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rogerguzzi

Duplex Cam Chain Alignment

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18 minutes ago, Nick Jones said:

Offset PB bushes are used for the A-series rockers to get to 1.5:1 (they start at 1.42 IIRC)

http://www.jonspeedracing.co.uk/index.php?webpage=product_detail.php&product_id=14473&cID=13895

Dunno if their rocker shaft diameters are the same as ours....... could save some work?

Nick

Hello Nick

                Ours do not have bushes! so need to be bored first so may as well be bored offset?

Roger

ps the timing was driving me mad today I did it John,s way(triumph) and checked another and got different readings?

Seems clear now i have had the vino! or not! still all day tomorrow?

Roger

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Hello All

              I measured an old camshaft and it is 0.240" so take off 0.010" clearance = 0.230 x 1.45 = 333 not the the 0.350" as in all the charts

But I will still have 0.050" more lift so I suppose it is all relative?

I had another go at the valve timing and if I did not know different I could swear I have a hunting tooth as in my Velocette KSS 350 OHC

I check it one way and it is close then I try another way and it seems different!

So I gave up as the post man delivered a new Woodruff key, so I thought I would fit the front engine plate properly.

But when I came to fit it it is wrong its 0.200" wide and should be 0.187 and supplier said they are all the same in his stock!!!!(I wish I could find the old one)

So I decide to fit the rear seal and engine plate but I noticed and arrow on the plate and wondered why Triumph stamped it there?

Has anybody got a supply of Woodruff keys and want to sell one?(the one supplied was as rough as a Bears Ar*se) looked like it had been flame cut and only the sides ground.

Roger

 

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4 hours ago, rogerguzzi said:

I measured an old camshaft and it is 0.240" so take off 0.010" clearance = 0.230 x 1.45 = 333 not the the 0.350" as in all the charts

But I will still have 0.050" more lift so I suppose it is all relative?

 

So I gave up as the post man delivered a new Woodruff key, so I thought I would fit the front engine plate properly.

But when I came to fit it it is wrong its 0.200" wide and should be 0.187 and supplier said they are all the same in his stock!!!!(I wish I could find the old one)

So I decide to fit the rear seal and engine plate but I noticed and arrow on the plate and wondered why Triumph stamped it there?

 

Nasty key!

Arrow is a TDC mark, there would have been a matching one on the flywheel.

re lift, sorry Roger but you keep taking the clearance off the lift, it has to come off after applying the ratio. i.e. (0.240 x 1.45) - 0.010 = 0.338 (still not 0.350 though!)to get that you have to use the fictitious 1.5:1 rocker ratio  0.240 x 1.5 - 0.010 = 0.350  (old myths will last almost forever it appears when cast in stone) 

Alan

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19 hours ago, oldtuckunder said:

Nasty key!

Arrow is a TDC mark, there would have been a matching one on the flywheel.

re lift, sorry Roger but you keep taking the clearance off the lift, it has to come off after applying the ratio. i.e. (0.240 x 1.45) - 0.010 = 0.338 (still not 0.350 though!)to get that you have to use the fictitious 1.5:1 rocker ratio  0.240 x 1.5 - 0.010 = 0.350  (old myths will last almost forever it appears when cast in stone) 

Alan

Hello Alan

                   I still think the clearance comes off first because there is no valve or rocker movement until the clearance is taken up so there is no rocker ratio multiplier on that bit!

Plus when I did a bit of measuring on No1 and No2 it came out as I expected ie 0.278 cam lift - 0.014" = 0.264" x 1.45 = 0.3825 which is what I recorded?

Plus the Newman camshaft has the the clearance built in ie 0.270" + 0.014/16" (0.284")approx were as the Triumph camshaft measures 0.240" lift so it is only going to give 0.230" lift when the 0.010" clearance is taken up?

Tomorrow I am going to put the camshafts in the lathe between centers and measure lifts accurately as I can not fit it properly until I had a crankshaft woodruff key just for my own satisfaction .

The next thought is if there is a difference in cam lift could I use different clearances so all valves open the same?(probably pointless as we are talking a few thou!)

Still food for thought?

Roger

ps still hoping someone has a bag full of good woodruff keys or I will just have to make one? I am sure I have got some good steel about the place and the bad one was hardened! were the triumph ones? in all my days in engineering I always thought they were tough not hard? and in machines often designed to break before major damage occurred! but perhaps not in engines plus mine will be doing less work than a TR6.

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9 minutes ago, rogerguzzi said:

Hello Alan

                   I still think the clearance comes off first because there is no valve or rocker movement until the clearance is taken up so there is no rocker ratio multiplier on that bit!

 

It can't be!   If we take a fictitious 1.5:1 rocker arm and you have a clearance measured between the tip of the rocker and the valve stem of 0.015, then if you push the  tip of the rocker down to touch the valve stem, how much has the push rod side of the rocker arm moved up?   0.010 !  So you can't take the clearance of the cam lift before multiplying by the rocker ratio to calculate real valve lift, it has to be subtracted afterwards.

Alan 

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While I was out in the garage this pm, I got out some old rocker assemblies and measured one.    Only with a Vernier gauge, so not high precision, but anyway.

Sure enough, I found that the distance from the centre of the ball that the push rod presses on to the centre of the rocker shaft is 15.8mm and from there to the centre of the pad that bears on the valve stem is 24.7mm.   So the ratio is 1:1.56, which agrees with the 1:1.55 quoted by Roger.  Not to check up on you, Roger, but to add veracity to the next bit.

The rocker rotates on the centre of the rocker shaft, which is B in the diagram above, while C is the centre of the adjustment bolt.     When the rocker rotates, it moves to the line AB.    Now the distance between B and the adjuster is DB.    If AD is a typical cam lift, 250 thou or 6.35mm, DB can be calculated by Pythagoras.

AB^2 = AD^2 + DB^2

So DB^2 = AB^2 -AD^2

And DB = SQR (AB^2 -AD^2)

Putting in values:   DB = SQR (15.8^2 – 6.35^2) = 14.47.

 

Meanwhile, the valve stem has not moved, the pad on the rocker has wiped across it, and is the same distance from the rocker shaft.  The ratio is now 24.7/14.47 or 1:1.7

So the rocker ratio depends on cam lift, and increases as the cam rises.

Rocker movement.png

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As you have your calculator head on John :biggrin: can you add two extra factors in?  1) The tip of the rocker is curved so as it wipes the valve stem the ratio reduces 2) The effective height of the rod when at C and the effective height of the rod when at A isn't the same as the rod at A is at an angle, and two (from what I read) the point of contact between the the cup in the rod and the ball on the adjuster also moves in a small arc also affecting the effective length of the rod.

When I have my engine running! and have an hour or so I'm also going to measure a few rockers, as again (what what I have read) you cant just take the measurement from the ball of the adjuster to centre of the rocker, and the centre of the rocker to the tip, what you have to do is draw a line that goes from the centre of the ball through the centre of the rocker and out the other side, if the tip of the rocker doesn't sit on that line, then the ratio isn't a straight calculation, I haven't measured a triumph rocker to see yet.

However as an observation if one of the cam manufacturers knew that at towards full lift  the standard Triumph rockers were giving 1:1.7 lift I think they would be claiming much better valve lift figures than they do.

Actually as Roger is playing at the moment we ought to get him to adjust a rocker to zero clearance and put a dial gauge on the rocker tip and a dial gauge on the adjuster tip, and see what the results are?

Alan

 

 

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Hello All

               I have measured the cam lift in the lathe between centres and the results are 1 to 8   .286 .281 .286 .286 .283 .282 .285 .281  (I measured an old Triumph one and it was 0.240" and all were very close)

So the valve clearance is is add to the cam to give .270 lift  

I recon with the 1.45 rocker I will get between .392" and .402" approx

I do not suppose 0.010" will make much difference! ( I did think they would be closer than that?)

The next question is why do Newman call for 0.014" & 0.016" clearance? (Triumph is 0.010")opening characteristics, quietening ramps? 

With some clever calculations I could adjust the clearances so all valves open the same amount! (probably not worth the effort!)

I have made a nice Woodruff key that is a good fit and it is amazing how little there is of it in the chain sprocket!

Roger

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Will be interesting to measure valve lift with zero clearance  as this will allow calculation of the actual effective rocker ratio.

would have expected more even lift numbers on a new cam.  Grinding is supposed to be one of the highest precision processes!

Nick

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On 11/03/2018 at 7:19 PM, oldtuckunder said:

As you have your calculator head on John :biggrin: can you add two extra factors in?  1) The tip of the rocker is curved so as it wipes the valve stem the ratio reduces 2) The effective height of the rod when at C and the effective height of the rod when at A isn't the same as the rod at A is at an angle, and two (from what I read) the point of contact between the the cup in the rod and the ball on the adjuster also moves in a small arc also affecting the effective length of the rod.

Alan

Again, looking at the rocker, it seems that a line joining the tip and the centre of the shaft, passes above the ball that takes the push rod.   Then the centre of the ball is  slightly nearer the shaft centre at rest than it will be when the cam lifts the rod and the valve.    The ball has a diameter of 8mm, so the radius is 4mm, similar to the 6mm of lift, so the reduced distance is approximately the same as the movement nearer the centre that I calculated, so the ratio may start at more than 1:1.55 and approach that at the end of lift.

On your points, Alan

1/ Yes, I think I misled myself.   The contact point of tip in stem will be closer to the rocker shaft at max.lift, so the change in ratio will not be so great.

2/ Yes, the rod will be at a small angle, reducing it's height somewhat.  Need to measure a rod and calculte that, but given that a rod is about 200mm long and the angle will be tiny, that reduction will not be great.   But I don't think the effective rod length is affected by movement of the ball and cup, which will be concnetric abouit the ball's centre.

John

Edited by JohnD

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Really interesting thread !

my 1980’s engine notes state clearances of 24th cold, which seems huge to me!

i’m unsure what the cam is, there are ‘777’ references in the notes

Why would so large a clearance be required/recommended, surely this just reduces the valve lift?

steve

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1 hour ago, SDerbyshire said:

Why would so large a clearance be required/recommended, surely this just reduces the valve lift?

 

For the real reason you'd have to ask the cam designer, but as we know that clearances are nothing to do with heat expansion (or very very little using standard material rods'n'rockers) some of the effects of a larger clearance are to help prevent trashing a cam where the initial opening/closing ramps are too sharp, i.e the cam has rotated a few more/less degrees before it "thumps!" or "drops!" the follower, also that few extra degrees at each end also has an effect of reducing the total duration of the cam, and also the effective overlap of the valves, so tongue in cheek one could possibly posit that upon finding one had designed a cam with too much lift, too much duration, too much overlap, or was eating followers or lobes, or any combination of those, that increasing the clearance from 0.010 to 0.024  was a quick and cheap solution, or an elegant design solution, depending on your view point!

Alan 

One other valid reason for doing so (if the rocker ratio does alter during rotation)  could be to do with moving the valve lift characteristic at a specific point during the lift, as it appears the higher the acceleration of the valve between 50-75% of lift the more beneficial it is, a wider clearance might just pull a few more degrees of cam rotation into or out off this period.  Could be that someone by trial and error (or as engineers call it scientific experimentation) discovered that 0.024 worked well!  

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10 hours ago, SDerbyshire said:

my 1980’s engine notes state clearances of 24th cold, which seems huge to me!

i’m unsure what the cam is, there are ‘777’ references in the notes

Why would so large a clearance be required/recommended, surely this just reduces the valve lift?

 

Found a couple of notes on the Tilden Triumph Cams page which I have just found http://www.tildentechnologies.com/Cams/TriumphCams.html  and a bit more reading to do there yet.

"We selected a fast road cam from a reputable supplier, but without knowing the duration at 0.050. When we degreed the cam, we found that the seat duration was 8 degrees more than stated, the duration at 0.040 net was about 251 degrees.  The lift was greater than specified.  This was more of a race cam than a fast road cam. I should have returned the cam because it did not meet the specs.  Instead, I installed the cam using a larger valve lash to achieve the specified duration."

  Interesting the note about altering lash "Clearance to you and me" to alter the duration.

Also a note on how clearance affect lift (haven't checked what the formula does yet!) and that they assume that exhaust lash is .002 greater on exhaust than inlet, which out of interest if your exhaust clearance was .024 that would make the inlet .022 which seems to be the inlet clearance that Revington specify for their cams, which are I believe Kent profiles and the clearance they recommend,  and I also believe that Kent also inherited a bunch of the Triumph Tune profiles, and believe it or not there was a TT 777 cam.  The .022 Inlet clearance on all these cams mark's them out uniquely as nobody else uses clearances anywhere near as big! So it might be a good indicator of your cams origin.

Intake lash listed, exhaust is the same or 0.002 greater
The difference between net lift and gross lift = Lash/(1.48) + 0.003

Actually just found this note on TRR thread

Hi I have a similar cam in my 67 4A. They were made by Kent for Racetorations & 777 istheir no. which is why Kent didn't recognise it. The valve clearances should be as Badfrog suggested - 22 & 25 thou. Hope this helps
 

Which seems to probably identify your cam Steve

 

Alan

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Hello Alan

                  I had read that site before and still know nothing!

I have reached the stage now I am just going to fit the cam and see what it is like!(I think I managed to get the timing right today?)well + 2degs

I have the advantage I think running fuel injection I can adjust running better(fuel and ignition!)

Plus it is driving me mad!

Plus found out today I had bolted the toothed wheel on in the wrong place!!!!!!!!!!!!!!!!!!!!!!!!(still I do not think the missing tooth will make much difference to the balance overall?

I think I may use the small valve head as it is new and has seat inserts (and I have ported it) and the few BHP I lose will not matter on a road engine?

Must finish the sump baffle?

Roger

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2 hours ago, oldtuckunder said:

Actually just found this note on TRR thread

Hi I have a similar cam in my 67 4A. They were made by Kent for Racetorations & 777 istheir no. which is why Kent didn't recognise it. The valve clearances should be as Badfrog suggested - 22 & 25 thou. Hope this helps
 

Which seems to probably identify your cam Steve

 

Alan

Thanks Alan!

one day the engine will need to com apart and all will be revealed, notes also refer to forged pistons, ‘con rods as supplied’ and other mysteries.....

since the motor runs superbly i’m leaving it well alone until it doesnt :-)

steve

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30 minutes ago, SDerbyshire said:

since the motor runs superbly i’m leaving it well alone until it doesnt :-)

 

From one who in the past? has been tempted to gild the lilly, I'd say keep that thought!

Alan

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