36 replies to this topic

[babsbrown]

Evening everyone,

I'm in the process of replacing the clutch I just hand screwed the flywheel bolt back in the end of the crank to make sure It screwed in ok. However it seems very stiff. The first few threads seem ok and screw in fine, but once it gets half way in I hit resistance. Are they normally like this? I used a proper puller with the cap in place to protect the threads. hopefully if the worst comes to the worst I will rent the perculiar thread Tap and chase it out. Any help is much appreciated,

Cheers Luke

[nicklouse]

If the threads are correctly formed and not damaged there should be next to no resistance.

[babsbrown]

Ah crap! Must be definitely damaged then some how! I might try a new bolt see if that is any better

[Spider]

Check the Threads on the Bolt, but basically, if you can wind it in by hand, it'll be OK. As they are a High Tensile Bolt, the threads don't damage that easily.

Be VERY careful - VERY - if you are going to put a tap in the Crank, it's VERY easy to damage them, ideally you should use a thread chaser for just cleaning up threads.

If you have an old Flywheel Bolt, grind a slot in one side, doesn't need to be much, then check the ends of the thread where you've jut cut that slot, maybe run them through a wire wheel, then you have a good tool for cleaning the threads.

[babsbrown]

Check the Threads on the Bolt, but basically, if you can wind it in by hand, it'll be OK. As they are a High Tensile Bolt, the threads don't damage that easily.

Be VERY careful - VERY - if you are going to put a tap in the Crank, it's VERY easy to damage them, ideally you should use a thread chaser for just cleaning up threads.

If you have an old Flywheel Bolt, grind a slot in one side, doesn't need to be much, then check the ends of the thread where you've jut cut that slot, maybe run them through a wire wheel, then you have a good tool for cleaning the threads.

 

 

 

 

 

 

Thanks for your advice, it’s really throwing me off because I can screw the bolt in fairly easy until I meet resistance, at that point it would move with a socket but don’t want to in case I strip the thread. I will definitely try your tip and see if that helps. If that fails I’m going to find the appropriate tap and see if I can retap the thread . If not I’m tempted to drill and tap it to 3/4 UNF I’ve seen some previous threads in which you have done the same In the past. Did you use a high tensile bolt with a similar sized head? What did you do about the lock tab and washers? Cheers, Luke

Edited by babsbrown, 13 December 2020 - 12:47 AM.

[Spider]

I'm sure it'll clean up and we won't need to get too radical with it.

 

With those that I've had that have been damaged beyond repair, yes, I have drilled and tapped them 3/4" UNF and used a Grade 8 Bolt. I did need to thin down the head of it though. I also had to drill the Lock Plate. I don't use Locktabs on anything (other than Ball Joints) these days, I find I get better results with Loctite 243.

[babsbrown]

I had a go with the slit in the bolt today. It just feels like it's cross threading and is jerky when it's going on n. I will order the witworth tap today and see if I can re-tap when that arrives. Where Did you manage to get a bolt with a head big enough 3/4"uNF?

Edited by babsbrown, 13 December 2020 - 10:10 AM.

[whistler]

You can rent the correct tap from John Guess at Guess-works.

[AndrewT]

Have you put the new clutch assembly and all the washers in place or are you just testing the bolt on the bare crank end?

If the latter then is it possible that the bolt is just bottoming out in the thread without all the other bits in the way packing it out? I've no idea if that is possible (i.e. how deep the crank thread goes) but "halfway" might actually be all the way.

Someone with more knowledge than me might be able to confirm this but it's surprising that the thread could have got damaged.

[babsbrown]

Cheers guys, I might actually give the guessworks one a go, at least I know it will be quality metal and no doubt HSS, the only one I can get my hands on are CS. Yes @andrewT I was wondering whether that was the case my self, so looking down the nose of the crank they seems to be enough threads for the whole bolt to thread down. Perhaps not, likewise I'm not really that knowledgeable with regards to cranks etc...

[AndrewT]

In which case screw it in by hand until you meet resistance then measure the gap between the crank nose and the bolt face. Then measure the thickness of the lockwasher and keyway to see if all the slack will be taken up.

Edit: actually there is also some of the clutch assembly to take into account I think. It's one of those things you don't look at very often and don't necessarily absorb the detail when you do.

One of our resident experts will know.

Edited by AndrewT, 13 December 2020 - 11:56 AM.

[weef]

Before you start cutting threads etc you have to decide where the fault is, is it the bolt or the crankshaft thread . In the absense of  thread pitch gauges, thread chasers or thread combs, to decide what is wrong buy a new bolt and see if it fits. The new bolt will obviously be correct and if you still have difficulty in screwing it in then suspect the crankshaft thread to be your problem and move forward from there. 

[bpirie1000]

Is it the bolt thhat came out?


Any visable damage to threads or the end?

[Revd]

If not the original bolt check thread angle as well as pitch: Whitworth 55 degrees included angle, unified 60 degrees

[Ethel]

Possibly our biggest topic was on the crank thread!

 

Have you had the flywheel off before? Has somebody used threadlock maybe - also not impossible it's been chased with a tap of the wrong thread pattern.