So that's why the oil presure was low ......!

[TedTaylor]

The oil pressure of SCG (the Mk1 PI estate) has always been very low though it did not rattle or knock, and pressure had been increased to a workable degree after Jonathan Lewis and I discussed the problem and I tried some SAE 30-75 oil which did pick things up to a workable level.

Because Gordon Townley (from the Wyedean Group) has entered the old girl for the RBRR we felt that we would have a look at the shells and see if we could get away with simply reshelling or whether more drastic was necessary. The hope was that we could just re-shell because it would give me more time to work on AFH which my brother Phil and I are using on the event.

I think the attached photos of the lower shells (apart from no 5) tell it all!  ??) I have never seen a pair of shells quite like No. 5 where the bearing material has squeezed out round the sides of the big end itself!

Although I have not checked the tolerances on the original crank I don't think I will bother even though amazingly scoring is minimal - I had acquired a suitable crank already from Mark Swingler 'just in case'.

So it is out with the engine and a full rebuild - I have all the kit to be able to completely refurb. the head etc. so may as well do it.

MUT

[ferny]

I melted one around the conrod once ;)

[DougBGT6]

Yes, mine were like that after my ex-wife failed to notice the little red light. Well, it was only a small red light, something serious should have a much bigger light. Right?   :-/ :B :B

[thescrapman]

It started a RBRR like that, and would probably have finished it but for the rocker shaft screw....

Bolt it back to gether and away you go... :-)

[Richard B]

1526 wrote:

I had acquired a suitable crank already from Mark Swingler 'just in case'.

The replacement crank is a cross drilled one, isn't it?

[TedTaylor]

Richard_B wrote:

The replacement crank is a cross drilled one, isn't it?

Nope.  Getting a good cross drilled crank is difficult.  

Also from the reading that I have done and comments (verbal and read) from people who have cars with cross drilled cranks there is little or no value in fitting one.  Because of the two outlets per journal you need an oil pump in tip top condition capable of dealing with the greater flow required with the cross drilling, and the pumps in the TR5/Mk1 PI engine to which they were fitted in having a normal six cylinder pump could not cope with the flow once the pumps started to wear and hence the apparent habitual oil flow problems on even marginally old engines.  A blue printed pump would obviously help with the flow problem and maintain oil pressure better over time.

I have not checked the tolerances on the original crank yet but the big end journals are already on 30 thou and may need an extensive grind to get them back within specification.  I have found that 40 and 50 thou (and even 60 thou) shells are available but this level of grind does worry me hence having the TR250 crank (or another good cross drilled one) available is an essential standby.  Any TR250 crank would have had an easy life in a low stressed engine, and the one I have is to all intents and purposes showing minimal wear (just one main that is close to limits).

I will mull over a regrind on the old crank and may even cross drill my replacement (it is a fairly straightforward operation with the right kit) PURELY for originality ........ unless someone has a decent original cross drilled crank they want to do a deal on to save me the hassle of cross drilling my TR250 one..........

MUT

[Richard B]

Ahh learn something new everyday. I did not realise the TR250 crank was not cross drilled.

I'm waiting to rebuild my PI engine for the saloon. It has a MkII 2500 temporary installation at present.

[andy thompson]

1526 wrote:

Nope.  Getting a good cross drilled crank is difficult.  

Also from the reading that I have done and comments (verbal and read) from people who have cars with cross drilled cranks there is little or no value in fitting one.  Because of the two outlets per journal you need an oil pump in tip top condition capable of dealing with the greater flow required with the cross drilling, and the pumps in the TR5/Mk1 PI engine to which they were fitted in having a normal six cylinder pump could not cope with the flow once the pumps started to wear and hence the apparent habitual oil flow problems on even marginally old engines.  A blue printed pump would obviously help with the flow problem and maintain oil pressure better over time.

I have not checked the tolerances on the original crank yet but the big end journals are already on 30 thou and may need an extensive grind to get them back within specification.  I have found that 40 and 50 thou (and even 60 thou) shells are available but this level of grind does worry me hence having the TR250 crank (or another good cross drilled one) available is an essential standby.  Any TR250 crank would have had an easy life in a low stressed engine, and the one I have is to all intents and purposes showing minimal wear (just one main that is close to limits).

I will mull over a regrind on the old crank and may even cross drill my replacement (it is a fairly straightforward operation with the right kit) PURELY for originality ........ unless someone has a decent original cross drilled crank they want to do a deal on to save me the hassle of cross drilling my TR250 one..........

MUT

The "original" drilling on the B/e journal should have brass restrictors which are literally pin holes compared to the normal drillings. Granted the crossdrilling is a compromise if poorly maintained - they are prone to sludging up and then depositing the sludge into the shells at inopportune moments wiping them out.

Pressure may be a bit lower but the shells and pump would need to be well worn to lower it past say 15 at idle and 50 at speed.

One of the the issues with the cross drilling that Andy Roberts once spoke of is that if poorly done you get a stress raiser that can propagate as a crack and end up as a snapped crank.

[Ridgetone Triumph]

Many years ago when the early TR's and the early MK1 PI's gave up their engines for races cars (due to unforeseen crashes) it was found that the cross drilled cranks were as Andy says 'development issues'. We found this on the ones for or built for racing, best to stick with a non X-drilled job for high performance. For normal use the original will be fine  ;) This is my two pence worth  ;D
I see there is a crossed drilled crank on the net for sale?

[TedTaylor]

This tends to reflect the comments I have come across as mentioned previously and is why I will not worry about using the non-cross drilled crank if I have to.

I have had a good look at the crank and while the other journals are really not too bad and could possibly go again at a pinch No.5 is decidedly the worse for wear. ??)  See photos though they have lost some definition in being reduced
Without using plastigauge it is difficult to accurately assess the depth of the grooves in the crank but I suspect they will exceed a 20thou regrind.

The comment on the 'crooked camshaft' ;D, if that is what is being referred to, has been covered previously and on the Big Saloon section of this Forum.  I have spoken to the seller and it would appear that the crank is a possibility if I wish to keep a cross drilled crank for originality in what is a very rare car, so feel obligated to take a chance and go for it if it does not get too expensive  :-/

MUT

[ferny]

Here's the bearing I mentioned.

Late night + wine + very early morning + 100 mile commute = "oh bugger"
Also bent a con-rod when the piston hit the cylinder head...


Make you feel any better about yours?  ;D

[TedTaylor]

ferny wrote:

Here's the bearing I mentioned.

Late night + wine + very early morning + 100 mile commute = "oh bugger"
Also bent a con-rod when the piston hit the cylinder head...


Make you feel any better about yours?  ;D

Just a bit   :-/

MUT

[piman]

Hello Ted,

" Because of the two outlets per journal you need an oil pump in tip top condition capable of dealing with the greater flow required with the cross drilling,"

That does not seem very logical. there is a long drilling prior to getting to the big end journal and the clearance in the journal itself, which will be the majority of the restriction, I can't see that doubling the area for the last little bit makes that much difference?  I understood that the idea of cross drilling was to give a more consistent oil supply. It follows if that does work it will take more oil but not as might be imagined, a substantial amount more?

I'm also sure that when the designers did the design that oil capacity of the system would have been carefully worked out

Alec

[TedTaylor]

Sorry Alec I have to disagree with your argument.

While you are correct about the long drilling prior to the journal, when it gets to the big end the main resistance is where the oil has to force itself through the miniscule gap between the journal and the shell so that the two are separated by a very thin oil film.  The effective cross sectional area of the drilling is much greater that that of the oil film between the big end shell and the journal, and while the area around the journal/shell is large in comparison its height is extremely small - in the order of a thousands of an inch or less.
Two journal drillings will double the effective cross sectional area.

The best analogy is a reversal of the explanation that I used to give the children I taught Physics and Technology to where I used to use water flow in a pipe to explain electrical flow.
Think of it as electrical flow where the hole through the crank is the cable and the miniscule gap between the shell and journal constitutes a high resistance.  
If you have a cross drilled crank you have to all intents and purposes two resistances in parallel and double the flow potential, and the limiting factor in maintaining the flow through the pair of resistors (journal/shell gap) is the ability of the current source (the oil pump) to maintain the flow through the resistance provided the diameter of the conductor (the bore drilling) can maintain the level of flow required.

Bearing in mind the cross drilled crank as far as I am aware was only used on the TR5 and Mk1 PI, being dropped for the TR6 and Mk2 PI (apart from a few at the start of production), and cars with cross drilled cranks are more prone to oil pressure problems as wear occurs, it does suggest that the designers did not have things properly worked out.  
After all much as we love our Triumphs how often have we cursed aspects of the design of the cars for lack of proper development. :-/

MUT

[andy thompson]

Hence the brass flow restrictions on all the x drilled cranks I have ever seen?!

[piman]

Hello Ted,

Put some figures (guesses) into your equation.

60 plus ( 5/5) plus 100 =162.5 double drilled.

60 plus 5 plus 100 = 165 single drilled

With those figures that is a small difference but I don't think that they favour my theory particularly, certainly the highest resistance in a sound engine is the journal clearance.
I would add that when I built my engine I was worried by the high oil pressure, particularly cold and I had to pack the oil pressure relief valve using a convenient Dowty washer. 45,000 fairly hard miles later it still maintained the original oil pressure.

Alec

[piman]

Hello Andy,

I have only ever seen one, that is mine and it has no restrictor (I'm assuming you mean an orifice?), however it has a brass blank at 12 o'clock where the main drilling from the main bearing journal to the big end journal, ( i.e. the outlet if it were not cross drilled) is blanked off diverting oil to the cross drillings.

My basis for choosing a cross drilled crank is on GT's tuning manual as it's benefits are, quote,' better lubrication to the journals, and a lighter flywheel.

He did say that there is slightly less oil pressure and mentions blue printing the oil pump. (Presumably I did, I forget as it was so long ago?)

Alec

[Richard B]

All interesting.

I alway had the change to the non-crossdrilled crank as another, cost accountant inspired money saver.

The crossdrilled crank I have here, does not have any restrictors on the cross drilling (If thats where you mean?)

[andy thompson]

I need to get a picture of one of mine - btw my MK1 x drilled crank has given no issues over the last 12 years or so and has seen plenty of high revs and abuse. I have reshelled it twice but always only precautionary. Oil pressure 15-20 psi very hot idle - 50-65 very hot running.

[piman]

Hello Richard,

"I alway had the change to the non-crossdrilled crank as another, cost accountant inspired money saver"

Something GT mentions in his book about several components.

Alec

[Nick Jones]

Oil pressure shouldn't be affected by cross-drilling unless the bearing shell/crank clearance is excessive anyway.

Nick

[TedTaylor]

After all the various dramas of crank and camshaft I now have everything back ready to do the rebuild.  

Crank reground, tuftrided (the old one was not done despite a 30 thou b/e and 20 thou mains regrind which probably explains its state after only 50k miles), balanced, sets of the new Revington VP2 spec shells after the pointer from Andy Thompson.  

New pistons - in the end as was suggested by Richard Brake it proved impossible to get the County pistons to match up to the original Stanpart ones, and even the ones that I acquired from Mike Stevens and Craig Pattinson (though thanks to both) proved a problem after they were cleaned up.  So despite the old pistons being in superb condition I bit the bullet and bought a new set from Chris Witor (CW).

The camshaft problem was resolved.  Thanks to a 'heads up' from Nick Jones I acquired a very nice one from CW along with new cam followers.  

With Gordon acting as the chauffeur (his car was much more economical for the trip to CW) I eventually succeeded in spending a small fortune with him on the necessary final engine and suspension bits.  

Mind you I had yet another problem few weeks ago when checking the head ready to refurb and finding firstly that seats needed recutting which is not a problem in itself because I have a full set of professional Neway cutters, but secondly it was not the correct head for this period car!  Cursing I went into the 'stores' (one of four sheds actually) to kick a few things around in frustration ........ and uncovered a spare head which when I checked the number against CWs list it turned out to be a correct one for my period engine!  Mind you in a bit of a state from wear and storage but a few days of loving care have sorted that.

While the front suspension was off it was sensible to do something about that rather rusty load of metal while waiting for all the engine stuff to be done.  All painted and refurbed and waiting for assembly.

There are no doubt other things which I will find that I have overlooked but the great assembly session with Gordon's help is about to start.

Luckily I have just sold my Overfinch engine and box for good money and blew all this on the crankshaft work and with CW, though there was a bit of light relief.  
When I collected my 'restored' crank from the engineering company I asked about the original kn*****ed crank that I had taken in and had asked them to see if it could possible be restored in case someone could make use of it.  The guy who does the work came out and confirmed that he felt it would actually go again (though it will be on a 40 thou mains grind at least which I had been advised was not good), and as he had a GT6 wanted it for that engine so offered me £100 off the bill - which bearing in mind the replacement crank off ebay only cost me £27 was hastily accepted!

Pictures later.

MUT