should i do this with all holes?
I would prefer not to unless absolutely neccesary...

or rather try with 1 hole and report the consequences here :> for the science..

 

[Mad Professor]

I'd run a 5mm tap down the other holes then see how a screw threads in. If they are "screwed" tap out those or install helicoils/timeserts. Pressure/vac test it and rinse out the case with mix. See if you feel any of the missing piston material in the bearings, also check inside the muffler..

There is a lot of carbon above that ring and the ex port looks pretty oily. That didn't help things and maybe that was how the rings got smeared?

 

[Gord404]

II would spend just a little more time on that cylinder and get the rest of that transfer out.- a finger and a little emory or sandpaper cloth works well.

 

[ernestro]

hey there, thanks for the comment - the picture is not up-to-date, it does not reflect the current state of the cylinder- i was just looking for a pic to show the scoring from the decompression chamber as it was...

It did take a lot of time to get the transfer out... it's almost completely gone ...

So...should i torque the bolts down or just make it really snug? .. sure wouldn't want to strip the bolts again with that torque wrench...

 

[SteveSr]

It did take a lot of time to get the transfer out... it's almost completely gone ...

Almost only counts in horseshows and hand grenades! It needs to be COMPLETELY removed to prevent future problems. Any transfer will either smear on a ring or prevent it from seating/sealing.

 

[Dennisthemenace]

U

hey there, thanks for the comment - the picture is not up-to-date, it does not reflect the current state of the cylinder- i was just looking for a pic to show the scoring from the decompression chamber as it was...

It did take a lot of time to get the transfer out... it's almost completely gone ...

So...should i torque the bolts down or just make it really snug? .. sure wouldn't want to strip the bolts again with that torque wrench...

There has been trouble previously so I'd torque em. You won't strip the threads with a little 1/4 drive and the correct long allen driver set at 12 or 15 nm, whatever the book says. And use blue loctite

 

[Vintage Engine Repairs]

If it was 5 mm drill and tap the bad hole at 6mm and use blue loctite. Looks like a real bad air leak or straight fuel. Probably the latter if you lent it out.
Vacuum and pressure test before trying to run.

This ^^

 

[stihltech]

Always torque cylinder bolts. If they strip, they needed repair anyway. If they were self tappers use a helicoil and a threaded bolt (screw).

 

[ZeroJunk]

Well, you had the meat to go to 6 mm on the one stripped. I certainly would not screw with the ones that aren't stripped. Never forget, perfect is the enemy of the good.

 

[ernestro]

Almost only counts in horseshows and hand grenades! It needs to be COMPLETELY removed to prevent future problems. Any transfer will either smear on a ring or prevent it from seating/sealing.

Gah...i have left a couple of specs yess...lost the will to rub that thing, completely : ) ... i can't feel the transfer...not even with a sharp toothpick.. but what i've found beneath the transfer... hmm yeah..well... yall please give comment.

I guess the cylinder wall has deeper scratches, plus looks like tiny cracks on the top of the cylinder. i do feel those with a sharp tooth pick.
I hope i don't get it in my face, if that's even possible? ...
Anyway...it's just waiting to eventually get a 372 P&C, so i'll try to run it for the science. A tank or two (if i make it), then check the internals.

doc ... how bad is it??


Uu...shiny..looks perfect...


NO...naa..a-ah..far from it. But let's see if there's still life in this jug..
Inspite of this↓



The damn thing don't look so bad anymore...


Well what do you know...depends on the lights..





Oh..i forgot..i also slipped while turning the circlip.
but have sanded it out pretty good. I hope it's not fatal.

 

[ernestro]

Older pic, but still... is it cracks?

 

[ernestro]

Looks like tiny holes...


Anyway...sorry for the offtopic..

Well, you had the meat to go to 6 mm on the one stripped. I certainly would not screw with the ones that aren't stripped. Never forget, perfect is the enemy of the good.

Thanks! I was hoping i'll get some keep it simple stupid + don't fix it if it ain't broke advice...
"Never forget, perfect is the enemy of the good." Yea please explain that to my "superior" at work

There was plenty of meat though...so combined with↓

Always torque cylinder bolts. If they strip, they needed repair anyway. If they were self tappers use a helicoil and a threaded bolt (screw).

.. i'll tap the ones who fail the test..

U

There has been trouble previously so I'd torque em. You won't strip the threads with a little 1/4 drive and the correct long allen driver set at 12 or 15 nm, whatever the book says. And use blue loctite

The funniest thing is... check this table...maybe i've got wrong data but...


i went around tightening gradually.. first i set the t.w. on min. = 6nm... all bolts clicked...
I said okay... let's go to 8nm (i really didn't want them to strip... i do have a proper long driver with a 1/4 t.w... 6-30nm it's not the shortest...but .. well.. maybe it's out of line, but i never stored it tightened.. .
so 8Nm goes well with 3 bolts, but one starts to feel funny..
maybe i shouldn't have continued, or maybe it's okay to filter out crap fasteners...

What i find interesting is that the original M5 bolts are supposed to be at 10Nm by Husky factory workshop..
but they only handle top torque 6.3 Nm ? They are 8.8 grade, i checked.
If the bolts handle that "little", what does that mean for the magnesium hole? It's definately softer than the bolt.


Should a M5 bolt be torqued like a M6 one? Don't know...

To be continued...

 

[pioneerguy600]

The area that looks like cracks is most likely to be where the cylinder plating ends near the top of the cylinder, ring of death to us porters.

 

[pioneerguy600]

Looks like tiny holes...
View attachment 1098403View attachment 1098404

Anyway...sorry for the offtopic..



Thanks! I was hoping i'll get some keep it simple stupid + don't fix it if it ain't broke advice...
"Never forget, perfect is the enemy of the good." Yea please explain that to my "superior" at work

There was plenty of meat though...so combined with↓



.. i'll tap the ones who fail the test..






The funniest thing is... check this table...maybe i've got wrong data but...
View attachment 1098406

i went around tightening gradually.. first i set the t.w. on min. = 6nm... all bolts clicked...
I said okay... let's go to 8nm (i really didn't want them to strip... i do have a proper long driver with a 1/4 t.w... 6-30nm it's not the shortest...but .. well.. maybe it's out of line, but i never stored it tightened.. .
so 8Nm goes well with 3 bolts, but one starts to feel funny..
maybe i shouldn't have continued, or maybe it's okay to filter out crap fasteners...

What i find interesting is that the original M5 bolts are supposed to be at 10Nm by Husky factory workshop..
but they only handle top torque 6.3 Nm ? They are 8.8 grade, i checked.
If the bolts handle that "little", what does that mean for the magnesium hole? It's definately softer than the bolt.


Should a M5 bolt be torqued like a M6 one? Don't know...

To be continued...

Torque both 6 and m5 the same, not a large enough diameter to make any difference in clamping force.

 

[ernestro]

The area that looks like cracks is most likely to be where the cylinder plating ends near the top of the cylinder, ring of death to us porters.

... does not sound too good. What is it about? Area of greatest material stress?

 

[SteveSr]

Older pic, but still... is it cracks?

Any issues above the ports could have an impact on the compression.

From the vertical scratches it looks like this engine suffered from dirt ingestion due to an air filter/leak issue. You need to fix this if it hasn't been already.

 

[pioneerguy600]

... does not sound too good. What is it about? Area of greatest material stress?

As long as the piston rings do not travel over the edge of the plating then most all saws have no problem with the plating ending before it contacts the cylinder head, the ring of death I mentioned only comes into play as a problem is if the cylinder base is machined down, thus dropping the cylinder head and the rings can contact or run up over the top edge destroying the rings and piston. As long as the cylinder is left stock then the plating ending a bit below the cylinder head is no problem.

 

[ernestro]

I might do the gasket delete on the next round,...i guess there is probably enough room for that..will measure squish after assembly...
but will probably not be machining the base down anytime soon..


Yeah the abrasive for the vertical scratches probably came the really dirty fuel filter & carb interior (thick layer inside)...airfilter was acceptable, but the saw has not been cleaned for a while i would figure...


Maybe some dust came through the leaking decomp valve...which is a bonus for the already knocked off a/f ratio, plus starving fuel from the clogged carb...
real lean mean machine..