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#409275 - 12/18/11 6:15 pm Cam Timing  
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db133 Offline
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Hi

I have the head & rocker box's off a pre unit bits and bobs 5t . The cam pinnions have only one keyway. I have taken a picture of the dots. I put some tape where the dots a very small.

I have a degree wheel and a couple of dial gauges. I want to know how these cams have been set up before its taken apart.

Will some one be kind enough to inform me of the correct method to find out how these two cams have been set up ?

I do not want to make a mistake with the information. I can put it back as it is but how do I know that is right ? I wont know what cams are in there until its apart. Then If I have made f**k up all's lost if that makes any sense ?

In any event kind regards.



Last edited by db133; 12/18/11 6:16 pm.
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#409309 - 12/18/11 9:08 pm Re: Cam Timing [Re: db133]  
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You could just move the idler wheel one tooth counter-clockwise,without moving the crank or cams.The timing marks on the idler would line up with the crank,the exhaust camwheel and the lower mark on the intake camwheel.
If you turned the engine enough rotations,this would eventually happen without dis-engaging the idler.

Is it the best cam timing to use?Who knows?Set the dial gauge up on the pushrods and get some readings on the degree wheel at 0.010" lift,0.020" lift and 0.100" lift.Also measure the maximum lift.

That should tell you how good it is.

#409327 - 12/18/11 11:23 pm Re: Cam Timing [Re: db133]  
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Pete R is right. The marks will eventually line up with enough turns of the crank. This is called the "hunting tooth principle". The marks only line up every 94 revolutions (I think it was).

#409419 - 12/19/11 4:09 pm Re: Cam Timing [Re: db133]  
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db133 Offline
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Ref:
Is it the best cam timing to use? Who knows? Set the dial gauge up on the pushrods and get some readings on the degree wheel at 0.010" lift,0.020" lift and 0.100" lift.Also measure the maximum lift.

*Is the degree wheel set to 0 at the TDC on the compression stroke on each cylinder and all readings taken from there ?

Reading through 'The book of the Triumph' page 95 has the 5t 37/8
at Inlet opens BTC 21 degrees
" closes ABT 75 "
Exhaust opens BBC 75 "
Exhaust closes ATC 21 "

5t/T100 1939 :

Inlet opens BTC 26.5 degrees
" closes ABT 69.5 "
Exhaust opens BBC 61 "
Exhaust closes ATC 35 "

*I dont understand the term's BTC, ABT, BBC, ATC.

*Sorry if its a stupid question but I'm a bit Dyslexic and the other bit is daft !

Kind regards.

#409442 - 12/19/11 6:44 pm Re: Cam Timing [Re: db133]  
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0 the degree wheel at top dead center

BTC = before top center
ATC = after top center
BBC = before bottom center
ABT ... maybe that should be ABC = after bottom center

It would be worth checking the cam timing, especially for competition bikes.

#409491 - 12/19/11 10:47 pm Re: Cam Timing [Re: db133]  
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Set the wheel at zero TDC,when the piston is fully up (top dead centre).Check it by moving the piston to equal distances before and after TDC,say 0.500" before (coming up) and 0.500" after TDC (going down).The degree readings should be equal angles from TDC,if the wheel is set right.
180 degrees before or after TDC IS BDC (bottom dead centre).

The later exhaust timing (61/35)sounds good enough.A couple of degrees either way (advanced or retarded) would still be OK.

I think there's still room for improvement on the intake timing.
33/63 timing or even 38/58,would probably work better.You'd need to check piston-to-valve clearance,but it should be OK.

You're limited by only having one keyway in the camwheels.One tooth (14.4 degrees) is a big change in timing.With a 3-keyway wheel,you could adjust in 4.8 degree increments (a different timing mark would be necessary,if you don't use the "standard" keyway).

#409542 - 12/20/11 11:02 am Re: Cam Timing [Re: db133]  
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Thanks for your input. started with left cylinder (as sitting on bike) or drive side. set degree wheel to 0 at TDC ignition stroke (points on bottom cam).

Set my dial gauge up on inlet tappet follower for that cylinder at 0.


Last edited by db133; 12/24/11 9:59 pm.
#409547 - 12/20/11 12:21 pm Re: Cam Timing [Re: db133]  
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We'll call that 247 degrees 113 degrees BTDC.The 157 degrees would be 23 degrees BBDC.The angle of max. lift isn't so important;how much was the lift?I think 0.295" is standard.

You've got 1/2 the figures you need.Get the 0.010",0.020",and 0.100" lift figures on the closing flank of the cams (when the cam-follower is moving back down).

I notice it takes 74 degrees to get from zero up to 0.020" lift.They must be ramp cams.
So far,so good.It doesn't look terrible.Come back with the rest of the figures,and we'll know the full story.

#409583 - 12/20/11 6:20 pm Re: Cam Timing [Re: db133]  
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If you are putting it back up as a 5T, then I believe you'd want to use the retarded intake mark used for 6T. This will give you smoother idle and much higher fuel mileage. If you don't end up liking it, then it's a very simple matter and ~10 screws to move the intake came 1 tooth. Takes maybe 15 minutes on a running 5T.

The guys are right, with zero valve spring pressure you can simply slide the intermediate wheel out and rotate it one tooth to get the existing marks to line up. Good of you to remove the camwheel nuts to see the keys. Very clean.

The true reason to ID the cams is to know the correct valve lash settings.

bigt


Don't hide 'em, Ride 'em !!

RF Whatley
Cornelia, GA

"Shop Boy" at Rodi British Bikes
#409713 - 12/21/11 3:10 pm Re: Cam Timing [Re: db133]  
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LHS/Primary Revised 24.12.11
Inlet

Start = 73 ABC

0.010 = 57 BTC
0.020 = 28 BTC
0.100 = 17 ATC
Max = 78 BBC
0.100 = 17 ABC
0.020 = 67 ABC
0.010 = 76 BTC
Close = BTC 15


Exhaust
Start = 40 ATC

0.010 = 87 ATC
0.020 = 65 BBC
0.100 = 21 BBC
MAX = 72 ABC
0.100 = 16 BTC
0.020 = 32 ATC
0.010 = 71 ATC
Closed = 48 BBC


RHS/Timing

Inlet
Start = 80 ABC
0.010 = 52 BTC
0.020 = 26 BTC
0.100 = 16 ATC
MAX = 74 BBC
0.100 = 18 ABC
0.020 = 61 ABC
0.010 = 88 ABC
Closed = 25 ATC


EX
Start = 42 ATC
0.010 = 88 ATC
0.020 = 65 BBC
0.100 = 20 BBC
Max = 72 ABC
0.100 = 17 BTC
0.020 = 34 ATC
0.010 = 70 ATC
Closed = 57 BBC




Last edited by db133; 12/26/11 10:42 am.
#409718 - 12/21/11 3:24 pm Re: Cam Timing [Re: db133]  
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Found this.

Valve Lash
What is Valve Lash?

Valve Lash - Lash or Valve Clearance is the gap between the Rocker Arms and the valve tappet. This clearance must be tightly controlled. If it is too little, the valves may not seat properly. If it is too much, you create valve train noise, and excess load on the valves and valve train components.

Valve lash basically cuts off the lower portion of the cam profile. This lower section is where the cam profile is designed to gently open and close the valve. If you have too much valve lash, you eliminate the more "gentle" sections and are basically "slamming" the valve open and closed.

Too Much Valve LashBecause of manufacturing tolerances, engine wear, and because different parts of the valve train and engine "grow" as the engine heats up, this clearance can change and must be set correctly. Camshafts are ground assuming a certain amount of valve lash. If you change it, you risk changing the performance and durability of what the cam grinder designed into their lobes.
............................................

I think we call it 'setting the tappets'.

I notice in 'The Book of the triumph' 'all valve timings given should be checked with nil valve clearances. This is important'. Although I read elsewhere set to 20 thou to check ? More questions......






Last edited by db133; 12/21/11 3:53 pm.
#409724 - 12/21/11 3:46 pm Re: Cam Timing [Re: db133]  
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Yes Sir,

What you said db133. A couple thou difference, (can't figure the percentage). I mean on stock cams for 71 T120, will also effect how and where the "power band" occurs.

Some people, John has noted before, that the idea started in the Western US, say to run a few thou greater than the manual suggests. My experience is that I like the way the engine performs at the manual recommended specs. That is running in the hills of old New England, with all the atmospherics customary to that local. And trying to keep the RPM's at least above 3500.

Last edited by btour; 12/21/11 3:48 pm.

Bob, Lifetime bike: '71 T120R, bought in '71 at Ken Heanes, England.
#409725 - 12/21/11 3:57 pm Re: Cam Timing [Re: db133]  
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There is usually
a few thousandths latitude between tight and loose valve lash. An experienced mechanic can determine this range by careful experimentation. The clearance can be changed within the range to tailor the engine performance to a particular application.
In general: More clearance will sharpen up the low and mid range and reduce top end. Please start by installing your cam with the
valve lash settings listed on the timing card supplied with each Megacycle Cam. Adjust valve lash according to the application.
I run the intakes a little loose to close the valve earlier and shorten the overlap.


1968 T120R
1972 T120RV
Any advice given is without a warranty expressed or implied.
#409728 - 12/21/11 4:06 pm Re: Cam Timing [Re: desco]  
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Originally Posted By: desco

I run the intakes a little loose to close the valve earlier and shorten the overlap.


des -

Just curious: how much, exactly, is "a little loose"?

TIA,

Steve


'77 T140J
"Vintage Bike". What's in your garage?

"The paying customer is always right."

Fitting round pegs into square holes since 1961...
#409729 - 12/21/11 4:17 pm Re: Cam Timing [Re: db133]  
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I am following this topic with interest. I too am learning about cam timing.

db133: I see a huge difference between RHS and LHS exhaust opening numbers. Typo or check your measurements ??

#409732 - 12/21/11 4:31 pm Re: Cam Timing [Re: rstar45]  
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Just curious: how much, exactly, is "a little loose"?

JP
Megacycle recommends .010 for my cams. At high speed,over 80mph, I was getting as much gas blowing back out the carbs as was going in. Changing the intakes to .013 stopped that and vastly improved low speed performance.
Just re-read this saw my mistake, .013 not .007. Why I'm a carpenter and not a mechanic.

Last edited by desco; 12/21/11 5:16 pm.

1968 T120R
1972 T120RV
Any advice given is without a warranty expressed or implied.
#409819 - 12/22/11 2:30 am Re: Cam Timing [Re: db133]  
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I was confused at first,then I figured that the closing readings were done turning the engine bacward.So,ABC figures were read as "BBC".Backlash in the gears will have a small effect,if you turn the engine backward.It won't be much,about one degree.I think this is how the intake figures came out,allowing for that.
TIMING SIDE INTAKE
@ zero LIFT: opens 110 BTDC closes ?
@ 0.010" LIFT: opens 60 BTDC closes 53 ABDC
@ 0.020" LIFT: opens 31 BTDC closes 46 ABDC
@ 0.100" LIFT: opens 15 ATDC closes 11 ABDC

PRIMARY SIDE INTAKE
@ zero LIFT: opens 105 BTDC closes ?
@ 0.010" LIFT: opens 62 BTDC closes 50 ABDC
@ 0.020" LIFT: opens 31 BTDC closes 43 ABDC
@ 0.100" LIFT: opens 15 ATDC closes 9 ABDC

The 0.010",0.020" figures are misleading at the closing points.
The INTAKE cam lobe centre is 102.5 degrees ATDC,if the 0.100" figures are right.That would be good timing.
Max lift at 105-108 degrees.That doesn't exactly agree with 102.5 degree centre,but it's close.A 0.003" error,or combination of errors,on the cam and tappet could cause that difference.
If you get about 0.055" lift at TDC,about 0.125" lift at BDC,leave it alone.Eyeball or steel rule measurement will do.

The exhaust figure don't look right,and one side doesn't agree with the other side.
EXHAUST
@ zero LIFT: 54 BBC/?ATC (T-side) 140BBC/?ATC (P-side)
@ 0.010" LIFT: 47 / 87 . . . . . . . . . .88 / 87
@ 0.020" LIFT: 41 / 79 . . . . . . . . . .66 /79
@ 0.100" LIFT: 12 / 42 . . . . . . . . . .23 / 42

I think you need to check the exhaust again.If any of the figures are right,it's a very hot cam but incorrectly timed.

To avoid much confusion,first check the lift at TDC,BDC.You should have about 0.080" more lift at BDC.Adjust the cam timing,to the nearest tooth,to get this.Disengage the idler wheel and adjust the exhaust cam,so your close to that.

Then take readings again,and table them as above.It's much easier to read,that way.

#409844 - 12/22/11 8:44 am Re: Cam Timing [Re: db133]  
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REF:
"I was confused at first,then I figured that the closing readings were done turning the engine bacward."... ....................

Sorry to inform the above is incorrect.

Page 29 Haynes confirms correct direction.



I will go back over it all.

Last edited by db133; 12/22/11 11:47 am.
#409845 - 12/22/11 9:11 am Re: Cam Timing [Re: db133]  
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Quote:
I will go back over it all but can someone confirm which way to turn the engine ?


The engine rotates forwards, clockwise when viewed from the timing side.

You should always check your valve and ignition timing by rotating the engine in this direction since it will minimise any errors due to backlash in the timing pinions.


1952 Triumph T100 in a BSA A7 Frame
#409852 - 12/22/11 11:39 am Re: Cam Timing [Re: Mattsta]  
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db133 Offline
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The engine rotates forwards, clockwise when viewed from the timing side.

You should always check your valve and ignition timing by rotating the engine in this direction since it will minimise any errors due to backlash in the timing pinions.

Exactly.

Please find revised figures as at 24.12.11
LHS/Primary
Inlet

Start = 73 ABC

0.010 = 57 BTC
0.020 = 28 BTC
0.100 = 17 ATC
Max = 78 BBC
0.100 = 17 ABC
0.020 = 67 ABC
0.010 = 76 BTC
Close = BTC 15


Exhaust
Start = 40 ATC

0.010 = 87 ATC
0.020 = 65 BBC
0.100 = 21 BBC
MAX = 72 ABC
0.100 = 16 BTC
0.020 = 32 ATC
0.010 = 71 ATC
Closed = 48 BBC


RHS/Timing

Inlet
Start = 80 ABC
0.010 = 52 BTC
0.020 = 26 BTC
0.100 = 16 ATC
MAX = 74 BBC
0.100 = 18 ABC
0.020 = 61 ABC
0.010 = 88 ABC
Closed = 25 ATC


EX
Start = 42 ATC
0.010 = 88 ATC
0.020 = 65 BBC
0.100 = 20 BBC
Max = 72 ABC
0.100 = 17 BTC
0.020 = 34 ATC
0.010 = 70 ATC
Closed = 57 BBC




Last edited by db133; 12/26/11 10:52 am.
#409855 - 12/22/11 1:56 pm Re: Cam Timing [Re: db133]  
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The points of maximum lift seem to be in about the right place: INTAKE : 105-106 degrees ATDC
EXHAUST :103-105 degrees BTDC
How much is the maximum lift?

The trouble is the intake closing points are all listed as BEFORE BDC.Surely the piston goes all the way to BDC,and then starts coming up from bottom before the valve is closing?If it still has 0.100" lift at 7 degrees BBDC,it can't have 0.010" lift at 50 degrees BBDC (43 degrees earlier).

If the intake valves are closing AFTER BDC,then the 0.100" figures look OK: -16/7 (Primary), -18/9 (Timing side)
That averages out to INTAKE lobe centre at 102.5 degrees ATDC,which would be good.The 0.010" and 0.020" figures don't totally agree,but that's not unusual (they're indicating a 93.5 degree lobe centre).Believe the 0.100" figures.

Although the points of maximum lift look about right (103-105 BTDC),exhaust timings look wrong.
It doesn't look right that the exhaust valves close BEFORE TDC.They should be still open at TDC (about 0.050"),and close after the piston starts moving down.They should have been open about 1/8" at BDC.

I think you'll just have to set both cams so you have about 0.050" lift at TDC,and about 1/8" lift at BDC.If you can't get that much lift at TDC,BDC,maybe the lobes are worn.

#409867 - 12/22/11 4:18 pm Re: Cam Timing [Re: db133]  
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Colorado
It really helped me visualize my measurements when I drew the specs on a copy of BritBike degree wheel.

Edit: It's an A65 BSA.


Last edited by rstar45; 12/22/11 4:22 pm.
#409880 - 12/22/11 5:38 pm Re: Cam Timing [Re: db133]  
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db133 Offline
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How much is the maximum lift? = 0.27

I've gone back over it and I get the same reading give or take a couple of degree (on some). If I have made a mistake I can not see it but mistakes are like that its all a bit tricky to say the least.
Thanks for your help. Like to continue with it and find out all the information that I need to know before I take it apart. just a couple of old knackered cams and followers maybee.

Anyone wana play guess the cam ?

Sorry I do not understand the above picture I only wish I did but the thought was there, thanks. My one is below

Last edited by db133; 12/27/11 9:42 am.
#409954 - 12/23/11 5:39 am Re: Cam Timing [Re: db133]  
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You've got enough cam wear,so you should replace the cams.I think the lowest cam was 0.295" lift.At 0.270",that would mean 0.025" worn off the lobe.If I'm out 0.005",it makes little difference;so I won't search for exact numbers.You haven't worn right through the hardening,there might be 0.020" left.

Good hardening (nitrided cams) didn't happen until about '69.

Rstar45 has used his degree wheel at camshaft speed,not on the crank.That explains the 2 TDC points.All readings would need to be multiplied by 2 to get crankshaft degrees.It's also been rotating counter-clockwise,when the engine is turned in the normal rotation.

Your wheel looks like what I would use,mounted on the crankshaft.The coloured bits are in strange areas,and look like they should be rotated 90 degrees on the wheel.The positions BTC,ATC etc are marked correctly if the wheel is mounted on the timing-side of the crankshaft,via a tube clamped to the crank.
The pointer clamped to the engine should line up at zero when the pistons are at the top (TDC).To the left of the pointer you have ATC,to the right is BTC.

Something is still being lost in the translation.It would be good for you to understand.Look at the points where you show 0.100" lift for the intakes.Approx 17 ATDC (or -17 BTDC) as the valve is opening,8 BEFORE? BDC as the valve is closing.As the valve closes more,to say 0.020" lift,the crank gets closer to BDC and then past BDC.Your 0.020" lift point is before the 0.100" point.There is a similar thing happening with exhaust closing figures.

Does the intake tappet drop to 0.020" lift 40 degrees BEFORE BDC and then rise up again to 0.100" lift at 8 degrees BBDC? I'm sure you can see it doesn't.It's at max lift about 105 after TDC (75 before BDC),and then it keeps closing until it's fully closed (zero lift) some time after BDC.

If we can clear this up,I'm sure you'll be a lot happier and less confused.Even if you change cams,you will find it useful.You'll end up with about 0.070"-0.100" more lift at BDC than at TDC on both cams.

#409961 - 12/23/11 9:32 am Re: Cam Timing [Re: db133]  
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Ref:
The coloured bits are in strange areas,and look like they should be rotated 90 degrees on the wheel.

Sorry my mistake again, I have now revised the picture but I feel its incorrect.

Ref:

Something is still being lost in the translation.It would be good for you to understand.Look at the points where you show 0.100" lift for the intakes.Approx 17 ATDC (or -17 BTDC) as the valve is opening,8 BEFORE? BDC as the valve is closing.As the valve closes more,to say 0.020" lift,the crank gets closer to BDC and then past BDC.Your 0.020" lift point is before the 0.100" point.There is a similar thing happening with exhaust closing figures.

Does the intake tappet drop to 0.020" lift 40 degrees BEFORE BDC and then rise up again to 0.100" lift at 8 degrees BBDC? I'm sure you can see it doesn't.It's at max lift about 105 after TDC (75 before BDC),and then it keeps closing until it's fully closed (zero lift) some time after BDC.


Sorry I've spent some time on the above and do not understand it.


Last edited by db133; 12/23/11 4:47 pm.
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