Threads gone in Cylinder block

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Post  Alan Grant on Tue 26 Nov 2019, 3:17 pm

Hi,

Anyone else had issues with the M8 studs in the top of the cylinder block for the safeties? I had the safeties on and off a few times to set them to the correct pressure but after the initial setup they have only been off for hydraulic tests. The studs were fitted and have never been removed.

At the first test, one of the M8 studs came out, threads in the cylinder block have been stripped. We managed to get it through the test by using a Whitworth thread that was slightly larger. This held fine until the test this year and the bolt came out. Also a second M8 stud has also come out, again the threads in the cylinder block being the issue.

I've always been careful when tightening these up so that they aren't too tight, so not sure what has caused this.

Is the best course of action to drill and tap M10 and have a stud half M10, half M8? Or a Helicoil thread insert?

Cheers

Alan


Alan Grant

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Post  lynnr on Tue 26 Nov 2019, 5:30 pm

Hi

I would say Helicoil as it sound like you have a particularly soft casting. The helicoil will be stronger than any other method.
On Crystal she has one stud strip so far. I drilled and tapped the hole deeper as it was a "corner" one so had meat to spare.
If it strips out again I will go Helicoil.
lynnr
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Post  LiveSteam on Tue 26 Nov 2019, 7:27 pm

I'd agree with Lynn, I've got at least two Heli's on my safeties on the agri now, I've actually got a couple of dodgy threads on the rear cylinder cover but they are in such horrible location it will need the block off to do them Rolling Eyes

So while they are still holding and not really leaking then they can stay that way for now.

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Post  iain on Wed 27 Nov 2019, 7:21 am

definitely a helicoil will sort this. easy to do and kits aren't that expensive.

iain

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Post  Alan Grant on Wed 27 Nov 2019, 8:39 am

Sounds like hilicoils are the way to go, will get some ordered up!

Cheers.

Alan Grant

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Post  BurrellSimplicity on Wed 27 Nov 2019, 9:23 am

sounds like the nuts are being tightened too much pulling the thread out the cylinder.. my engine is 20 years old and the safety valves are off each year.. not stripped a thread yet and they are 1/4 BSF so finer than M8! Cast iron is soft and with small threads care needs to be taken. these don't need to be done up so tight. put all nuts on nipped and do opposite corners and sides to spread the load. then just a little nip extra.

The studs should be a good fit in the hole, if they wobble then replace the studs.  I tend to make my own if this is the case with the split die set open to make a larger thread. this then should be a good fit in the hole, use 2 nuts locked together to get the stud in and make sure it bottoms on the end of the hole to lock the thread. the tap will naturally make a smaller thread at the bottom and helps to lock the stud in. file off the bottom of the stud once made so it's a sharp 90 deg instead of a taper, this also helps to lock the stud at the bottom.

you might find that when in steam the nuts are loose due to the expansion of the stud, a tiny nip is all that's needed. use a good gasket and you wont get any leaks!

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Post  LiveSteam on Wed 27 Nov 2019, 7:21 pm

BurrellSimplicity wrote:sounds like the nuts are being tightened too much pulling the thread out the cylinder.. my engine is 20 years old and the safety valves are off each year.. not stripped a thread yet and they are 1/4 BSF so finer than M8! Cast iron is soft and with small threads care needs to be taken. these don't need to be done up so tight. put all nuts on nipped and do opposite corners and sides to spread the load. then just a little nip extra.

Totally agree, that and decent surfaces and good gaskets, I shudder when I see folks winding down small nuts and bolts on stuff as if they are doing up wheel nuts on their car  Shocked  most really just need nipping up and then a further tweek once in steam, I have a socket set that has a screw driver type handle that the sockets fit on and most of the time thats all I do with mine, rarely do I actually find I need to pop the small ratchet on the end of it.

BurrellSimplicity wrote:
The studs should be a good fit in the hole, if they wobble then replace the studs.  I tend to make my own if this is the case with the split die set open to make a larger thread. this then should be a good fit in the hole.........

Now I like that tip  Cool , thanks for the share, that might save the couple of iffy ones on the cylinder covers as they havent actually pulled yet but you can just feel they aren't right and I'd like them a bit tighter than the almost finger tight they are currently.

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