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The more I think of this tripps the more it's getting to me. Changing the type of oil isn't the solution.To be doing engine damage as you have suffered is not down to the make up of the oil it has got to be down to the amount of oil available at the engine & within the engine. As someone said in the past, the only way you can do a big end in in a newly rebuilt engine is for the engine to have been built incorrect, which I very much doubt, or oil starvation which I would agree with. Something drastic has changed on the oiling side, you have to back track, write down everything that changed up to doing the big end in & see if that throws anything up.

After seeing the old tank it was no wonder Tripps had problems, all sorts of things wrong with it, no deairation, wrong shape, pick up not in the centre, but hanst done any damage to the engine since I made him a new tank (is that right Tripps?) except for some breathing issuses which I think are bore problems ?

Great points people = thanks. Yes Mike the oil tank has been great and has pretty much sorted the starvation problem. The real pain the backside is the engines current want to spew oil out of the crankcase breather in vast quantities! This is really odd and lots of people I have spoken to are baffled!
Reading and taking on board all the great feedback I am thinking a switch to a semi synthetic oil would be worth a try as there will be no worrying over R being contaminated and will be interesting to see what happens. I have good access to Castrol products and am thinking their 10 / 40 semi synthetic maybe the one to go with. I am also going to replicate the breather set up used by the solo boys on their Rob Norths. I feel that this will improve things as the breather will then be pointing up hill rather than down and will enable me to run a pipe about 3ft long to the rear of the bike to allow the oil mist to be caught and drain back to the tank.
When we have run the engine stationary even blipping her and holding her at 3 - 4,000rpm or so we cannot replicate the breather issue. As soon as we go out on tack it happens but not always straight away and with varyong amounts of oil.

Trips your wellcome to come over and run her on my dyno if you would like to , it does not work the engine as hard as on track but better than blipping :d

Thanks very much Geoff. I may well take you up on that once she is back together. Would be nice to see what sort of BHP is being produced

Give me a call when your ready 07973479216 :d

Trips i see that the NSU outfit has twin oil coolers on,may be something to think about

Dick is right, diesel oil is made like the old oils. Got to remember 30 odd years ago there were not many oils to use. Match the age of the engine to the oil you use, all synthetic oils are made for closed crankcases, so do not absorb water, if you use it on an open breather the water that condenses inside de-grades the oil. Also too synthetic oil can make wet clutches slip. As you said before you had no problems with R, just a bit expensive, but cheaper than re-builds.

Triplebrew,
I am the worlds greatest fan of R there aint nothing like it and to disagree with a previous there is no synthetic which has the " shear" strength of castor,however its no benefit in a plain bearing engine,R is best used in roller engines as rollers will try and fling off the oil,castor sticks like you know what to a blanket,in a roller bearing engine its more need to have "presence rather than pressure" in a plain bearing engine pressure is whats needed.
Now here`s where I get the p**s taken,all the years we raced Triumphs in sidecars we used good old Castrol GTX 20/50 and dumped it after every 2 meetings...
OK let me have it!!!!!!

Good words peter. Over the years I've tried most oils, rotella, R, synthetic, semi synthetic etc etc. I happened to settle with a fully synthetic but then I run an oil pressure of 125psig in a motor with plain big ends so with that pressure the oil gets its way into every nook & cranny. As I said previously, everyone has their favourite, it's all down to what gives you the confidence. But, for tripps to do a big end in the first run after the rebuild isn't down to what the makeup of the oil was but down to the lack of oil at the big end. Hopefully Mike has cured this problem with the new oil tank. We can & most probably will debate this till the cows come home but, go with what you feel is right for youe engine.
I dont think tripps is running a belt drive so he is running a wet clutch so in that case synthetic is no use to him.

For a good number of years we ran Duckhams 20/50 in the Triumphs with few problems attributable the oil itself. I was recommended latterly to Castrol 351 for pre-unit ARE 750 motor and found it faultless in all ways. Needs warming up thoroughly as when cold it tends to go round in lumps but when hot - superb!

351 was apparently developed by Castrol for F1 cars - Castrol were surprised that some sidecar crews were using it as it was intended for water colled engines. Some further research by the company showed that it was also ideal for heavily stressed air cooled four stroke bike motors.

Just my 0.02 euros worth ....

Blimey what a monster thread this is becoming
We are running a standard chain primary drive with a dry clutch. Looking at the original Triumph manual a 20/50 oil is mentioned. However having sought lots of feedback I still feel a 10/40 semi synthetic is the way to go. Part of me says to go back to R as we never seemed to have any problems but maybe we were either lucky or the R was masking the short fallings? Also this would require a real strip down down and clean to be confident of no future problems.
So what I am looking at doing is trying out Castrol GPS semi synthetic in a 10 /40 grade and see what happens. Geffro has kindly offered the use of his dyno so we shall take advantage of this and see what happens.

Tripps, if it's a dry clutch how are you lubricating the primary drive?

The primary drive is the standard triplex chain which sits in an oil bath. The clutch is based on the Mini Cooper and is a single dry plate set up behind the primary drive. I hope that makes sense