toofast2race Posted February 9, 2019 Posted February 9, 2019 Just loaded my old engine that detonated in late 2014 into my car for a friend who is building it into a Gitfire race car. I knew the crank was toast but everything survived well - after seeing the break, I think I know why Triumph stopped bothering to cross drill them!
RogerH Posted February 9, 2019 Posted February 9, 2019 Hi Andy, although the photos are not very clear (but pretty good for a general idea) I would suggest that the crack started at the 8-o-clock position (3rd photo) And progressed through the journal passing through the web oil drilling and then snap. If you look at that e=area carefully with a x10 glass you may see the start of the crack. probably in the journal/web radius. Nice paperweight Roger
toofast2race Posted February 9, 2019 Author Posted February 9, 2019 I’ll have a closer look. It’s done 13 years of serious abuse and a fair few over revs so I can’t complain - steel crank in the next engine.
Nick Jones Posted February 9, 2019 Posted February 9, 2019 Hmm, messy - but it hung on well. This seems to be where hard-worked 2.5 cranks break. The pics below are of one I acquired unknowingly as part of a spare short engine. It was free...... Ignore the rust staining - it had sat for a while. Anyway, the fracture pattern looked alot like I previously broke in my Herald 1300 and I showed that to a metallurgist who had spent many years working for a crankshaft manufacturer. He took one look at it and said "fillet radius not blended properly". He then showed me how the fracture surface was finest in one area against where the fillet radius met the journal surface and spread out from there becoming less fine until reaching the final gross fracture - probably 30% of the remaining area. Biggest source of fatigue failure in cranks he reckoned - by a big margin. That 1300 crank did almost exactly 20k with me and after it's last grind. Used to get revved to Smiths - literally. The crank above looks similar to me - see red arrow. On Andy's it looks like the crack may have worked around the radius to a greater extent, but I'm not seeing much influence from the cross-drilling. Reckon it was the bean counters stopped that.....
toofast2race Posted February 9, 2019 Author Posted February 9, 2019 The break looks like it’s followed the base of the radius - I think your right Nick - cross drilling not guilty - poor old thing
oldtuckunder Posted February 9, 2019 Posted February 9, 2019 Only from a layman's perspective I still prefer a 2ltr crank without a big hole through the centre of the journal! Alan
toofast2race Posted February 9, 2019 Author Posted February 9, 2019 This shows the value of regular oil changes ! You could eat your dinner off the internals
toofast2race Posted February 9, 2019 Author Posted February 9, 2019 33 minutes ago, oldtuckunder said: Only from a layman's perspective I still prefer a 2ltr crank without a big hole through the centre of the journal! Alan Can’t disagree with that- no fear of my 2000 doing the same
RogerH Posted February 9, 2019 Posted February 9, 2019 2 hours ago, toofast2race said: The break looks like it’s followed the base of the radius - I think your right Nick - cross drilling not guilty - poor old thing Hi Andy, as I mentioned in my above post and amplified by Nick. The crack has started at the 9-o-clock position in your photo and worked over to the right The very sharp line is where it went from cyclic to sudden failure. If you look at the segment you will see fine lines (beech marks). These appear with each crack phase. The radius may well be to blame. Any fine machining marks are stress raisers. But as on the TR4 crank there are also other forces at work. The big end journals 1, 2, 3 can flex across the main bearing. Big end #4 radius web takes all the flex as the flywheel is immovable. So #4 has twice the load. Roger
JohnD Posted February 9, 2019 Posted February 9, 2019 Wow! That was on the rear-most journal? That may be where vibration most affects it, next to the heavy flywheel. What's the story on the damper pulley? I know I'm biased/obsessed, but please may I have that (those? TF2R and NIck?) damper(s) to test? I have a small set of them, and as I have said, some of those deviate in a significant way, but none are from an engine that has suffered catastrophic damage in a way that could be attributed to lack of damping. A pulley is not a light item, and I'll be glad to pay for the postage, to me and back again, and to give you a report on it. I can't promise to return a damper overnight yet, but certainly within a week. TF2R, you said " I think I know why Triumph stopped bothering to cross drill them!" Did any Triumphs leave the factory with crossdrilled cranks? Surely yours was done at some later rebuild? The two drillings look to have different diameters, which would surely be most unlikely in the factory. And there seems to be a drilling concentric to the journal, perhaps to lighten it? Plugged presumably by a grubscrew, that explains the threads seen in the sides of that drilling. All this would have affected the balance and torsion characteristics of the crank, which might make testing the damper meaningless and academic, but I'm an academic now! Contact me by PM, please if you can help my research. Thanks! JOhn
oldtuckunder Posted February 9, 2019 Posted February 9, 2019 59 minutes ago, JohnD said: And there seems to be a drilling concentric to the journal, perhaps to lighten it? Plugged presumably by a grubscrew You can see the grub screw in the 4th picture, hense my comment about the big hole through the journal. I assume that it must be a fairly common 2.5 crank thing, as when I was having BE failures several people asked me if I had removed the plugs when cleaning the crank, but of course they don't exist in the 2Ltr cranks. Alan
Nick Jones Posted February 9, 2019 Posted February 9, 2019 5 hours ago, RogerH said: as I mentioned in my above post and amplified by Nick. The crack has started at the 9-o-clock position in your photo and worked over to the right The very sharp line is where it went from cyclic to sudden failure. If you look at the segment you will see fine lines (beech marks). These appear with each crack phase. The radius may well be to blame. Any fine machining marks are stress raisers. But as on the TR4 crank there are also other forces at work. The big end journals 1, 2, 3 can flex across the main bearing. Big end #4 radius web takes all the flex as the flywheel is immovable. So #4 has twice the load. Roger Quite a striking example isn't it Roger? Looking at the length of the break where it's followed the fillet radius edge around I'd say there must have been quite a marked edge there. John, Alan, There were some cranks cross-drilled by the factory. IIRC limited to TR5 and some of the MK1 PIs, possibly all long-backed cranks too? I think these will be the only ones with the concentric drilling blanked by grub-screw. Certainly all the 2.5 cranks I've seen (including the busted one in my pics) have been without, with just the same drillings as the 2L ones.
toofast2race Posted February 9, 2019 Author Posted February 9, 2019 John, the damper was a Shackford rattler, it had been on about 3 seasons. The flywheel was a 4kg all steel integral ring gear one after the engine spat off a 4kg alloy one twice (racetorations kit ) . Maybe once I got the flywheel to stop walking away from its 8 bolts ,the crank decided it had had enough! In my experience by the way, all TR5 and Mk1 PI are crossdrilled as are some early Mk2 and TR6 cranks - I have a short back cross drilled one in the boot of my car. Not sure about TR250? They have oddities - 2000 cam, simplex chain?
Nick Jones Posted February 9, 2019 Posted February 9, 2019 Short backed cross-drilled do exist then..... Show your machine shop the grisly remains to encourage them to make a really good job of that fillet radius!
toofast2race Posted February 10, 2019 Author Posted February 10, 2019 He’s such a grumpy bugger, 73 years old and retired but institutionalised in his machine shop that I’ll let it pass! It did see +7000 on numerous occasions!
JohnD Posted February 10, 2019 Posted February 10, 2019 Thanks, Nick & Andy, Learn something every day. J.
michaeljf Posted May 29, 2019 Posted May 29, 2019 Hello, My TR6 was built in October '68 and has no cross drilling or plugs.I have just started a major rebuild of the motor (which has a lot of upgrades including a Kastner S4 cam.) I purchased the car in San Francisco in 1994. Regards,Michael.
RogerH Posted May 29, 2019 Posted May 29, 2019 On 2/9/2019 at 7:42 PM, Nick Jones said: Quite a striking example isn't it Roger? Looking at the length of the break where it's followed the fillet radius edge around I'd say there must have been quite a marked edge there. John, Alan, There were some cranks cross-drilled by the factory. IIRC limited to TR5 and some of the MK1 PIs, possibly all long-backed cranks too? I think these will be the only ones with the concentric drilling blanked by grub-screw. Certainly all the 2.5 cranks I've seen (including the busted one in my pics) have been without, with just the same drillings as the 2L ones. Hi Nick, sorry for the delay. Here is a pic of a TR4 crank that has black ink Mag particle on white background coming from quite a long crack in the journal/web fillet radius. The crack goes over the top by quite a bit The black lines are at the ends on the crack in the pic. Roger
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