Stripped crankcase cylinder bolt hole

[ernestro]

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

Didn't even think of it in terms of clamping force... but i knew something was troubling me..thanks.
So...the aproximate difference between M5 & M6 clamping force (@ same torque&friction coeff.) is about 15-17%.
i could adjust the torque by somewhere around that figure..

 

[ZeroJunk]

Let me throw this out there, any of you ever had a saw fail because the cylinder came loose ?

 

[pioneerguy600]

Let me throw this out there, any of you ever had a saw fail because the cylinder came loose ?

NO!

 

[Chevboy0167]

Zerojunk, I had to go pick up a buddy and his Harley because he was riding to work and 1 cylinder came loose slapping on top of the crankcase! Same guy also rode same bike to work another time holding the carb by hand into the manifold boot/mount to keep her going! LOL

 

[L34]

yes on an 066 redeye.
All 4 bolts loose.
Started running funky so shut her down.

 

[ZeroJunk]

yes on an 066 redeye.
All 4 bolts loose.
Started running funky so shut her down.

I have seen one saw with the cylinder screws loose. I assumed he just ran a bad dull chain until he rattled the thing apart. Doesn't seem to be any point in getting the cylinder bolts tighter than spec is what I was getting at.

 

[cookies]

If it was apart before...It is very easy to re use the wrong length of bolt from your pile on the cylinder as they are typically 1-2 mm longer in length than the other fasteners in order to deeply thread into the case. I would prefer a time cert over rethreading to a 6mm bolt and would time cert all 4 holes...time cert kits can be crazy expensive but their holding strength over bare threaded aluminum is greatly higher. Installing a m6 or smaller sized heli coil is surgeons work! even still still bare aluminum that has been heli coiled has a much higher holding capacity than bare aluminum threads. If I were you knowing that you have limited access to tools I would first tape over the bolt hole insidethe case then tape over the case opening then tap the stripped hole to m6 and attempt reassembly at 76-80 inch pounds of torque on dry clean threads.
I have seen first hand torque wrenches produce a very weak click at their lower end range of torque settings (torque wrench is to large) or even fail to click at all on a few fasteners! I find myself missing the older snap on dial gauge read out style for low torque requiring fasteners...you could actually see the force on the bolt change as gaskets smash, bolts stretch as you are tightening and see if the bolt or threads were failing using the gauge so I could stop and disassemble to inspect before a failure happened.

 

[Mad Professor]

If it was apart before...It is very easy to re use the wrong length of bolt from your pile on the cylinder as they are typically 1-2 mm longer in length than the other fasteners in order to deeply thread into the case. I would prefer a time cert over rethreading to a 6mm bolt and would time cert all 4 holes...time cert kits can be crazy expensive but their holding strength over bare threaded aluminum is greatly higher. Installing a m6 or smaller sized heli coil is surgeons work! even still still bare aluminum that has been heli coiled has a much higher holding capacity than bare aluminum threads. If I were you knowing that you have limited access to tools I would first tape over the bolt hole insidethe case then tape over the case opening then tap the stripped hole to m6 and attempt reassembly at 76-80 inch pounds of torque on dry clean threads.
I have seen first hand torque wrenches produce a very weak click at their lower end range of torque settings (torque wrench is to large) or even fail to click at all on a few fasteners! I find myself missing the older snap on dial gauge read out style for low torque requiring fasteners...you could actually see the force on the bolt change as gaskets smash, bolts stretch as you are tightening and see if the bolt or threads were failing using the gauge so I could stop and disassemble to inspect before a failure happened.

I still have the old style Craftsman torque wrenches that just bends the bar , with a pointer and scale. Big 1/2" and small 3/8 or 1/4? Not precise but nothing goes wrong with them.

I only use them for stuff like bolting on car/truck heads/manifolds. After 50 years my wrist/arm knows when things get tight.....

 

[Dennisthemenace]

Let me throw this out there, any of you ever had a saw fail because the cylinder came loose ?

Not if I've done the tightening. And any saw I get I check those, the muffler, the carb, case where accessible, almost everything really then you know you are right to go.

 

[stihltech]

Not if I've done the tightening. And any saw I get I check those, the muffler, the carb, case where accessible, almost everything really then you know you are right to go.

Yes, used to be quite common. Still see it occasionally. Especially if overheated. Big air leak. But cutter WILL NOT STOP. And then the saw does.

 

[ZeroJunk]

What I see is mufflers rattle off regularly. The screws that hold the intake manifolds on blowers and weedeaters back out. Loose screws have an amazing ability to get from most anywhere to the magnet on the flywheel. Mess up the ignition module and spin the flywheel out of time and all that good stuff.

 

[ernestro]

So i haven't had any time for the saw till today...
....had tapped two diagonal holes to m6 and left two original m5's.
didn't cover the crankcase good enough, even though i used tape and paper towels... a bit of dirt & swarf managed into the crankcase,
so yea...lucky me had to flush that out as well.. .


I was planning to stick with the advice - to not bother with clamping force difference...
but i guess i'm just too curious had to look it up.

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

Found a nice tool to calculate clamping force (yeah lazy), but the equation is simplified, leaving out pitch....
https://www.engineeringtoolbox.com/bolt-torque-load-calculator-d_2065.html

So yeah...maybe i'm complicating things...but 17% (=5÷6) difference is out of my tolerance band either way - it doesn't hurt to even out the force...

I used 20% torque reduction because of Loctite (blue) - read that somewhere. ... . Also read that you can use dry values - either way... i just didn't wanna snap it again..so i went conservative...

Now i'm just left with fixing my vac/pressure pump... holds pressure but not vacuum
and then i can finally p/v test this mean machine...

 

[pioneerguy600]

I have torqued them the same value without ever stripping a cylinder attaching screw,10 - 11 Nm or 7 - 8 ft. lbs for them all I say for my builds, never had one come loose on its own.