Shock! Horror! sheared flywheel bolts!

[Nambo]

Whilst I admit the prospect of fitting the engine/Gearbox complete seemed a bit daunting, I was swayed by considering my clutch plate was probably rusted solid to the flywheel after 4 1/2 years.

So took the gearbox off today, unbolted the pressure plate and the clutch plate just fell off with gravity, no rust at all!
"That was a complete waste of time" I mused, but then, purely out of the goodness of my heart, I put a socket on the now revealed 4 flywheel bolts to make sure they where as tight as they looked.
The first one just turned with no pressure and fell out, discolouration revealed it had been completely sheared for a long time, heaven knows what was holding it in.
The next one sheared with a slight pressure on the spanner, fresh metal revealed that had been only sheared by 75%, the other two were fine.

Now, is this a problem on the Stag, maybe the reason the MK2 used 6 bolts?, (I dont know why my MK2 has a four bolt crank?, or does Rimmers get these made in China for I fitted new ones around 95.

I torqued these by the book, though locktite would have meant the threads were not "clean, dry threads", should I have torqued them less?

Now can anybody recommend a supplier who is going to provide strong bolts please?, these were quite easy to drill through, I drilled 4.5 mm holes fairly central and a gnats whisker short of breaking through, Whats the best stud extractor these days?, do you think 4.5 is big enough? those bolts do have loctite on, some special blue stuff.

Iam buggered if they dont come out.
I suppose the crank is too hard for a mortal to drill through to tap for the extra two holes?, my fly wheel had the six.

So what could make them shear in use, they certainly torqued up ok, is it when things get hot and expand its too much for them?

Worried Pete

[jpyke]

Hmm that's an interesting one, I thought the 4 bolt cranks were only used on the early prototype 2.5 V8s and that they went to 6 bolt when they increased the capacity to 3L. I could well be wrong on this though... I'm sure someone will be along to correct me.

I doubt you'll drill the crankshaft, not if its been properly hardened. I've not had much joy with extractors in the past but if you manage to get the bolts out, Peter at LD Parts should be able to supply decent replacements.

James

[Stagnant]

Hi Pete. I'm really no Stag guru or expert so can't help you except to say that I read that the early Mk 1 had 4 bolts and this was soon changed to 6 because the strain was too much for only 4. I wish you all the best of luck - and I'm sure some good advice is on its way!
Mark

[StagnJag]

According to the parts book, the crank changed from 4 to 6 bolts at engine number LF273E so it changed very early.

Unfortunately, the parts book doesn't specify the size of the bolt, it has a specific part number (151018) which would suggest that it is non standard - I guess high strength. Rimmer Bros show tham under part number UKC3044, but don't give nay clues about size or strength.

Rgds

Dave

[flying farmer]

The early Mk1 did have 4 bolts, I once had an engine with a 4 bolt crank.

I must admit I didn't like the look of it at all so I drilled and tapped it for the two extra bolts.

It took quite a bit of effort to break through the surface hardening, but once through it was no problem to drill and tap it.

The reason your mk 2 has a mk 1 crank is simply because it will have been swapped for a reground one at some point in the past (probably several times knowing the average Stag engine)

Neil

[Rubce]

Hi Pete

If the threads are not dry i.e have loctite or copperslip on them then you need to be reducing the ROM torque valves by about 20%

Hope you get it all sorted.

Regards

Bruce

[milothedog]

Hi Pete

If the threads are not dry i.e have loctite or copperslip on them then you need to be reducing the ROM torque valves by about 20%

Hope you get it all sorted.

Regards

Bruce

Don't use Copper slip They should be fitted using a sealant to prevent oil coming up the thread (there is a Main Bearing directly behind it) and leaking in to the Bell Housing. The originals came already treated ready to fit.

Ian


Hope you have deep pockets http://www.ldparts.co.uk/shop/shop.p...1b078a92963813

[Nambo]

Don't use Copper slip They should be fitted using a sealant to prevent oil coming up the thread (there is a Main Bearing directly behind it) and leaking in to the Bell Housing. The originals came already treated ready to fit.

Ian


Hope you have deep pockets http://www.ldparts.co.uk/shop/shop.p...1b078a92963813

I wouldn't begrudge paying nearly £10 for each bolt if it was something special that was required to do the job, but they are the same as the ones I bought with the blue sealant on and plainly they failed, why should I pay so much for something that doesnt seem as good as an ordinary 3/8 UNF quality bolt and thick washer of which I have plenty of just lying around.

Any reason I have to use the listed bolts, can I just use good quality British bolts and washers and use a good gasket sealer like "Yamabond" that cost me 50 quid for a tube and glues things in place as good as it seals?

[KOY 23]

I think its down to "peace of mind" P Howells sells good stuff and I respect his choice. I would not want the pain of having to split the engine /gearbox again to have to replace them again. Never heard of these bolts shearing before, were they the correct spec, had they been overtorqued before? we don't know. I don't have a tube of your Rambobond which costs more than a set of new bolts.

[StagnJag]

I presume that the 'proper' bolts are supposed to be a higher strength than standard off the shelf bolts. As said above, Peter at LD parts won't stock anything that is under par so his bolts should be pretty good, although in the vast majority of cases they will have been used in the 6 bolt configuration.

[jbuckl]

Triumph wouldnt have gone for 6 instead of 4 unless they had to.

6 would be the best thing for peace of mind.

The ld parts are probably the best researched parts available.

Just my 2p

[mike@thenook]

I wouldn't begrudge paying nearly £10 for each bolt if it was something special that was required to do the job, but they are the same as the ones I bought with the blue sealant on and plainly they failed, why should I pay so much for something that doesnt seem as good as an ordinary 3/8 UNF quality bolt and thick washer of which I have plenty of just lying around.

Any reason I have to use the listed bolts, can I just use good quality British bolts and washers and use a good gasket sealer like "Yamabond" that cost me 50 quid for a tube and glues things in place as good as it seals?

I used these proper bolts from LD when I re-built this time, they have a special insert in the thread which seals when they are tightened up to prevent leaking and loosening, its probably something like loctite but I'd not be happy using 40 year old bolts again in such a critical area. The WSM says they must always be replaced and not re-used.

Cheers,

[Matt]

On my Lotus twin cam (6 bolts) the 'standard' flywheel bolts (as opposed to super trick ones) are only £20ish for a set of six via Burton, but that is for standard Ford bolts so a bit more common than the Stag. They do need to be torqued up to 45 ld/ft so must be hi tensile bolts - 3/8 unf according to the ROM. The sealing I would have thought should be OK with Yamabond I would have thought, or Loctite stud lock and seal or some such.

[Nambo]

I doubt you'll drill the crankshaft, not if its been properly hardened. I've not had much joy with extractors in the past but if you manage to get the bolts out, Peter at LD Parts should be able to supply decent replacements.

James

So today, I thought I would at least try and mark the position of the two extra holes using the flywheel as a pattern so the engineers will know where to drill as by then, the flywheel will be back in the car on the new crank.

I firstly machined down a couple of small lengths of alloy tube so they would be a tight fit in the flywheel holes and act as guides for a 6 mm drill that fitted down the center.

Now the drill was cobalt, but it was so easy to drill the marks in the crank end that I was encouraged to press on.
With no difficulty at all, and just a hand electric drill, I went through the case hardening and then frighteningly easy through the interior metal of the crank itself, the thickness of the swarf indicate the drill went through like butter, a bit harder getting though the case hardening at the back.

I then used my "Q" sized drill I had bought on American e-Bay as the correct size for tapping 3/8 UNF, firstly by drilling the centre holes in my alloy guides, then through the crank itself which I then successfully tapped.

I also now drilled out one of the broken bolts without harming its thread.
The only thing I couldnt do was the other broken bolt that now has the broken tap in it, so its still down the engineers after all, lets hope they can do it!
(The eazy outs were indeed useless so in my desperation to try and get the bolts out without stripping the engine, I had tried a left hand thread tap, 4.2 mm being the largest size I could find, It gripped as planed, but wasnt strong enough!).

[martin]

Nicely done, I've always regarded Easyouts as a fake, the buggers ALWAYS break, I haven't dared use one for decades, there used to be a twisted square section easy out that worked quite well, but I've not seen them for a long time. If a drilled broken stud/bolt won't come out fairly easily, then drilling-tapping or spark erosion are really the only options. Martin.