Valve timing

[Robbie693]

Hi,

I am about to take the head off to replace the gasket (see other post), and I have checked the marks on the cam sprockets at TDC and they are slightly out. Inlet is higher than the top of the head and Exhaust is a bit lower..

As the car was running ok before I took it apart, should I put the sprokets back on in the same position or should I try and get them more accurately lined up (if possible)?

Pics from level with head and slightly higher too show the exhaust marking:

[types26/36]

Robbie,
In my experience the timing marks never line up exactly, well not with standard components anyway, yours look like "par for the course"
You could try when you reassemble to get it closer but I doubt you will, you would have to move it at least one tooth and I think that is 9 degrees and I think you will find then that the marks are much further away unless you are going for offset dowels or adjustable sprockets.
I note you have a split link chain, some people don't like these but I have used them many times with no probs.

[steveww]

I second that. They will not line up exactly with out adjustable sprokets. As long as they are close it will be fine.

Don't forget to back off the chain tensioner. There are also some bolts holding the head on from the underside of the timing chest, make sure you get these sneaky ones Don't ask.

[CBUEB1771]

Robbie,
I agree with the others that the timing marks on the cam sprockets never line up perfectly with the top of the head. However the offset on your inlet cam is a bit more than I am used to seeing. The situation you describe can be the result of the head being surfaced with no subsequent correction of valve timing. Both of your cams are retarded with respect to the crankshaft. This happens when material is removed from the head. The cam centerlines move closer to the crank centerline and the additional slack in the timing chain must be taken up by the tensioner, causing both cams to rotate counterclockwise a bit. Do you know if your head has been surfaced? It may be worth correcting the valve timing with offset dowels. You should not attempt this unless you are fairly experienced. If you are happy with your Elan's performance it is probably best to leave it alone.

[CBUEB1771]

You could try when you reassemble to get it closer but I doubt you will, you would have to move it at least one tooth and I think that is 9 degrees and I think you will find then that the marks are much further away unless you are going for offset dowels or adjustable sprockets.

With offset dowels we rotate the cam with respect to the sprocket. Therefore the valve timing can be made spot-on but the timing marks will still look to be out of alignment.

[types26/36]

Therefore the valve timing can be made spot-on but the timing marks will still look to be out of alignment.

Yes thats true but with the cam timing spot on its usual practice grind out the defunct marks and remark aligning with the top of the head and it is the cam timing we are concerned with.

[stuartgb100]

I do not believe that the sprocket timing marks were guaranteed to be truly accurate in the first place, let alone that over time there may have been sprocket/cam changes and of course, wear and tear/bedding-in etc.

There is surely no better way than to dial in the cams and then
re-mark the sprockets ...... assuming the requisite parameters are known
(eg cam specs etc).

Please correct me if I'm wrong.

Regards,
Stuart.

[miked]

I agree with Stuart. If you dont have the bits buy/borrow and do the check.
Having checked them and learned to do it you will feel good and sure of your facts. If they are wrong and you have to use dowels, again you learn some more. I never did it until I had to. Kept reading and playing. Taking many reading and averaging out.

Also did last engine with vernier spockets. I am only an electrian.

You can make up a nice little steel plate to clamp across the head to mount your magnetic base on. The Wilkin's book is pretty good showing you the procedure and bits.

DTI ?15 - 20 ???
Magnetic base and stand - ?25
Plate mentioned - bit of scrap
Timing wheel - ?7.0

Up to you and how much of a dabbler you are really. Must be, to own an Elan


Mike

[elansprint]

Looks from the second photo if the inlet cam is rotated one tooth clockwise this would be pretty much spot on.
Ian

[stuartgb100]

Ian,

Like I said. if the marks are not accurate, why spend time tryimg to align them.........

dial in the cams and them remark the sprockets.

As Brian says, then remove the old marks

Regards,
Stuart.

[bcmc33]

I just bought a new dial gauge and magnetic stand to replace the one I loaned-out and cannot remember who "borrowed" it. The link shows the source.

http://cgi.ebay.co.uk/DIAL-INDICATOR-BA ... m153.l1262

[twincamman]

step 1 add intake cam and sprocket in place in the chain ----step 2 add ex cam without the sprocket ----step 3 put the sprocket in place with the timing mark correctly located in the chain --step 3 clamp a vice grip on the cam and rotate until the sprocket goes in place [about 1/4 inch or so]--add the washer and bolt ---set the static timing to 15 on a big valve and 5 degrees on the normal tc and its a easy as that -this is done with #1 tdc and the timing mark on the pulley at 0------[applause applause ]the crowd goes s wild ----ed --- thus one of the nagging questions of lotus ownership is answered ---and your all welcome

[Robbie693]

Thanks chaps,

I don't know if t has beem skimmed - I don't have a receipt for it anyway.

I'll see how close I can get it and make a decision then. To be honest I could do with the car back on the road and, as it was running well before the gasket went, I may decide to leave it be.

Thanks for the re-assurance

Robbie

[rgh0]

Robbie

As observed previously it looks like the exhaust cam is spot on and the inlet cam has been assembled 1 tooth retarded versus the marks. Car would run Ok with this incorrect assembly but you may as well assemble it right it when you do the head work and it will run a little better.

Whether the marks were originally accurate or not is another matter but for a road car they are generally near enough correct provided you have a relatively standard block and head and head gaskets so that the assembly height from the crank centreline to cam centre line is standard.

cheers
Rohan

[Robbie693]

Thanks Rohan,

I'll see what it looks like when I get it back together

Cheers

Robbie