250 cam timing, again....

Hi All
I have been grinding along with some work on a 250 Lusso, the motor is going back together pretty well, now I refitted the camshafts and sprockets with their respective etched markings lined up as it came apart, it has had a new timing chain and various ball races that live in the front end have all been replaced but the sprockets all appeared to be in good shape went back in, my problem is that the right hand cam as in cyls 1 to 6 appeared retarded, whilst 7 to 12 lined up as I hoped. Now the flywheel is marked up with a twenty seven degree before TDC mark which as far as I understand it is for cam timing, as in the inlet starts opening 27 before TDC on overlap, so is it fair to assume that with the clearances set correctly the cam roller will bind as the 27 degree mark is reached. The 250gte resource site has a fairly long winded method which uses a degree wheel attached to the flywheel but can the marks on the flywheel be used to accurately set the timing. I did check the cam timing using the cam wheels of the inlet valves in conjunction with the flywheel markings, the left hand cam is very close to being spot on in relation to its etched marks, the right cam, as in 1 to 6, was retarded if the cam sprocket was fitted with its etched mark lined up with the cam etched mark, the cam etched mark was out of alignment with arrow on the cam bearing. I reset the right hand cam using the mark on the flywheel and obviously had to move the cam sprocket a couple of bolt holes, I think, and now both cams are matched timing wise using their respective 27 degree marks, is this ok? I am a little puzzled about the etched markings not lining up on the right side but there is no movement on the bolt holes for fine adjustment unlike an Aston which has slotted holes and you set cam timing using a dial gauge on the valve itself to measure the lift.
Can someone suggest a basic way of checking and setting the cam timing or was the method I have used adequate, thanks Bill.

 

PM sent
Chris

 

If the intake opening AA 27 and exhaust closing CS 16 events of the valve train match the marks on the flywheel (assuming the flywheel is installed correctly), then you should be good to go. I alway check that the #1 piston is really at TDC when the flywheel PM1/6 mark lines up with the pointer, as I have seen cars with flywheels improperly installed.

Brian Brown
Patrick Ottis Co.

 

Hi All
thanks for the replies, I will recheck it again and will employ a dial gauge to see pretty much exactly when the rocker arm moves for both inlet and exhaust, tat should do it. I was a little concerned that the original mark on the right hand cam sprocket did not line up as such but I suppose there may be a little wear on the sprockets. Lastly can anyone confirm the number of teeth on the water pump sprocket and the auxiliary drive sprocket as they both have the same spline, but a different number of teeth. I am certain I did not get the two mixed up during cleaning but now may be the time to make sure before its all buttoned up, thanks Bill.

 

Hi
Water pump drive 18 teeth, Aux drive 20 teeth. Best to time cams to max lift.
Chris

 

Here's the aux drive sprocket in mine, sorry for the quality of the photo.

john
Image Unavailable, Please Login

 

Hi All
thanks for the replies about cam stuff, I checked it by sticking a dial gauge on the inlet and exhaust rockers and figure if the inlet starts moving when it should and the exhaust stops moving when it should it can't be a million miles off. so both cam wheels needed resetting to get it sorted but the little etched marks on the cams had not appeared to move at all despite the timing have been advanced which kind of shows they are a little vague and open to interpretation, I can only assume that the cam wheel markings were off because the sprockets have worn a little allowing the chain to sit further into them, either that or I got the left and right cam wheels mixed up.

 

Hi Bill, The etched cam marks are just good for initial setup but you still have to time by measuring cam lobe position relative to flywheel marks like you're doing. There's a book, I think the one by Rousch always on eBay, that has a good description of the process. If you reset the chain tensioner to take up chain stretch, I found cam timing is surprisingly sensitive to that adjustment.

 

I never use the original etched marks that are on the cam sprockets, they were there from long ago when the engine was first assembled, and are useless for setting the cams. Only the etched marks on the cams themselves are good for the initial installation, but as you have found out they are not very accurate. A large change in cam timing results in only a small movement of that mark in relation to the cam bearing cap. Using a degree wheel and dial indicator is the best way of setting the cam timing. Using the flywheel works well as long as you have confirmed that the PM1/6 mark is accurate when the #1 piston is at TDC, and then check the cams using the AA 27 and CS16 marks.

I aways check both the intake opening and exhaust closing events on each individual cam, as sometimes cams have been changed or reground and you can have one dead on, and the other is way off.

 

Correction to my above post: The book that I found to contain a good supplement to cam/ignition timing procedures in the factory books was "Ferrari Guide to Performance" by Allen Bishop.