Morris Minor Owners Club

Hi there
At sometime in the past with a previous owner a thermostat housing stud obviously snapped approx 1/4 inch below the surface of the block. Someone attempted to drill it but with a slightly oversize drill !
Bearing in mind the torque is relatively low has anyone tried one of the various epoxy compounds to fix a thermostat stud?
If so - did it work??!!

The broken thermostat stud you refer to is located in the head not the block and the stud thread in the head is 5/16" UNC - therefore I would suggest that you discard the idea of a repair using epoxy resin and use a 5/16" UNC helicoil insert.
The helicoil insert requires a slightly oversize hole so as to enable the insert to be fitted.
http://www.ebay.co.uk/itm/5-16-UNC-Heli ... Sw0vBUdcN1

Phil

Thanks Phil
Really helpful. Would s helicoil work if only 1/4" depth hole available ? If not I can attempt to drill out further carefully.
Yes I realise it's the head. Dangers of posting early in the morning when brain still half asleep
Thanks for the link.
Stuart

You need to drill out the hole deep enough to allow the fitment of the helicoil. 1/4" is not sufficient.
The two 5/16" UNC blind holes are 3/4" deep. The third hole is bottomless and open to the coolant.
The 5/16" UNC thread of the stud is 1/2" deep.
Careful drilling should see you right.
When fitting the new stud make sure that you put a smear of copper ease on the UNC threads so as to stop any future problems. A smear of copper ease on the other two studs will not go amiss.
I prefer to user the paper gasket over the cork gasket with a smear of LM grease on both faces.
I have just had to remove three seized and damaged thermostat housing studs from a large bore head so the problems encountered are fresh in my mind.
Phil

Thanks Phil
That's really helpful.
I will look later to see if the broken stud is the bottomless hole. It's the back right as you look at the car from front.. Ie nearside of the car.
The only possible hitch is that the previous "driller" has enlarged the hole periliosly near the actual water housing.. It's just 2 MM from the rim the thermostat sits in. But anything can be fixed - there's always a way!

Stuart

That is the bottomless hole.
If the driller has only gone in 1/4" you still have approx. 1/2" depth to play with.
The driller cannot have enlarged the hole that much because with the head I have just fitted new studs into - the edge of the 5/16" UNC hole is approx. 1.75mm from the edge of the thermostat location recess.
I am certain that you will be alright.
You could always try drilling the stud hole to the tapping size 6.6mm (6.5mm will suffice) and re-tap the hole that last 1/2"
Here is a link to a 5/16" UNC tap on 'e' bay that is more than suitable for your needs.
http://www.ebay.co.uk/itm/5-16-UNC-HSS- ... 1652440210
As you are going into a bottomless hole you do not need a 2nd or bottom tap.
There are cheaper taps out there but those classified as HSS (High Speed Steel) are best and have less chance of breaking.
Phil

Marvellous. Really helpful. Will give it a whirl this week hopefully although wife reminds me that the garden needs doing!

Whilst car not driveable have taken the opportunity to remove the seats and carpet and will wire brush surface rust from the floor pan and treat with Aquasteel then some old fashioned red oxide if I can get some. Have found a firm in Erdington, Birmingham that can apparently make up Trafalgar Blue paint for the floor pan finish.

Seats need major attention as they currently resemble teacups!

Thank again. I'll let you know how I get on.

Stuart.[frame][/frame]

Stuart
Many thanks for the picture.
Before you start could you please tell me the diameter of the hole already part drilled.
Overall I see no problems with drilling out and tapping the hole but it is important to know the size of the hole as it could influence the size of the stud to be used.
Phil

Morning Phil
The oversize hole is 7.4mm
Thanks
Stuart

Stuart
Thanks for the reply.
With the hole being 7.4mm I.D. and the 5/16" UNC stud threads being 7.8mm O.D. you might just get away with drilling the remains of the old stud at 6.9mm (6.5mm) and tapping the hole at 5/16" UNC.
Put a 7.4mm drill down the hole and spin it a few times to get the centre of the old stud and drill then drill at 6.9mm keeping the drill vertical.
In the worst case scenario fit a helicoil - details above.
Phil

Easier just to drill out oversize and either go metric - or 3/8" UNF. - and clear out the thermocover to allow the larger stud. Saves buying a helicoil kit!

I would advise against drilling out and fitting a 3/8" UNF stud or metric equivalent as the taping drill required is 8.5mm for a 3/8" UNF thread - and a 3/8" UNF stud is 9.5mm O.D. minimum.
From the measurements quoted by the O.P. there will be very little (if any) metal left between stud and thermostat seat/recess.
Personally I would drill and tap the existing hole for the 5/16" UNC thread and if that did not work out fit the helicoil insert using the kit in the link above.
Phil

Agreed -and if possible 8mm is the size I would (and have in the past) use - but i suspect the hole has already been butchered out too wide for that. The real repair would be to fit a 3/8 stud - cut off / file flush and then drill and tap into it back to the original 5/16" stud.

Thank you for all the comments which are much appreciated.

Plan is to turn a collar to fit in the thermostat housing as a true guide to make a pilot hole dead centre then enlarge and tap as suggested by Phil. Hopefully the tap will pick up the old thread and clean it out. Lets see!

All this nice weather and Moggie off the road but never mind. Have stripped the interior out and rusting proofing while weather mean I can work outside rather than the garage which is a little cramped and re doing webbing and foam on front seats - or at least the wife is doing the later job!

Thanks again for your various answers

Like the plan, precision is the key to getting that job right!

That's certainly the way to keep a drill on centre when doing such things, either making a plate up to bolt on or using something existing.

I have got head studs out like this, and saved the original threads and got a helicoil in one of my front damper mounts accurately.

Chronos do helicoil kits at a good price. Think I have one to do for the thermostat on my spare engine I am building, but that's the least of the heads problems at the moment. Been exposed to the elements and may be too far gone, plus broken rocker, valve and bent push rod.

No need for a guide - just spin a 7.4mm drill in the hole and you will have your centre.
Phil

I suppose it's a matter of how forgiving the studs are to drilling as the drill can wander off and of course having a decent bench/pillar drill helps.

I had one of these cheap bench drills that couldn't drill a true hole no matter what, awful thing. £60 on a receivers clearance got me a lovely Meddings drill.

Today was the day! Whilst "Molly" was off the road I have stripped out the interior, rustproofed and primed the floor and reupholstered the front seats.
A bush to fit inside the thermostat housing with a pilot drill hole to make a dead centre hole was made and installed. Soon discovered that unfortunately a previous attempt to drill out the broken stud had resulted in a drill breaking off inside the head.
At this stage I envisaged a new cylinder head and a wife asking me where the money was coming from! However a cunning plan which Blackadder would have approved off was plan B.
An hour and a half of careful drilling (and the breakage of a few fine drills in the process!) resulted in a hole being achieved around the the broken drill bit, otherside of the thermostat mounting. Then able to tap out a new thread and 15 minutes later the replacement stud was happily in place. It didn't take much longer to replace pipework, fill with 50% Inorganic Acid Technology antifreeze and a long awaited road test, which was highly successful.

Whilst off the road I also changed the petrol filler tube to petrol tank rubber connection which was perished, understandable after forty nine year! Petrol pump was leaking badly and I overhauled it with a service pack from Morris Minor Centre Birmingham. An independent engineers inspection of the bodywork/chassis confirmed that the car was extremely solid and sound. It was of concern to note that a well known northern Morris Minor Centre had only recently charged the previous owner a fair amount of money to align the front doors but they still did not align. It took me five minutes to adjust the offside door correctly but the nearside door will need shimming. Shim pack ordered today and will be sorted by next weekend.

So... tomorrow we shall be driving Molly to Bidford-upon-Avon for a picnic lunch by the River. She will never be concourse without a lot of extra work and to be honest we are just enjoying her as a beautiful old car that can be driven in the fine weather in place of my state of the art highly complex new Jaguar, as lovely as it is. You can't beat the old classics!![frame][/frame]