Uprated camshaft timing settings

[villa.1]

Hi All,

 

I'm just about to embark on rebuilding my engine after a rebore ans wanted some advise on instaling the new cam. Cam technical details below:

 

Inlet Timing: 37-63

 

Exhaust Timing: 74-28

 

Duration: 280 degrees

 

Lift: 0.288"

 

Installation Figure: 103 degrees

 

Inlet Clearance: 0.022"

 

Exhaust Clearance: 0.024"

 

Power Band: 2500-6000

 

I know from the manual how to Find TDC but after that i'm unsure about how to find the corect position of the camshaft when i bolt on the timing chain??

 

Any advise welcome!

 

Regards

Steve

[Mike G]

Hi Steve

 

The Triumph Tune literature states:-

 

 

Procedure

 

DISREGARD ANY TIMING MARKS ON YOUR CAM GEARS

The only accurate way to install any performance camshaft is to TIME the profile into the engine using the INLET profile and accurate location of the specific installation position for No 1 piston.

To proceed you must find Top Dead Centre of No 1 piston, then rotate the crankshaft to INSTALLATION figure for your camshaft. (yours would be 103 degrees).

The camshaft only, can now then be rotated, so that No 1 inlet valve is at the exact centre of maximum lift.

Now connect up the timing chain to both of the gears without moving either the cam shaft or crankshaft the camshaft has now been TIMED correctly. ( When I installed my cam, I made a timing disc from some card, put a mark at TDC then used a protractor to mark the degrees I needed for my cam shaft. I then put a hole in the centre, to take the centre bolt ).

 

INSTALLATION INSTRUCTIONS

 

Equipment Required :-

 

A DIAL GAUGE to find T. D. C.

 

A TIMING DISC to find installation degrees

 

1 Set crankshaft at “true” Top Dead Centre accurately using the Dial gauge on number one piston.

 

2 Set the timing disc to O deg, using a fixed pointer on the cylinder block, with the disc firmly attached to the crankshaft.

 

3 Rotate the crankshaft clockwise (normal direction) so that the Timing disc indicates the INSTALLATION FIGURE for your camshaft profile

 

4 Now find MAXIMUM LIFT of No 1 INLET VALVE

This is best carried out with the Cylinder head in position with rockers gear connected and equally “gapped”. Turn the camshaft only-so that the inlet valve is fully open (use the Dial gauge to obtain this accurately).

 

5 Now connect the timing chain/gears. Ensure that the “slack” on the new chain is on the “Tensioner” side.

 

DO NOT MOVE EITHER CAMSHAFT OR THE CRANKSHAFT WHILST CARRYING OUT THIS OPERATION.

6 Try all combinations of the cam gear holes as you should be able to get within a 1/4 tooth of perfect position.

 

Hope this information helps

 

Mike G

Edited March 25, 2008 by Mike G

[villa.1]

Mike,

 

Your a star, thanks for the advice!

 

Regards

Steve

[john.r.davies]

I'm sure that Mike knows this, but timing is not the only way!

 

Another, perfectly reliable method for a six cylinder Triumph is "Equal lift on overlap" (ELoO)

 

At the end of the four stoke cycle, the exhaust is closing and the inlet opening, at the same time.

This overlap encourages the extraction of exhaust gases, and the induction of fuel/air mixture.

Triumph cam shafts do this, and the conventional camshafts are symmetrical, in that the exhaust and inlet cams are the same shape.

 

Now, imagine you look along the camshaft at a pair of E&I cams. At some point in the rotation, the two cams will stick up either side of the midline, like rabbits ears. When they are both at the same height, this is the point of ELoO. It coincides with TDC. (Think about it - it is logical that is should do so!)

 

The Triumph six has three pairs of pistons that rise and fall together. They do so twice in each four stoke cycle, but fire alternately. When both are at TDC, one has just fired and the other is in the middle of the transition from exhaust to induction. Thus the cams will reflect this. Time the cam so that at TDC for one pair of cylinders, one has its caams at ELoO, and the camshaft will be perfectly timed! No need for timing discs! No need for that 'magic number' of degrees to advance the crank, the 'installation figure'!

 

It is best done with TWO dial gauges, set up to measure the lift of No.1 cylinder's cams. Adjust the camshaft so that the cams have the same lift, adjust the crank to TDC for that cylinder pair, and fit the timing chain. Voila!

 

This method will not work for fancy, assymetrical cams.

John

Edited March 25, 2008 by john.r.davies

[piman]

Hello Steve,

 

the hardest part is finding true TDC. Just using a dial gauge at TDC is inaccurate as the crank angle is high relative to piston movement at TDC (and BDC).

 

Using a dial indicator and a timing disc to locate TDC is more accurate. Turn the engine about TDC to get the piston a specific distance down the bore, say .750" and note the angle. Rotate the engine in the opposite direction and again stop the piston at .750" and note the angle. Divide the angle by two and turn the engine that amount of degrees. Now set the timing disc to zero.

 

The other and arguably more accurate way is to bolt a physical stop in the bore. Turn the crank until it won't move, note the angle. Reverse and again turn the crank until it won't move, note the angle, divide by two etc.

 

Alec

[JohnC]

I found that this tape did the job very well in place of a timing disk. Personally I find it easier to read a tape on the outside of the pulley than a disk on the front. YMMV.

 

Print out the tape and stick it on to the outside of the pulley. You may have to fiddle slightly with the printer scaling to get the length exactly right.

 

There's also a cam timing disk on the same site, created by Martti Ojanen. I think Martti posts here sometimes. Thanks Martti!

 

Cheers,

John

[Red 6]

What make of cam are you using? and does it have a name ie fast road/race etc.

 

I would reccomend that you instal the cam before you fit the head, that way you can get an accurate TDC position using a piston stop (a piece of steel bolted across the top of no1 bore) and using the "before and after position and dividing by 2 as described. You might also consider advancing the cam timing by about 4-6deg (inlet 41-43deg) which will increase tourque and mid range "grunt". However you need to start with finding max lift as described earlier to make sure the mfg figures are not already advanced.

 

Cam timing is "very interesting" and i would reccomend you buy a vernier cam wheel from Kent cams. Assembly is easier with it and fine tuning can be carried out at a later stage if required.

[dickymint]

Strongly recommend you buy "How to Blueprint & Build A 4- Cylinder Short Block" by Des Hammill

from Voloce Publishing, after all it's the same plus to cylinders, and is a good reference book when

building you just dip in and out of book as and when required.

Regards

Dickymint

[Tom Fremont]

Sounds like we're dealing with an asymmetrical cam here, so there's no way around using some sort of degree wheel. A couple of targets for y'all to shoot at:

 

1. With the std sprocket there are only (2) positions to choose from.

 

2. The factory TDC mark is pretty accurate; when I checked with the dial indicator method on one example I found it to be exactly on. Considering (1.) above it is good enough for general purposes.

 

I would suggest turning the engine over to check after setting the timing as the slop in the bolt holes will allow for at least a couple of degrees either way. Hence the chosen pair of holes will offer a range of timings and getting the desired one depends upon the relationship when the screws are tightened ( this means that to check it will be necessary to tighten the screws, not just leave them finger tight ). Lastly, I suggest degreasing the cam/sprocket interface, oil the screw threads and set the torque wrench to the high value when installing. The frictional interface does all the driving; if the bolts go into shear mode they will break within a few hundred miles or less, notwithstanding the vestigial locking plate .

[villa.1]

Just wanted to double check something: Is No 1 inlet valve the first one closest to the front of the block?

[TR 2100]

Just wanted to double check something: Is No 1 inlet valve the first one closest to the front of the block?

 

Strictly speaking, No. 1 exhaust valve is closest to the front of the block,

but you've got the right idea - numbered from the front.

 

AlanR