Hi, Having looked through other forum posts I am still unsure if I have got the cam timing marks correct. engine is a 1951 6T without ramp cams. The cranksaft is set at TDC in the image attached, have |I got it right ??. Many thanks in advance Alan
At first I didn't think so, but after looking at the manual ( No. 17 ) and your pic several times...I would say it is. Are these single key camwheels or three way key and are these the camwheels that came with your engine ?
I have also checked with my Clymer manual, printed in July 1951 but the pic leaves a little to be desired fro clarity concerning aligning the timing wheel marks.
The 1945-55 manual shows timing marks for ramp cam 5t, 6T and T100; then for TR5 and T110 with "fast road" cam.
It does not specify dot or dash for non-ramp touring cam.
A retarded (by one tooth) inlet cam gives you very stodgy low to mid RPM performance; too advanced makes the inlet valve hit the piston.
You can check for safe valve to piston clearance by adjusting the inlet valve clearances to minus one whole turn of the adjuster and turning the engine over slowly. I mean close the gap to zero with the follower on the back of the cam and give the adjuster another whole turn in the closing direction, thus holding the valve about 30 thou open.
Pete's advice on the other forum is more precise and worth doing, too.
The engine was 'reconditioned' in 1963, my dad thinks it was just a rebore, pistons and valves but he cannot be sure the cams were not changed. I think the best way is for me to check valve timing with dial gauge and degree disc and see where the valves are opening and closing. The head is off and I will be measuring lift at the cam follower where it comes out of the tappet block.
I have asked Mr Pete for some advice on the other forum but any further thoughts on how to go about do this bearing in mind the timing figures I have are for 20 thou valve lift and I will be measuring straight from the cam follower.
Regarding measuring at 20 thou lift at the cam follower/tappet block I have a question: are the rockers ratio 1:1, i.e when the pushrod lifts the rocker 20 thou does the 'tappet end /lash end move down 20 thou. If it does not then trying to time at 20 thou lift at the cam follwer will give false readings on degree disc ?
Thanks for the help up to now, really appreciated.
Having checked the inlet cam something is clearly not right with the cam, or me
The base circle of the cam seems slightly uneven with my sensitive dial gauge so I have set the zero / base position of the cam to be checked by setting the other tappet at full lift.
at 20 thou lift I am getting the following:
opens 20 deg BTDC closes 30 deg ABDC
Right Cyl: opens 20 deg BTDC closes 35 deg ABDC
I found a photo I took whilst dismantling and re the cam wheel positions they were as shown in photo OTHER THAN the inlet cam was timed with the long dash between the dots NOT the short dash as in the photo. The bike has been timed like this since 1963 and was used and ran Ok for some 15 years before being taken off the road. The timings above are with the long dash aligned.
With the short dash timing are: Inlet (left and right) opens 5 deg BTDC closes 45 ABDC
And finally: full lift .225 left, .246 right
Mr Pete: re difference in lift:
right cylinder : lift at tdc 62 thou, at BDC 98 thou, therefore 36 thou difference
left cylinder: at tdc 33 thou lift, at BDC 139 thou, therefore 106 thou difference.
So is it a worn cam or am I doing something wrong:
I agree taking the cams out would probably allow me to assess their condition / what they are but, this means buying another expensive tool !! Was hoping a timing exercise would solve it (should have known better)
Anyway.... checking timing with NO tappet clearance gives:
So......given that full lift is down between 0.020 and 0.035 from the lift of a ramp cam (0.270) is it possible that by measuring with no clearance the 0.020 'setting' clearance is accounted for by the wear... i.e measuring with no clearance on worn cam same as measuring with 0.02 clearance on unworn cam, Or am I just talking rubbish ????
If they were non ramp cams, wear would be 0.040 to 0.070 so well ****ered.
Would like to bottom this 'cam timing' exercise for interest sake in addition to future reference for me and possible others.
So any thoughts ?
Last edited by Cloggy; 02/01/145:50 pm. Reason: correct some values
Runs at 2 & 4 clearance . In & Ex . Though trying 10 wont hurt .
GLAREING at the Cam should see if the lobes have evaporated - in part . They score / scour , across the top of the lobe .
IF theyre all shiney & polished , no dull flat bit - theyre fine . Overreving or Wrong Lifters can WIPE the TOP of the LOBE , the hard edge of the lifter shaveing it . Solution ' R ' 3/4 radius lifters .
As performed, measuring the .020" tappet lift is done directly off the top of the lifter.
The Triumph factory cam timing figures are given for tappet lift, not valve lift.
The push rods and rocker boxes are not on the engine and are not part of the exercise.
Looking at Triumph manual 17 page 64 it describes method of cam timing. It says the 20 thou clearance is at the valve with head and rockers fitted. Mr Pete has provided info elsewhere that rocker ratio is about 1.125:1 so does that not alter the clearance used if measuring from cam follower and therefore the degree values obtained for valve opening/ closing ?
OK, dusted off the old No. 17 manual, and yes it is as you describe.
That said I have long abandoned using opening and closing figures to time camshafts at low lift figures (@.020" - .050"). I have more faith in the method often used in the UK where measurements are made for lift @tdc, but I have abandoned that method except for the occasional Trident or T140. What I done is adopted the "lobe center" method where one does not need to know opening or closing numbers to time the camshafts.
To quote Brian Jones: "While when we went to Taiwan to have camshafts made for the Harris Bonneville they gave us camshafts that were exactly as the drawing specified. This was something we were unable to do in Meriden. To bad they didn't have the metallurgy as the cams were prone to failure. We finally went to Italy for the cam blanks and had them ground in the UK."
The actual measured side-to-side (left intake vs right intake) intake and closing figures on factory Triumph camshafts are rarely the same and to the drawing. After market performance cams are rarely better. The keyways in the camshaft and timing wheels are rarely cut exactly to the drawing. The relationship between the keyway (keyways - three keyway wheels) and gear teeth, although pretty good considering production techniques available at the time, are not the same from wheel to wheel (a feature which is handy when trying to move the lobe center one or two degrees).
So if you are looking to get exactly the figures listed in the manual don't be surprised if you don't. As far as the difference you will get with the dial indicator measurement at the lifter instead of the top of the valve spring collar the lobe center of the camshaft will not change. The 1.1 to 1 rocker arm ratio effects valve lift, not cam timing. Yes the timing figures you get at the 0.020" tappet will be different, but not in significantly. It might be a degree less, but so to would the closing figure.
I have been using "lobe center" method for as long as I can remember. While initial lobe center figures can be taken from the listed opening and closing figures, the final measurements are taken 0.100" to 0.150" down from either side of full cam lift. The point in the middle between these two points is the cam's lobe center. And as Leo Goff is fond of saying, "Any cam can be timed @ 105° lobe center and perform pretty well." Normal lobe centers are typically between 99° and 115° depending on what you expect the cam to do.
Using the figures you listed above inlet (long dash aligned) opens 43 BTDC (spec 26.5) closes 61 ABDC (spec 69.5)
So take these opening and closing figures above and calculate Lobe Center: 43° + 180° + 61° = 284°/2 = 142 - 43 = 99° Lobe Center (Bonneville with E3134 cams Lobe Center is 100.5°)
So take these opening and closing figures above and calculate Lobe Center: 61° + 180° + 43° = 284°/2 = 142° - 43° = 99° Lobe Center (Bonneville with E3134 cams Lobe Center is 100.5°)
Lobe Center explained: (as best as I can) You add the degrees at camshaft opening (before TDC for intake or BDC for exhaust) to the distance the cam rotates between Top Dead Center and Bottom Dead Center (Bottom Dead Center to Top Dead Center for exhaust) or 180° to the degrees the cam rotates until it closes. So we get 43° + 180° + 61° = 284°. We want the mid-point so we divide this by 2. 284/2 = 142°. So the cam is opening at 42° Before Top Dead Center and to calculate how much farther it will rotate past TDC to reach Lobe Center we need to deduct the 42°. Thus we get 142° - 43° or an Intake Lobe Center of 99° After Top Dead Center.
So a Bonneville Intake cam, with its 100.5° Lobe Center, would reach full lift some 10 degrees sooner than a 6T with a 111° Lobe Center.
Many thanks, got the idea of lobe center now and it makes sense to use that..... Once the lobe center is right the opening and closing points take care of themselves and are down to the cam profile.
Still think, as has been said, that my cams are well worn because of the reduced full lift and supported in that the as the timings given, that you used to explain lobe center, are with no tappet clearance.
So..cam lobe centre on my inlet cam is 99 or 116 depending on which timing mark I use. Should be 111 (I got 108 using the triumph standard cam figures to do the calculation)so I am about in the middle. So which is best 99 or 116 ?
Finally in your calculation of the exhaust you deduct the closing value (43) but on the inlets you deduct the opening value ? Is this right, that bit confuses me a bit.
...I tried to understand all these numbers but looks almost impossible to me right now (I want to clarify that Im not a "brute" guy. I like to study, I study music, languages, etc)
My experience is that I never measured any of these numbers due to the worn or too old the piece itself is. I only put the gears on the factory marks...is that not enough? then checked the valve clearance then timed the magneto. My bike is old but is a 1 kick bike. I think this is a distinctive Triumph thing: 1 kick; if a Triumph does not start on 1 kick (after you flooded the carb) something is wrong.
15 - 20 years later Im building a newer one and I used again the factory marks...so Im very intrigued but all those numbers. Also I checked other thread about the T140 timing and the numbers are pretty different than what the factory workshop manual says... Here s a photo showing the timing marks for the T140
Reverb: The truth be known, for a given set of factory cams I too just use the factory timing marks on a rebuild. It is when I have a situation where I have a set of cams that I am not familiar with, and have no timing information, that understanding lobe center timing comes in handy. If you are like most people who just want to assemble the motor and go for a ride, don't read any further! But for many reasons including that these bikes have had many owners, and many uses, over the past 50 years, and you are not sure you have a set of factory cams continue reading.
I always use Lobe Center timing when ever I am timing in a set of "performance" camshafts, or ones I have no information on. I do this because it is a more accurate method, and knowing the actual Lobe Center, when I do stumble across some real horsepower, allows me to retime the cams exactly as they were when I took the engine apart. A key to performance is knowing, and documenting, what you have done so you can repeat the success you had over, and over, again.
Here's the point with performance camshafts, in the words of Eddie Mulder, "The cam timing figures I use for the power curve I am looking for is never found on the cam timing sheet that comes with the cams!" (I am paraphrasing his remarks) The cam timing for a given set of cams, for one type of racing or rider style, might be totally different from another. The information on the sheet that comes with the cams is a point to start, but if you are serious about finding horse power that you can use, by no means will you find your use full Lobe Center on a sheet of paper. But in the end you are going to end up somewhere between a 98-99 and 115° 118° Lobe Centers, give or take.
There is a lot written about advancing and retarding cams, and it is easy to find on the net. And remember what is good for one type of racing, track conditions or rider style is not always going to suit your expectations. Most articles on cam timing will lead you to understand what will happen you advance or retard a camshaft, but in the end it is only you that can determine if the power curve you get will be use full. You could easily have one preferred Lobe Center for a set of cams for a short track like New Hampshire Speedway, with all of its tight corners, and something different on the same bike for Daytona.
Remember the docile, tourer 6T @ 111° Intake Lobe Center and the more perky, but less docile, Bonneville @ 100.5° Intake Lobe Center.
Now when you time in a set of cams using the Lobe Center method you take your measurements with a dial indicator (typically from the tappet) @ .100" to .150" either side of lobe's maximum lift. You then take the reading off the degree wheel at these points and the Lobe Center is half way in between the two.
Degree wheels designed for timing cams will have the Intake and Exhaust Lobe Center areas marked. This is extremely helpful when you are just starting out degreeing cams using the Lobe Center method. If you are serious you need a degree wheel that is at least 12" in diameter, while NASCAR types will use one 24" or larger. When you are looking for real HP a half degree matters, and only a large diameter degree wheel will give you that accuracy. This is a 12" one that I have been using for years. It is the same one we used in the cam timing article in Vintage Bike a few years back.