Crankshaft

[new to this]

What do they mean,when they say crankshaft reground and cross drilled,the cross drilled is the bit i don't know about

thanks Dave

[Motorsport Micky]

The crankshaft has drilled internal oilways zig zagging down the length as in and out from main bearing journals to big ends to main bearing journal etc which carry pressured oil to the various bearings. This cross drilling is normally part of the initial manufacture of crankshafts from the makers although sometimes on competition cars additional drillings (or even restrictors if flow is too much) are carried out to improve the lubrication.
Reground obviously means the bearing surfaces mains and big ends have been reground to a new smaller dia (normally in variations of -10 thou 20/30 etc) because the bearing surface has imperfections in it (grooves etc). The mains and big ends are always ground the minimum amount to preserve crank life so it's not unusual to find big ends ground but the mains the original size or vice versa although they would be unlikely to grind individual bearing surfaces ie only grind one of the set of mains or big ends.

Micky

[new to this]

Micky

thanks for the reply

Dave

[Mark Serj]

Other than crank regrind / replacement of bearing shells, can I ask if there is any worthwhile improvement type work that can be carried out when the crank is out of the motor please? Am I right in thinking all Stag cranks were 'cross drilled' (as opposed to some other form of lube channel) from the start?

Thanks in advance

[Motorsport Micky]

I take it you are not planning an advanced sort of Motorsport so the standard preparation as per Triumph with drillings etc should be fine but take care to have the crank rehardened if grinding the journals big ends or mains.
The surface finish on most cranks in cars are of the "skin" preparation ie normally only a max of maybe 30 thou deep, and on the Stag it was merely spat on by a passing engine assembly worker sucking a Fishermans friend !
So for any grinding I would have the crank "nitrided" or "tuftrided" (Google them) as a matter of course which helps preserve the bearing surface in use.
Just a word of caution, it's not unusual for the crank to bend, it happens to many cranks and is easily sorted by the engineering shop who ground and hardened the crank for you (take it to the same place). I had a crank develop a severe bend from centre journal to the end, took it back to the prep shop and they reset it within 48 hours back to straight (they hit it with large hammers, the trick is where), used it for 2 years motorsport and it was still unworn and unbent at the end of the season.

If you build the engine yourself fit the crank in stages checking in case any deformation has occurred, after every fitment of a part check to make sure all is spinning easily. If all is well and the crankshaft is true there will be no discernible stiffness or locking up, the crankshaft will obviously get stiffer as more bearing surfaces are clamped onto it but what you need to find is the unacceptable jump in effort after fitting or clamping a bearing cap which shows a problem is in that area.

Oil the bearings in their journals and place the crank in their cups, no caps. Spin the crankshaft with fingers only, it should spin, inspect each journal bearing and the oil being smeared from each, they should all be touching and having oil distributed onto the crank evenly, if not keep an eye an the offending journal.
Check end float on the crank and fit thrust bearings to control within limits, spin the crank with fingers only, it should spin.
Bolt on the caps with oiled bearings from the centre outwards one cap at a time hand tight, no torque yet, spin the crank with fingers after each cap is fixed on, it should spin.
Then take up the torque on each cap in turn I do it in two stages (varying on different engines) and spin the crank with fingers only in between each torque, it should spin.
I do it for race and road engines the same, although because the engines are for my own use the paranoid checking and faffing about doesn't bother me, if I had to make money out of it that would be a different story.

Micky

Then you are into the hardware throughout the engine

[Guest]

Am I right in thinking all Stag cranks were 'cross drilled'.
Thanks in advance

No Stag crank was ever cross drilled.
The only late 60s cranks ever to have this treatment were some rare 2.5pi, the TR5, & the very early TR6, but they were not high grade material, so need to be tufftrided, which gives a few microns tough skin to the surface.
They then have to be carefully polished.

Here is a non x-drilled early Spitfire where I have just polished 2 of the mains, to show how it looks before/after treatment.
cranky1.jpg.
These are quite capable of being run at 8500rpm+

You can see a cross drilled crank from those days, because it has allen plugs in the galleries, which can be removed and a brass restrictor in one of the oil ways.
Here's one with a plug removed..

crankT2.jpg

If you ever regrind one of those, then tufftride it, you have to remove the gallery plugs, which is not a fun job, clean it all out, then PEAN OVER the holes with the brass gallery plugs, because they come loose thanks to the 525C tufftride process.
(Ask me how I know!).
Nearly all old XK Jaguar cranks were cross drilled, I suppose because the oil system was so crap from the factory for such large engines.
Taking gallery plugs out of a 4.2L E type crank is a HORRIBLE JOB!

The only real steel crank to be cross drilled were the very early Dolomite 16V, which were made out of a nitriding steel called EN40B, as they had competitive motorsport in their sights, and had to homologate it.
EN40B cranks don't need to be rehardened because the lengthy nitride process goes as deep as 0.030".
However I don't think I have ever seen one that wasn't totally wrecked!

Cross drilling is really not advised for a normal engine with lengthy service intervals, or with inferior quality bearings, for the simple reason you get a fairly massive drop in pressure internally in the crank.
This manifests itself with pressure as low as 30psi when HOT at 2000rpm, depending on how the crank was ground and the bearings used. (I see this problem with Clevite 77 which have extra clearance compared with VP!).

Most people don't realise, the only real solution for the Triumph engines is to take special care fitting the highest possible engine bearings (copper-lead-indium), not steel backed aluminium, get the clearances right, and lastly but most importantly to increase the oil pump capacity to the maximum possible.

This is no mean feat, as practically all the remanufactured bearings and pumps are highly inferior to the original Hobourn Eaton ones, and don't come even close to spec even when using synthetic oil.

The bearings are yet another of those thorny subjects best left for another day.

[Mark Serj]

Cracking advice Micky - many thanks. I'm sure there are others who will appreciate this as well.

Cheers

Mark

[Mark Serj]

Thanks also for the illuminating info from Down the plug hole as well!

[mjheathcote]

I 'tear dropped' all the oil feed holes on the crank and hand polished afterwards before fitting.
Also had everything dynamically balanced.

[Mark Serj]

Hi Mike,

Can you elaborate on the tear dropping please? When you say hand polishing, do you mean the bearing surfaces of the mains and big ends? This must have been quite a task on a (potentially!) hardened surface?

Finally, to make the most of the dynamically balanced crank, did you equalize the weight & achieve the same c of g of each rod & piston assy?

Best Regards

Mark

[Guest]

Finally, to make the most of the dynamically balanced crank, did you equalize the weight & achieve the same c of g of each rod & piston assy?

STOP WORRYING.
If you want your crank balanced take all the rods,pistons, crank and pulley+clutch and flywheel into Andy at Bassett Down.
Ask him to balance it all inc rods and pistons, polish the crank once it's been properly, nicely ground and tufftrided.

PAY.
Don't bother with anything else, don't try to do it yourself.

There are people you can trust, and lots you can't.
Andy is the BIZ for V8s, and you can tell him I told you so.

[Mark Serj]

I wasn't worrying, just curious, like what us Aerospace Engineers are......

[mjheathcote]

Hi Mike,

Can you elaborate on the tear dropping please? When you say hand polishing, do you mean the bearing surfaces of the mains and big ends? This must have been quite a task on a (potentially!) hardened surface?

Finally, to make the most of the dynamically balanced crank, did you equalize the weight & achieve the same c of g of each rod & piston assy?

Best Regards

Mark

Tear dropping is radiusing all the oil feed holes after the crank has been ground, so no sharp corners. Afterwards polishing the bearing surfaces with very fine emery cloth.
Engine balancing I sent the crank, front pulley, flywheel, pistons and rods off to a specialist for balancing.

[Stagdad]

STOP WORRYING.
If you want your crank balanced take all the rods,pistons, crank and pulley+clutch and flywheel into Andy at Bassett Down.
Ask him to balance it all inc rods and pistons, polish the crank once it's been properly, nicely ground and tufftrided.

PAY.
Don't bother with anything else, don't try to do it yourself.

There are people you can trust, and lots you can't.
Andy is the BIZ for V8s, and you can tell him I told you so.

Just googled them, nice and handy for me just a few miles away.

What would be a ballpark cost for this sort of work?

[Guest]

What would be a ballpark cost for this sort of work?

No idea, it costs what it costs.
However the difference in running of a fully balanced Stag, compared with a vanilla one has to be seen to be believed, (despite the labyrinth inlet manifold).