Stripped rocker pedestal nut

Side valve, 803, 948, 1098., 1275 and Vizard mods

Stripped rocker pedestal nut

Postby mark wilson » Sun Dec 11, 2016 8:49 pm

I've rebuilt a Midget 1275 engine, with a brand new Mini Mpi head and all new studs and nuts. Started torquing down the head in the normal sequence, got to the final round of tightening and one of the short rocker pillar studs stripped before I got to 25 ft.lb. The UNF upper part, not the UNC thread into the head. Decided to carry on with the sequence and deal with the damaged stud later, but got to the second short rocker stud and the same happened. I've now slackened all nuts off and will have to get two new studs.

Have I done anything wrong? I've used new plain washers, then spring washers, then new nuts. I've tightened the inner rocker studs in sequence with the outers, using 40 ft lb on the head studs and 25 ft lb for the inners. Nuts all threaded on carefully by hand, no crossed threads.

I'm no expert, but I've changed about half a dozen a series heads before without problems.


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Re: Stripped rocker pedestal nut

Postby Panky » Sun Dec 11, 2016 10:17 pm

Where the threads dry? The studs could have been on there way out anyway due to being over-tightened in the past. Might as well get a full set of studs and nuts to be safe.
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Re: Stripped rocker pedestal nut

Postby The vast minority » Mon Dec 12, 2016 5:27 am

Sounds like cheap studs to me.
Or a torque wrench problem
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Re: Stripped rocker pedestal nut

Postby mark wilson » Mon Dec 12, 2016 8:53 am

The studs, nuts and washers were a complete new set from Minispares, not particularly cheap. The torque wrench was calibrated professionally two years ago, but before I bought it second hand. I've not had any reason to doubt it so far, certainly feels about right.

I don't intentionally lube torqued threads, but possibly wasn't careful enough about keeping them clean.
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Re: Stripped rocker pedestal nut

Postby woodywoodchipper » Mon Dec 12, 2016 3:34 pm

Spring washers are your problem,

shouldn't be any, plain flat washers only,on anything that requires torquing

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Re: Stripped rocker pedestal nut

Postby The vast minority » Mon Dec 12, 2016 4:41 pm

woodywoodchipper wrote:Spring washers are your problem,

shouldn't be any, plain flat washers only,on anything that requires torquing

Alan,


Well spotted Alan, I didn't see or didn't read the bit about spring washers. Absolutely agree, using a spring washer is not correct. The surface contact area between nut and washer needs to be full diameter. If you reduce this by fitting a spring washer you massively increase the clamp-load by virtue of reduced friction under the nut.

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Re: Stripped rocker pedestal nut

Postby mark wilson » Mon Dec 12, 2016 6:23 pm

Thanks, I'm sure you are right, especially looking at the chewed up spring washers. However, the reason I fitted them was that pages AA6 & AA7 of the workshop manual clearly show them (unless I've misunderstood). The manual is for the Morris, not the MIdget, and those pages are for the Series II, but no change was specified for the 1098. All very strange, but fortunately no serious damage done. Do you think I need to scrap the head gasket, having half torqued it and then slackened off, or just retighten in sequence with the new rocker studs and nuts? (It's a decent copper faced gasket)

Mark

PS Al - just seen your For Sale ad. Good to see you have great taste in caravans as well as cars! (Puck 230L)
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Re: Stripped rocker pedestal nut

Postby philthehill » Mon Dec 12, 2016 8:51 pm

Mark
The spring washers (BMC Pt No: LWN205/2A18) are fitted under the rocker shaft bracket stud nuts on all of the 'A' Series including the 1275cc Midget.
The correct torque setting is 25 lbf ft (with the spring washer fitted) as specified in the various BMC/BL workshop manuals.
Unless your torque wrench has a current compliance certificate I would suggest that the cause of your thread stripping is a inaccurate torque wrench.
You could borrow a torque wrench and compare torque settings or purchase a new torque wrench with a compliance certificate.
If you have only half torqued up the head you should be alright with the head gasket when you torque it up to the correct torque which for a 1275cc Midget is 50 lbf ft provided that the original 3/8" dia high tensile studs (Pt Nos: 51H279 & CAM151) are fitted which can be identified by the following - a pointed top, a dimple in the top, stamped 22 or 'Y' on the top face. All other 3/8" dia studs should be torqued to 42 lbf ft.
The 5/16" dia high tensile steel studs (Pt Nos: 51K865 & chs522) are also identified by a dimple on their top face but are still set to 25 lbf ft.
If lubricant is used on the threads the torque setting has to be reduced as the reduced friction between the male and female threads allows for the stud to be overtightened if using the manufactures specified torque settings.
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Re: Stripped rocker pedestal nut

Postby mark wilson » Mon Dec 12, 2016 10:05 pm

Phil - thanks, and great to see you over here! You have a PM.

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Re: Stripped rocker pedestal nut

Postby The vast minority » Tue Dec 13, 2016 6:11 am

Mark

PS Al - just seen your For Sale ad. Good to see you have great taste in caravans as well as cars! (Puck 230L)

Quality :D

I upgraded mine to a troll just last month, it's still unused and has that new caravan smell. Just waiting for spring now. :D
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Re: Stripped rocker pedestal nut

Postby woodywoodchipper » Tue Dec 13, 2016 3:12 pm

have never used spring washers on anything that requires torquing

basic engineering spring versus torque something has to give(thread)

been building engines for over 40 years, some to race spec, so i know what I'm talking about

but go your own way,

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Re: Stripped rocker pedestal nut

Postby philthehill » Tue Dec 13, 2016 4:04 pm

woodywoodchipper
I do not disagree with you but both BMC and BL fitted the spring washer under the 'A' Series rocker shaft bracket stud nut and both quoted 25 lbf ft torque and there is no getting away from that fact.
As to whether it is considered right or wrong depends upon how you build the 'A' Series engine and how strongly you feel the spring washer is needed or not needed.
For what it is worth any standard or near standard 'A' Series engine I rebuild using standard or near standard parts I will always include the spring washer as per the BMC/BL workshop manual.
Alternatively and for comparison my own full race 1380cc 'A' Plus engine fitted with full roller 1.5 rockers on a Manx Racing 7 port 940 head and secured by ARP studs and ARP multipoint flanged nuts does not have a spring washer under the nut but does have a ARP high tensile steel ground washer instead. Those multipoint nuts are torqued up with lubricated threads to ARP torque specification.
Once an engine build deviates from a standard specification anything goes and it will be horses for courses. In the mean time I will continue to advise that following the BMC/BL workshop manual is the proper way to go about things.
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Re: Stripped rocker pedestal nut

Postby woodywoodchipper » Tue Dec 13, 2016 7:32 pm

as you say, without falling out over it

you do yours

I'll do mine,

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Re: Stripped rocker pedestal nut

Postby mark wilson » Tue Dec 13, 2016 10:23 pm

I've just checked my torque wrench. It's a Norbar, made in 2004 and professionally calibrated on the 25/11/2015, and I bought it from a reputable second hand dealer. Definitely not your average cheap Chinese toy, but in view of the discussion above I've done a makeshift calibration using dumbell weights weighed on a digital kitchen scale and hung from the torque wrench at a carefully measured distance with the head in a vice. Might sound makeshift, but I've been measuring things for a living for the last 45 years! This produced an applied torque of 21.44 ft lb, and the wrench clicked at as close to this as possible to view on the sliding scale.

So I'm ruling out torque wrench error. I'm sure that Phil is correct about the original BMC spec, but I have serious doubts about the quality of the spring washers now supplied. They appear to have deformed and prevented the nut from progressing down the stud thread. I'm therefore going to omit the spring washer, keep the torque to 25 ft lb but apply a little Loctite to stop me losing sleep. Please let me know if any of you don't think this is a good idea.

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Re: Stripped rocker pedestal nut

Postby The vast minority » Wed Dec 14, 2016 6:31 am

How about deleting the thread locking agent and doing without? You don't need it for sure.

If you feel like checking and a retorque after a few drives, that gives you an excuse to have another session in the garage ;)

I'm guessing you are in calibration then. I once had an interview for one of the worlds largest fastener manufacturers in which the technical director , whom looked exactly like Yul Brynner suddenly and dramatically placed both hands on the table, gave me a mad stare and and actually whispered "Define torque".

I still remember my answer 20 years later was "torque is a twisting force applied about a central axis and can be said to cause rotation of an entity" I got the job and to this day I travel the land explaining (amongst other things) the effects of lubrication on torque figures that were calculated for dry assembly. clamp-load increases dramatically for the same torque figure where a lubrication is used. The better the lubrication, the higher the clamp load for the same torque and the higher the chance of failure. A locking agent will lubricate any threaded assembly to which it is applied....

Anyway, enough of this torque :lol:

Additional
Having re-read this whole thread properly I must now confess to not reading your original post properly and I thought we were all talking about the actual head studs. Apologies for this. Given the duty of the application and the fact the originals are designed with the spring washer and the joint designed to be torqued to a given figure to take their presence into account then I refer back to my poor quality components theory which was where I started. This seems to be very likely given the spring washers are disappearing in bits up inside the nuts.
I would certainly remove the lot and get better quality components as you don't want bits in your oil. I can have the bolts tensile tested for you if you want to have some data to supply your supplier. I really dislike any new components, they are never of OEM quality and I'd reuse bolts every time before buying something that cannot be checked for serviceability prior to fitting.
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