M5 alu head thread repair options?

[premmington]

How about 1/4" BSW for that bit chunkier thread in the ali?

That would test my tap/drill/bolt collection out too much.

But I can see your thought process...

 

[JOEPRO]

But I'm also in the just swap to M6 camp.

Not so simple! In these later con saws the head bolts pass up through the saw body through narrow square holes within a plastic housing. About 5 inches deep. The bolt cap heads don't fit in m6 size.

Then an M6 thread would also require drilling out the aluminium engine housing to allow them to pass through same.

To me, in this instance that will cause permanent damage to the engine casings and if the heli coils don't work then I will buy a new aftermarket barrel which for the fuel injected saws is around £65.

 

[bricol]

Not so simple! In these later con saws the head bolts pass up through the saw body through narrow square holes within a plastic housing. About 5 inches deep. The bolt cap heads don't fit in m6 size.

Then an M6 thread would also require drilling out the aluminium engine housing to allow them to pass through same.

To me, in this instance that will cause permanent damage to the engine casings and if the heli coils don't work then I will buy a new aftermarket barrel which for the fuel injected saws is around £65.

Then sounds like the inserts are the easiest way.

 

[rtcosic]

How about 1/4" BSW for that bit chunkier thread in the ali?

Heathen! So you're the one who does things like that and cause problems for the next poor bloke 30 years later!

 

[MetalMonkey]

I've used EZ-lok inserts to repair manifold threads with good success, not keen on helicoils, I've encountered a lot that have just unscrewed when dismantled, or worked loose over time. Possibly not installed correctly, but the nice thing is you can drill up a size and still fit the ez lok style.

 

[Onoff]

Heathen! So you're the one who does things like that and cause problems for the next poor bloke 30 years later!

College lecturer suggested I use 1/4" BSW instead of M6 to secure my crossbow prod in a bit of dural, 40 years ago.

 

[tigdlo]

Helicoils are only a problem when poorly fitted, apart from the most common not drilled and tapped square, not fitting the insert deep enough can cause problems, for an M5 head bolt in aluminium I would probably want 2 full threads showing above the intsert, especially important for something that will need to be removed and refitted in the future.

 

[Chippie]

Replace the bolts with studs, then you’re not ( occasionally?) having to remove the bolts from the alloy…

 

[Morrisman]

Replace the bolts with studs, then you’re not ( occasionally?) having to remove the bolts from the alloy…

I was just about to post that, helicoils, then Loctite studs in with permanent stuff.
Or epoxy studs in. Tap the hole as deep as it will go with a plug tap first.

 

[premmington]

I've used EZ-lok inserts to repair manifold threads with good success, not keen on helicoils, I've encountered a lot that have just unscrewed when dismantled, or worked loose over time. Possibly not installed correctly, but the nice thing is you can drill up a size and still fit the ez lok style.

I struggle with helicoils - I if I can go down the timesert route - kits are dear - but they a good product

 

[premmington]

Replace the bolts with studs, then you’re not ( occasionally?) having to remove the bolts from the alloy…

That gonna involve turning a set of four sleeve's up - to go thru the top - over the stud and put nuts where there is enough room - possible but not an easy/elegant solution.

 

[Morrisman]

That gonna involve turning a set of four sleeve's up - to go thru the top - over the stud and put nuts where there is enough room - possible but not an easy/elegant solution.

Looking at the size of the current bolts heads I’d think you could get nuts to sit where they do, with a slim socket to tighten them. Its worth comparing diameters.

 

[JOEPRO]

Helicoils are only a problem when poorly fitted, apart from the most common not drilled and tapped square, not fitting the insert deep enough can cause problems, for an M5 head bolt in aluminium I would probably want 2 full threads showing above the intsert, especially important for something that will need to be removed and refitted in the future.

Do you mean to drive the heli coil far enough in so as there is a gap and threads exposed on the lower mating face? So that when the bolt is tightened and pulls on the heli coil it does not start to disengage it at the bottom end?

Some of the heli coil will likely poke up out of the housng presume that wont be an issue in itself.

Replace the bolts with studs, then you’re not ( occasionally?) having to remove the bolts from the alloy…

I'll post more photos this evening or tomorrow to show the saw setup. Studs are not possible on the saw due to the long plastic housing holes the bolts go through before going into the aluminium housing. Aka no room for a nut or socket within the fuel tank plastic housing.

 

[bricol]

If you follow the instructions, drill the correct sized hole, perpendicular to the surface, tap it correctly, install the insert using the correct tool to the depth they suggest (usually 1/4 - 1/2 a turn below the surface), snap the tang off and remove it, then it will work.

 

[JOEPRO]

Ok finally got back to this-

Gasket kit, v coil repair kit & very low range torque wrench.



Old threads:



Set up perfectly true to drill bit with engineers set square:



New threads cut:



All cleaned and blew out. Then red threadlock applied and set the repair inerts 2x threads into the tapped oles.



Really nice fit. The V coil repair kit is very good quality. Huge improvement to the generic no brand kits I was using before so I'll be using this brand from now on. Final step was to use a cotton bud to remove excess threadlock from inside the new coils and a full clean to ensure all swarf is thoroughly removed.

I will reassemble the engine later with more permanent thread lock and allow to cure overnight before use tomorrow.

This is a photo showing why adding M5 nuts was not feasible:

 

[Old Dog]

I'm a little confused as to why thread lock is being used?

 

[JOEPRO]

I'm a little confused as to why thread lock is being used?

To keep the thread insert in place as best as possible for future bolt removal should it be required.

Also - the head bolts have threadlock applied when the saws were originally factory assembled.

 

[Pete.]

You don't usually need threadlock, though I have used it in the past when securing a loose stud into a wire coil repair. Just make sure after it's cured you remove every trace of liquid threadlock from the coil or you'll threadlock the bolt into the coil when you install it. That stuff doesn't cure until it's out of contact with air.

 

[JOEPRO]

I don't think it's critical either way re threadlocker. In my mind it can only help to keep the repair coil in the correct place both when tightening and undoing the bolt in future.

I will be using more threadlock for the head bolts as I said that's how Stihl assemble them. And really the head bolts will be in there for the life of the cylinder. If anything goes wrong the whole cylinder will be scrap anyway.

 

[bricol]

Never fitted them with threadlock. Never had one unwind, including the one in a machine in a plant in Spain that I didn't know had one in - screw felt stiff, so was running a tap in to clear it when I realised . . . Smallest ones I've used are M3.

I wouldn't be assembling anything with permanent threadlock - if I had to, I'd use medium/blue - but not into an insert.