How to set the vernier cam pulleys.

[top-plumber]

I am thinking of fitting vernier cam pulleys to my S4. Reading about the improved low end performance has convinced me that I should. I could get the green dot pulleys and easily install them but the vernier adjustable pulleys come as a pair and are not much more expensive.

However if I'm to install these pulleys I need someone to walk me through the setting up process with the occasional picture. Have all the required tools for the job just lacking the guidance for the set up.

Thanks

Wayne

[CHANGES]

Hi Wayne,

This is a much asked question and can be long winded to explain in full detail.....

The principals are much the same on most engines which are explained with various video's on youtube.

 

Failing that, I am just about to set a pair of verniers up on a customers 910 engine next week.

If you let me know before then, I can photo during the process, then put together with text to explain.

It won't be a video but it will be on a 910 engine..

Let me know if this will help..   

[top-plumber]

Thanks for the swift reply Dave. That would be the perfect solution for me if it's not too much trouble for you.

I did take a look on YouTube but I wanted to get the info for the 910.

I'm not ready yet as I wanted to make sure I had the ability to tackle the job myself. I'm very comfortable around these engines but can't get this one out of the manual . Thanks again. Regards

Wayne

[CHANGES]

    Setting up Vernier pulley cam timing..

 

There are different ways to do this, but the method I have used for the Esprit 910 is the

fully open method which has never given me any doubt in spot on accuracy..

 

First prepare the engine buy removing the cam covers along with all associated parts.

Also remove all spark plugs to allow the engine to rotate easier, I usually put a wad of

tissue or cloth over the open holes to prevent bits falling in.. If fitting new Vernier’s this

is a good opportunity to change the belt for new one.

 

 

The first and very crucial point is to identify the true TDC point. The marks on the fly

wheel and front pulley are not accurate enough for this job. You will need to fit a DTI to

# 1 or 4 spark plug hole. Then fit a degree dial to the front of the crank with a stable pointer.

Rotate the crank to TDC aligning the dots on the original pulleys. This will insure you are on

the firing stroke for #1 cylinder. Fit a cam lock to stabilise the cams, then remove the belt.

 

 

 

 

 

The crank will move quite freely now which will make the next step easier.    By rocking the

crank each side of TDC slowly you will note the needle on the DTI remains stationary for a

couple of degrees. This is called the dwell, we need to find the centre of this. To do this

rotate the crank till the needle on the DTI stops. Adjust the DTI ‘0’ to the pointer. 

Rotate first clockwise until the pointer just starts to drop off ‘0’ or moves to the first digit.

Make a note on the crank degree dial of this point, then rotate anticlockwise and do the

same in this direction.

The centre of these two points is true TDC. Rotate the crank to this position and set degree

dial to TDC… repeat procedure to insure correct and lock off crank dial..

 

 

 

The next step is to change the cam pulleys for Vernier’s. To stop the cams moving while you

do this you can clamp them in position with small grips

 When new Vernier’s fitted slacken their locking screws. Now fit the new belt. Set the belt 

tension quite tight to remove all the slack especially from the length between the exhaust

pulley and crank. The slip movement in the Vernier’s will allow you to do this.  Now check

crank is still on TDC point, if not reset crank, this should be possible within the movement

allowed on the Vernier’s, if not slacken belt and re-position. DO NOT MOVE THE CAMS.

Once satisfied lock off the Vernier’s on both cams. Your timing is now set as it was before

changing the pulleys. It is now safe to rotate as an assembly, you can  remove the grips

from both cams.

 

 

 

I always set the inlet cam shaft first. To do this I rotate the engine clockwise till the degree

dial shows 104’ATDC on the crank. This will keep the higher tension on the belt between

exhaust cam to crank which is very important. I then lock the exhaust cam with the grips

to hold everything steady with the crank set at 104’ . At this point the overall tension on

the belt is still set tight.

 

 

Next fit a DTI to a cam follower on #4 cylinder (see pic)  Slacken the Vernier on inlet cam

and rotate the cam shaft within the Vernier’s slip  till it indicates MOP.  Zero DTI and rock

the cam as you did the crank to find the dwell . On the std. cam shafts this is about 1.5

degrees. On most Vernier’s a scale is provided which will allow you to find the centre dwell.

When happy lock off the pulley and remove grips from exhaust cam. (The Vernier’s in the

pic’s did not have a scale on, so I etched my own along with an ID signifying which pulley

goes where…E and I ..)

 

 

 

 Most people will accept this as the inlet being set and move on, I prefer to now check the

dwell center against the crank with the belt in its correct tension format first. In most cases

a small adjustment is needed on the inlet cam to re-centralize.

To do this….

Reset belt tension to normal and rotate the engine clockwise approx. 340 degrees,

(to do this you may need to remove the cam DTI and refit )  At this point with the DTI reset

on the cam follower bring the engine towards 104’ ATDC.  Note when the DTI signifies the

start of MOP and read off on the crank dial. This should say 102.5’ . Now continue rotation

till the DTI indicates dwell has ended and read off crank dial again, this should read 105.5’..

If this is so then your 104 timing is set spot on center dwell.  You may wish to go to a digit

either side on the DTI, doing this will give different readings,  but the center value should

always be 104.

Due to belt tension changes you may find a very slight inaccuracy in the reading on the inlet

cam , this can now be corrected by making small adjustment and repeating the last section

again.. It is crucial that the tension should always be taught on the exhaust cam to crank

length when measurements are made and no slack should be allowed to get between the

cams.

Before I start on the exhaust cam timing, I take the engine back to TDC and confirm nothing

has moved then rotate clockwise to the 104’ ATDC point and re confirm the inlet timing.

When fully satisfied I tighten the belt tension so taught all around as before, then I carry

on rotating clockwise to the 104’ BTDC At this point I lock off the inlet cam with grips

insuring no slack in the belt between the cams and from the exhaust cam to the crank. 

The procedure for setting the timing on the exhaust cam is the same as the inlet. When

completed remove the grips, reset belt tension to normal and check the cam dwell against

the crank dial using the same method as previously done with the inlet.. When satisfied

it is all timed correct rotate the engine several times always in the clockwise direction.

Bring back to TDC and go though one final check of all setting there, then at 104 ATDC

and 104 BTDC.

 

Finally mark the new pulleys when at TDC firing on #1,   spanner and torque check all

the fixings worked on and reassemble the rest of the engine parts.

 

 

Some may feel the check and re-checking a bit of over kill and a waste of time.

Unfortunately there is a lot of moving parts and easy to miss something, belt tension

being a big influence.. The reason I initially set up with a tight belt is to prevent

unwanted movement, this does mean however that when the standard tension

returned the inlet cam changes orientation very slightly. This is expected and

compensated for after .  If you set up with the belt at standard tension you will find

your measurements constantly alter depending on the slack point in the belt.  

I find this method works very well especially with 910..

 

 

Hope this helps ...

   

[top-plumber]

That is probably the most accurate explanation I could have hoped for Dave. You have put it succinctly and plainly. Thank you very much. I feel confident that I can carry out this work now.

Outstanding

Regards

Wayne

[Roy Lewington]

Hi Dave, that is a really excellent post. Well done and thanks for taking the trouble.  Cheers Roy.

[Llewelyn82]

Thread bump, but very interesting info Dave!! Fancy setting mine up one day if I swing by with the car?   I'd happily pay obviously!!

[MrDangerUS]

WOW!  Thank you for this comprehensive how-to article!

[rocket63]

Great piece of education Dave. Thanks for taking the time to allow others to apply the correct requirements