camshaft lift check and valve opening distance

[dblenk]

Is it as  simple as putting a DTI on the rocker and checking the displacement ??

i think my USA 6 might have had something put in other than std

thanks

David

Edited June 14 by dblenk

[dblenk]

well i got 0. 246" on the DTI maybe not that accurate but looks like a better cam

i did have 110BHP with std USA low comp head so always thought something had been done

see what the UK head and new manifold do, the old manifold had 6 sensor tubes in it which restricted exhaust flow ?

David 

Edited June 14 by dblenk

[dblenk]

if the valve opens around 0.25" is that about right for a 6

i did fit a 3.4" head with the shorter pushrods 8.125 (8.3" came out although it states 8.3 for a CR head in the moss catalogue)

thks

David

Edited June 14 by dblenk

[Ian Vincent]

A quick look at the Newman cams range shows their road cam has a cam lift of 0.25” giving a valve lift of 0.375”. Their offerings increase the cam lift in steps of 0.02” up to their tarmac rally cam at 0.29”. They do also offer a full race cam with 0.32” of lift. So I would say that your measured valve lift of 0.25” is on the low side.

Rgds Ian

[dblenk]

Ian

thats what i was thinking but taking off the thk USA head and fitting the 3.4" thk head i used the shorter pushrods which were the same as the TR5 (i measured my TR5 ones)

however the pushrods with the thk head were 8.3"

so to get more lift and valve opening i  could fit the longer 8.3" it does say in the moss catalogue the 8.3" were fitted to a CR engine

i did measure the tappet at the valve not the pushrod so 0.25" at the valve divided by 1.5 gives a cam lift of 0.167" ????

or perhaps someone can show me the error of my ways

David

[dblenk]

in addition to above are all the rocker shaft assemblies the same for any 2500 engine eg 1.5:1 ???

just checked moss USA they do a shortened pushrod by 0.120" bu they dont state the length of the std pushrod fitted with a 7.5:1 ratio head

i took 8.3" long pushrods out but were these shortened or std  ???

david

Edited June 16 by dblenk

[Ian Vincent]

I can’t see how changing the pushrod length can affect the valve lift. And I’d be surprised if the rocker ratio was any less than 1 : 1.5.

Rgds Ian

[dblenk]

9 minutes ago, Ian Vincent said:

I can’t see how changing the pushrod length can affect the valve lift. And I’d be surprised if the rocker ratio was any less than 1 : 1.5.

Rgds Ian

i am thinking the valve opens as a factor of length of pushrod plus cam lift therefore cam lift is what it is and happy with what i got before changing heads

it started as a check to ensure my geometry is ok and obviously i have  a few doubts

david

[Ian Vincent]

David,

The pushrod is merely the link between the surface of the camshaft lobe and the rocker. Varying the length of the pushrod will not change the amount of lift that the cam lobe provides.

If you place your DTI on the top of the rocker at the pushrod end and rotate the engine you will measure the camshaft lift. If you place the DTI at the other end of the rocker you will measure the valve lift. Assuming that you have a standard engine, the valve lift will be 1.5 times greater than the cam lift. 

Rgds Ian

[dblenk]

HI

Ian will set it up again the engine ran great before i changed the head so its a check i must be missing something somewhere

i will try pushrod and valve end

i think its a std cam (1976 USA was the same as the UK CR version)

cheers David

[Waldi]

Hi David,

If you have a skimmed head (to increase the compression ratio), a couple of mm of the height are gone. This is why there are different lengths of push rods. If you would use “US spec car” rods they are longer that “CR or CP spec car” rods. 

As Ian states, the rod length has nothing to do with  valve opening.

Waldi

[dblenk]

Hi

checked the movement on the cam at the pushrod on a inlet valve

i got a reading of 420 (reading is 0.01mm) so 4.2mm (chinese dti from ebay) 0.165" no cam lift matches that on chris witir ???

1.5 rocker equals 6.3mm opening the valve

from chris witor cam lift CR is 0.24" 6.096MM cp CAM IS 0.25" 6.35MM

WITH A 1.5 9.144 VALVE OPEN CR 9.5MM WITH A CP

like i said earlier performance was fine but started to check maybe i should ignore and get on with it ???????????????

[Ian Vincent]

Hi David,

It’s easy enough to calibrate your DTI. I would do that first and assuming the DTI  is correct, I’d be thinking about a new camshaft. 

Rgds Ian

[dblenk]

just checked my TR5 as the rocker assembly is removed and got 0.25" which is correct

i will remove the rocker assy tomorrow and check the pushrod up and down so its clear lift not trying to keep a DTI on the arc of the rocker

keeps me busy

David