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MG MGA - Thermometer housing studs
|I tried to replace the studs today. I spent time searching the site and came up with a spec torque of up to 15 ft lbs.|
I tightened it down and the threads on the nut end completely stripped.
I'm grateful I didn't break a stud,but I'm at a loss.
Bad torque wrench?
Bad batch of studs?
|15 ft/lbs sounds about right. What torque did you need to get the damaged stud out? Where they new studs? Was it a 1/2" or 3/8" drive torque wrench - lower limit of 1/2" drive|
|The damaged studs came right out without much torque. Studs were brand new. 3/8" drive torque wrench.|
One note, I used Permatex on the end of the stud in the block as noted by Barney. Not sure if that impacts the bolt end of the stud.
|You say they are new studs. Firstly we assume they are the correct stud (not made from mild steel) and the threads are correct as they fitted the head. |
If the nuts are also new, have you checked they are the correct unified thread and feel a good slack-free fit on the studs?
15 ft lb torque would be fine on this size of thread. If the torque was too high I would expect the stud to pull out and strip the thread in the head first!
Await the outcome...
|Studs and nuts were brand new from Moss.|
I am starting to wonder about the torque wrench. It is quite old
|Depending on the type of wrench did you leave it under tension over the years or back it off? Common mistake. Any good machine shop will have a tester. Worth checking.|
From my military days the guys in the hangar tested the torque wrenches every day.
most torque-wrenches are notoriously inaccurate at the low end of their ranges and for the reasons you have discovered, you need to be wary of using them below about 25 Ft Lbs.
I would probably just firmly hand tighten the thermostat housing nuts, the gasket is quite squashy and doesn't need much pressure to seal it.
If you get any seep-age you just need to nip it up a little more.
If you would rather torque it to the correct figures then you will have to buy a "low-range" torque wrench.
They are designed for motor cycles etc and are very accurate.
This is a link to one.
|This list of torque wrench settings is for the 18G/18GA engines but I use this since these engines are very similar. This list refers to "Water outlet elbow nuts" which I assume are the nuts that hold the thermostat housing on and it says 8 lb. ft.|
I have an inch/pound torque wrench that I use for the low torque nuts.
|Am I the only one who has never bothered to use a torque wrench on this item? Snug is good enough. All you need to do is hold a few PSI of water in and there is no chance of warping the cover or anything. You would break the studs long before that happened. In half a million miles of driving M.G.s, I've never had a leak at this location. Just use a quality gasket, no sealer required, and snug them up. I like the Moss premium gaskets. I also like to put something on the block side threads to prevent corrosion. Anti-seize works well in blind holes, and Permatex on through holes.
As for stripping out the nut, sounds like a bad nut to me. I can't imagine a torque wrench being so far out as to exceed the strength of the hardware. The nuts are nothing special, so you can just go to the hardware store and get another one for a few cents.
I am with you. I rarely torque any of the nuts and bolts. The only engine ones I recall ever doing are the main bearings, conrods and cylinder head. The rest very much as you say.
|I have alway done as Steve.|
|I'm with the 2 Steves and Paul in that I only ever hand tighten the studs on the thermostat housing.
On the subject of thermostats, when I did an engine change a couple of years ago, I decided to replace the thermostat at the same time. (The original thermostat was about 9 years old.)
Before I fitted the new one I thought I would just check to see how they compared when dropped into (almost) boiling water.
I found that they both opened very quickly but the new one opened almost twice as far as the old one.
So, even if your thermostat is working, it may not be working as well as it should and it is worth replacing on a regular basis.
|I use a 1/4 drive low torque wrench for all the places that are hard to get to when things are assembled, like the nuts that hold the carb manifold onto the head. I don't torque up hard as it is long enough that it would be easily possible to strip threads if I went in hard. But I see others over tightening things all the time.
There are times when I pull out a old 1/2 in drive torque wrench to get enough leverage on nuts done up by body builders - one car I did a gearbox on took three hours to get the engine out because we had to fight with literally every single nut and bolt, and the impact wrench was struggling on some even with the air pressure turned up to max. Normally I reckon with a comfortable 90 minutes
|Colyn with reference to your comment. most torque-wrenches are notoriously inaccurate at the low end of their ranges and for the reasons you have discovered, you need to be wary of using them below about 25 Ft Lbs. if this is correct how do you know that the one you Recommend is not the same, I must admit I would be very weary of a £29,99p torque wrench, |
Very many years ago I had a similar experience to Tysen when using a standard size 1/2" drive torque wrench to tighten down the thermostat cover and I stripped the threads.
The problem was that the spring inside the wrench was virtually totally loosened off at such a low setting and was not really controlling the torque at all.
Standard size wrenches work better at middle to higher settings as the spring inside is working the click-mechanism more effectively.
Also, I personally would tend to trust the the accuracy of the wrench more in its mid range settings rather than at its highest or lowest settings.
Lower range wrenches are designed to work at low torque levels and so 15 ft-lbs is well within their normal design range.
I wasn't particularly recommending the wrench I sent a link to, I was just trying to give Tysen an idea of what is available.
The other point of the torque wrench is to be able to tighten down a part with equal amounts of torque on each bolt or set-screw head.
|Thank you for your reply Colyn, very interesting|
|I remember calibrating my torque wrench by holding the wrench in a vice then rigging up a long bar welded to a socket that fitted on the wrench. I marked off a number of feet on the bar and hung a known weight at a certain length and noted the reading at which the wrench went click - length in feet x weight = ft lbs.|
|Steve, that's exactly how I periodically check mine for accuracy. I check with two weights in the range I normally use.|
|When I was a student we had torque wrench in the lab that went up to 140 ft/lbs. Being used to tightening cylinder heads we decided to find out what 140 felt like. So we clamped it in a large lab vice. Never did find out what 140 felt like as the vice broke. I guess I still owe Birmingham University for a vice.
There is an MGA connection to this story as the other 2 guys I shared the lab with in 1968/69 both had 1958 MGA Coupes. On graduating they were both selling theirs and I bought the cheap one for £100, my first A.
I was wondering, when you checked your torque wrench, was it reading accurately?
Also, I was curious as to how you could re-calibrate it because I would like to check my own wrench.
I cannot precisely remember, but I think it was fairly close. It is a dial-up torque wrench. I recall setting it up for a specific job, say 40 ft/lb. I hung a 10 lb weight at 4 ft, then used whatever setting made the click.
I wonder how many people leave their dial-up torque wrenches under strain after use? I always slacken mine off.
I would imagine that any respectable machine shop keeps a calibrator. Might be worth the ask next time you are in one. I know from my military days they kept one on the wall outside 'stores' in the hangar.
Next question. How do they calibrate the calibrator?
|It was a torque wrench problem of one type or the other.|
I used an inch/pound wrench and it worked fine.
|Thats good to know Tysen, glad we were all on the right track, thanks for updating us.|
|My primary torque wrench is about 15 years old and every time I've checked it, the accuracy has been almost spot on. Lucky me I guess. I usually check it once every couple years. Granted I'm not able to do it as accurately as a professional, but if it's within a pound at 50 then that's more than close enough for anything on an old car.
It is bad practice to not return the wrench to zero as soon as you are done. Not to past zero, as some types can reportedly be thrown out by stretching the spring the wrong way. Right to zero.
Calibrating isn't difficult and there should be videos online on how to do it on different types. There are also services who can do it for you on an accurate calibrating rig.
This thread was discussed between 28/05/2019 and 02/06/2019
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