Britbike forum Forums British Motorcycle specific Brands Triumph bulletin board Torque Wrench settings

Hello again Trumpeteers, hope nobody's had a spill since the last time I was on!

Do any of you guys know the torque values associated with a 1957 Triumph pre-unit 650 bottom end fitted with an alloy Bonneville head? I have the old manual which is a bit vague and I've read some articles where the values differ.

There also appears to be different ways to tighten the big end caps. Do people still stretch the con-rod bolts .004" - .005" or is there simply a pre-loaded torque setting these days?

I know there was a change when the con-rod bolt thread changed from 5/16" cycle thread (26 tpi) to 5/16" UNF (24 tpi) but even these appear to vary from builder to builder.

Keep scratching. Maddoman

Stretch beats torque everytime if you have the stretch figure, the factory got the torque figure by measuring the stretch and seeing the torque needed, so if you do not have exactly the same conditions as the factory then your stretch will be wrong. Its also means the thread form can change and you still get the stretch right by measuring it directly.

Use both together, especially helpful when re-using rod bolts. If the stretch you've measured at the torque figure specified exceeds 4-5 thou, can those bolts and get some new ones.

Cheers,
Bill

As Kom said, the torque figure is subject to so many variables, the extension should be used, which is directly related to the stress in the bolt.
This is subject to the caution John Healy and others have mentioned about quality of rod bolts supplied these days.
I must say that over 35+ years, and replacing the bolts maybe 4 times, always supplied by Kays of Ealing in the early days, more recently by TMS, I've not experienced any problems, but I'm not a boy-racer these days.
As HT says, it is a good check to monitor the torque (even though it in itself gives no definitive information) if you notice abnormal extension with a modest increase of torque, this could indicate that the bolt's elastic limit has been exceeded. This would be a potential catastrophic failure.

Hi Guys, Interesting about the rod bolts.

The bolts were reduced from 3/8ish to 5/6 at a point in time. About 1968-'69. Triumph put out a service bulletin covering this change with revised torque. Which is lower for 5/16

Recently did some experiments with '69 Bonnie rod bolts 5/16-24 lock nuts. The wrist pin bushing cam loose on left rod so it was junk. Unable to find good used rods so got new LF Harris rod weight matched set.

So we had 2 rods to play with. Using new Snap-on dial type torque wrench which is the most accurate they sell we compared torque to rod stretch.

So start with, not that easy to get repeatable readings of length with Vernier caliper due to the end of bolts is not very flat. Even with micrometer not as easy as I'd hoped.

The large bolts had a spec of 28# while the smaller is 22#.

I have no personal experience with the large bolts or measuring stretch on those.

However on the Triumph original rods on the '69 Bonnie, the bolts have very little stretch at all. I could only measure maybe .001-.002 at the very most. This alarmed & puzzled me. To get .004 the torque was upwards of 30# which is really cranking down. Again hard to measure accurately.

The Harris rod is forged a slightly different shape. More beefy at the big end where it blends to the beam. This indeed makes the rod a little heavier.

Harris bolts are similar, but slightly different in the waist. Harris lock nut are very different being like a conventional pinched type like you find in hardware store or on rest of bike.

Triumph lock nut has the round top with the slot. I have no idea which is better if it matters, but we used the Harris nuts on final assembly. Used non locking nuts to pull on caps as the caps on Harris rods are a tight fit on the Harris bolts.

Measuring stretch of Harris bolts showed >.001". Again this puzzled & alarmed me. Checking with some builders they found this as well. So, we left them at 22#. As a back up I used loctite 243 on rod nuts. I know it probably doesn't help but it made me feel better.

Harris bolts are rougher on both ends making accurate measurement even more difficult. Truth be told I never got repeatable measurements as I would have liked. But not even close to .004" stretch. I measured nut loose, then opened calipers .004 & there was a large air gap so if it stretched, not much.

Back in the day we didn't have measuring tools & just used torque wrench without problems.

The '69 Bonnie motor has now covered 400 miles to good results. It is fitted with oil pressure gauge & pressure has not changed so it seems all we be well long term.

I still ponder bolt stretch or lack of it though. So I have no answers, just more questions.
Don

A diesel mechanic I know well informs me that the rebuild manuals he has used specify measurement of bolt stretch as the preferred method.

EACH bolt must be measured BEFORE installation, as a check against slight length variations.

The stretch measurement is the best way to go, but bear in mind that it means little unless you're confident of the quality of the bolts. There's been a thread recently on the owners club forum started by a member who bought new bolts, fitted them using the stretch measurement method and then double checked with a torque wrench. The torque wrench only got to 14 ft/lbs before it clicked. The bolts, it turned out, were Wassell shite. Goes to show how bad some pattern stuff can be.

ARP stuff is pretty good. machined both ends, so you can measure the stretch consistently.

"The torque wrench only got to 14 ft/lbs before it clicked."
The bolt extension is the only reliable number, assuming proper tensile bolts. Of course, if they are elasticated lead bolts from Narnia, this doesn't help.
But considering the recommended torques are in the 20's of ft/lbs DRY, 14 may not have been so far off if oil was on the threads?

I think the explanation is closer to the poor quality steel than anything else. .004" to .005" stretch was achieved which, if previous posts in this thread are anything to go by should equate to more than double 14 ft/lbs. There are some rubbish quality pattern parts about.

If you are going to use the bolt stretch method, and expect accurate results, you will need to face both ends of the bolt off with a grinder. We use the valve refacing machine. On one end there is stone used to face the tip of the valve stem. We use this to face both ends of the rod bolt perfectly square. Given that the thread end of most rod bolts are anything but, true and square, it would be almost impossible to get an accurate reading. If you ends are perfectly square forget what I said.

^^^this is how i do it.

ARP bolts and a fairly inexpensive stretch gauge. the ARP gauge is like US$200, but this one from JEGS or Summit was closer to US$50. i'm very careful with it, and so i think i'll get by.

these rod bolts have seen more than 9000 rpm, so they've been good so far. i might should swap them out just to be safe, stretch or no stretch.

Note that the ARP rod bolt ends are faced perfectly square to allow for you to use a micrometer, they also have a dimple on the same face to accommodate the the dial indicator's point and "tit" as shown in the picture above. Without the dimples at both ends of the bolt, for most people it would be easier, and more accurate, to use a micrometer. If you are on a budget, and cannot afford both, a micrometer would have more uses.

I believe they were always the same diameter, the thread pitch was changed?

....I think fussing with a stretch gauge on old rods with old bolts being installed on a crank journal that was not ground to fit the bearings torqued in the rod is not worth the effort....I should use a stretch gauge on my race Triumphs but I just use an old bending beam torque wrench...

Hi Hillbilly, Thanks for pointing that out. I think I was in error. Looking at my notes I think I messed that up. I can't seem to locate the photos of the 2 versions.

While at Rabers looking a numerous used rods, the early bolts had a dia. of .335". These take 28#. I don't know the thread pitch if CEI or not.

The later bolts had a smaller neck. I'll have to dig an old one out & measure it. These take 22#.

My notes say they torque changed eng # HC23445. However looking at service bulletin they identify a nut change identified by color of nut for 22#.

Doing some experiments with plastigage & new rods, it took almost the full 22# to get full bearing crush.

Testing with plastigauge with old rods, over torque did not change crush or clearance.

I do not own a bore gauge for checking rods.

Going off thread, but related to rod bearing crush, clearance.

The new rods & shells gave .0005 less clearance. With new rods & inserts the clearance was .0015 according to plastigage. Plastigage was new fresh stick. Oil pressure fully heat soaked after a few hours riding is 17-20# idle, 70# 3000rpm. This is 69 Bonnie. With stock later tappets short oil flat. The prior owner had installed metering dowel with a pin in it. The left end of dowel (installed) had been gas welded shut. Is that normal?? I don't know. The oil pressure prior was 30-35# idle, 90# reving. The pin looked like it restricted flow to PRV. I think that explains high pressure reving. But idle I don't know. The bearing clearance is now less. I installed hollow dowel. My thought was tappets could use the oil.

It seems a fair amount of oil is lost via tappet lube. The oil pump & PRV were not changed so I only can account for change due to hollow dowel. I always wondered oil volume to tappets effect on oil pressure. How many cc per minute that might be I don't know.
Don

Don, I know some experienced guys here say if you have nitrided cams, run oil with enough ZDDP, you can delete the exhaust tappet oiling...I think Triumph did delete it towards the end?

I don't fully understand the need for the exhaust tappet oil feed.
As HB says, it is assumed to be related to hardening, or not, of the cams.
As far as I know, earlier bikes (both pre and unit) didn't earn a reputation for cams wearing prematurely.
Yet something at the tail end of the 60's/start of the 70's seems to have raised it as an issue, to such a degree that is was deemed necessary to make a significant change to the oiling system of old.
What I find curious, is that when this change was made, (to enhance the lubing of the ex cam) nitrided cams were already in use.
And as HB says, such lubing is regarded as unnecessary with nitrided cams by general consensus.
So why did Triumph introduce this lubing at a similar time to nitriding? Belt and braces?
Something must have provoked it. I wonder if it may have been the change from oil-fed rocker pushrod balls? Just a thought thrown out.

According to my not too reliable memory, the pressure fed exhaust tappets were introduced in the mid 60's as a stop gap for premature cam wear. When that didn't fully fix the problem, they went to the hardened cams which nearly everyone was already doing anyway.

And pre units have some issues with early cam wear, too. I always fit a nitrided came to any engine I build and if it has the pressure fed tappets, I block off the oil way. No need to sacrifice some oil pressure; keep it all for the crank.
And less chance of oil leaks, too.

Cheers,
Bill

Triumph ceased the pressure feed to the exhaust cam in 1981. I still kept the oiling to the ex. cam on my( '76 T140, '76 T140 engine spl.) road bikes, but I have blocked it off in my race project. ( '76 T140 ) That is using Megacycle cams.
Nitrided cams were introduced in 1969, from engine number DU 87105, but the oilfeed was kept.

HT/Tri - best as I can gather so far is the oil fed tappets came in ~67-68, then nitriding in 69.
I wasn't aware of the soft cam issue in pre-units, though my close personal experience of them only amounts to 3 of my own, I must bow to the much wider experience of yours! All I'd say on that is that by definition, pre-units are older than units, so finding cam wear in them may not necessarily be premature?
I've not heard of endemic camshaft failures of pre-units "in the day", whereas the actions taken by Triumph in the late 60's were presumably in response to problems showing up within a year or two of purchase, wouldn't you suspect?
I don't think this can be explained by mileage per year or severity of use in any simple way. Certainly in the UK, bikes in the 50's did large mileages, as cars were not owned by most, and this was the golden era of thrashing these bikes beyond (not within) an inch of their lives!
I suspect there may be an interesting engineering story in here, perhaps? Dave

Koan, I'm certain '66 was when the tappet oil feed was introduced.

Thanks Tri, I don't know the units in detail, so it was a ~approx.
Still, I find it interesting that similar cams had been used for quite a number of years, without creating one of those legends (like Combat main bearings, CSR cranks, indeed Commando camshafts, etc) that has never come to my ears.
I can't help thinking that some other change (and it could be a subtle one) brought to a head the need to do something.

A cursory look at how cams an tappets get lubricated will show how the exhaust cam has a hard life in all twins, not only from the extra heat but from the reduced oil splash they get compared to the inlet.

It would be a safe bet to say that a huge percentage of bikes that came to California were hopped up. One of the hop ups involved shaving the base circles of the cams to get more lift and installing stiff springs.

That and high compression pistons. And punching them out as far as they will go. (I've seen + .080 in pre units which is just plain stupid. Instant hot rod bike.

Sort of. They had a reputation for going fast but not for long.

Cheers,
Bill

morgos don't even have the drillway. my 72 has run a hard-faced megacycle cam without pressure feed for over 30 years.

as soon as i blocked off the hole in the cases my oil pressure light stopped flickering at idle.

30 years.....Longest I had a bike is 10 years and only because it was in my living room most of the time..