Setting Up Aftermarket Cam And Vernier Pulley

[johnnyboy666 195 1 Cars]

Hello,

 

I've got myself a Piper Rally Cam and Catcams adjustable pulley, to go in my TU3s head, and I've got a few questions about setting the cam timing correctly.

I've read through this thread, which kind of gave me a rough idea : http://forum.205gtidrivers.com/index.php?showtopic=105134

But that's left me with a few questions:

 

1. On a TU, if I lock the flywheel and head using the dowel holes, before I take the head off, would I be right in saying cylinder 1 and 4 are at TDC?

 

2. Assuming that is correct, To get a starting point, I think I would want to

- Remove head with dowels locked in

- fit cam in head with standard pulley fitted (bolt finger tight) with dowel to lock in position

- fit head (both cam and flywheel locked in position)

- somehow carefully remove standard pulley and fit adjustable (set to zero) on without moving the cam?

- Fit belt, again without moving the cam (is that possible?)

 

Presumably from that point, I will have a setting where there should be no valve/piston contact, and the belt in the standard position.

 

I could then remove locking dowels, and slowly rotate by hand to get a zero setting for a DTI guage on the heel of the cam lobe for cylinder 1.

 

Then continue to rotate to TDC and measure the lift. Presumably this will need to be advanced, so at this point, lock crank at TDC, slack pulley bolts off, and continue to rotate the cam until correct lift is found, then tighten pulley bolts.

 

This should get me pretty close to where I want to be unless I've got this all confused somewhere?

 

Am I over complicating this?

 

Thanks in advance!

[johnnyboy666 195 1 Cars]

Anyone ?

[johnnyboy666 195 1 Cars]

Bump! Can anybody help?

[trogboy 17]

Hey bud,

 

My 2 pence worth since no one else is chipping in.

 

1) Yes, pretty much. More precise with a dti on one of the pistons once the head is off (Use a fixed pointer on the flywheel to mark the positions of a set piston height either side of TDC and split the difference to find true TDC). The difference may be miniscule but hey.

 

2) Again yes pretty much. If you are going to be changing the cam you don't need to set everything to TDC before you dismantle, just make sure the liners are clamped before you rotate the crank. When you fit the new cam with the stock cam pulley(bolt finger tight) you'll be spinning it in any case to make sure it turns freely.

 

When the sprocket is on I used a short length of garden wire that wound round and through the dizzy drive slot on the other end of the cam to make a pointer to keep it in pretty much the right spot when fitting the vernier pulley. I guess you could use tippex marks etc. instead. Swap pulley keeping the vernier set to 0, and positon cam back to your mark to get the head bolted down and the timing belt on and tensioned up.

 

Next step is to check the cam timing versus the book figures. IIRC Piper give figures for full lift on no. 1 inlet lobe on the cam as degrees of crank rotation after after top dead center (ATDC). Probably something like 105 degrees for an 8v TU cam. Use a degree disk fixed to one end of the crank whilst at your measured TDC and zero the disk it to a wire pointer etc, so that you can keep a track of crank rotation. Use a dti on the no.1 inlet valve spring retainer to determine where full lift is. Again you'll need to split the difference from either side to accurately find the crank rotation angle for max lift. Loosen the vernier pulley and adjust as necessary by carefully turning the crank to 105 degrees ATDC or whatever is specified for the cam, then re-tighten the pulley bolts. If there's not enough adjustment in the pulley, you've got something wrong - maybe the belt position out by a tooth etc.

 

I might have forgotten something as it's been a long time.

 

Best of luck!

 

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[johnnyboy666 195 1 Cars]

Cheers matey, that's cleared things up a bit since writing the original question, I have made a start, I've rebuilt the head, and have now got the head torqued down, and got myself a dti gauge and a protractor for the crank, ready to have a go at timing it up this weekend hopefully.

 

Would it be wise to adjust the ignition timing at this point or should I start it it up and check if it runs first? I'm just conscious of the warnings I keep seeing about making sure it doesn't drop to an idle during the breaking in proccess

[welshpug 1,661]

you can't adjust ignition timing without starting it, so you're fine there!

[johnnyboy666 195 1 Cars]

Ha, oh yes. Well spotted!

[trogboy 17]

You've got the new cam in then on the vernier? I'd time the cam in to the crank before starting it up.

 

As pointed out, you are going to have to run it to set the ignition timing. I wouldn't get too het up about avoiding any idling at all; you need to set the static advance at idle, just don't mess about!

[johnnyboy666 195 1 Cars]

Yeah I've got the cam timed up to the crank using the standard pulley, then swapped to the vernier with the cam in the same position and fitted the belt. I've turned it over by hand to check for contact and it's all clear. I will time it up properly to the piper spec before attempting to start it, something tells me a 300 cam is going to have a pretty rough idle!

[johnnyboy666 195 1 Cars]

Yeah I've got the cam timed up to the crank using the standard pulley, then swapped to the vernier with the cam in the same position and fitted the belt. I've turned it over by hand to check for contact and it's all clear. I will time it up properly to the piper spec before attempting to start it, something tells me a 300 cam is going to have a pretty rough idle!

[welshpug 1,661]

idle will be fine if you have enough compression and well setup intake.