A cautionary tale ......

[stuartgb100]

Went to re-shim the cams on my Sprint this weekend, lined everything up. took the clearances, removed the cams and changed the shims as necessary.

Re-torqued the cams, double-checked the clearances, and then went to refix the sprockets.

Close inspection revealed THREE sets of timing marks on each sprocket !

Consternation and venting of many expletives. Neighbour rushed round thinking car had fallen on me.

So, which set of marks were the sprockets on when I removed them ?

Now, the cams could be original Sprint, or reprofiled Sprint ( there are certainly 2 grooves on the connection boss behind the sprocket).

I can only see to put a timing disk on the crank pulley with a pointer, then establish opening and closing degrees of the valves (not that easy with the engine in-situ)........ then compare that with standard Sprint spec cams and go from there.

Anyone better ideas ?

Regards,
Stuart.

[steveww]

How close are the different timing marks to each other?

You can get a good starting position for cam timing just by looking at the cam lobes. With No 1 cylinder at TDC, looking at No 1 cam lobes from the front of the car the lobes should be pointing outwards away from each other.

IMHO The only way to set the cam timing properly is with a dial gauge and adjustable sprockets.

[rgh0]

If you know the specified lift at Top dead centre you can also use that as a setting point for the cams. If dont have this data for sprint cams but someone may.

Generally I dont like setting the cams at this point as it involves moving the cams when the valves are close to the pistons and very easy to bend a valve if you get it wrong during the setup process but it is a recognised technique and many people do it.

Fitting a timing wheel on the crank pulley is difficult with the engine in the Elan due to the chassis location. For in car setting I mount a small diameter timing wheel on the front of the cam sprocket. Incidently I make the timing wheel by printing a nomral large timing wheel photo onto a printable CD which is just the right diameter to fit.

cheers
Rohan

[garyeanderson]

What about another set of cam sprockets (used or new)? You should be able to get it fairly close

Gary

I had a think over some hot cakes and honey, being the thrifty lad that I am. How about cleaning up your sprockets and bring them down to your local Lotus Motorfactors and matching them up with a pair of new ones and put a colored mark on your olds ones as to which mark is the correct one?

[stuartgb100]

Thanks for the replies.

I compared the sprockets side by side. On each there appears to be one mark that is more pronounced (more definite, if you will). I think these marks are likely to be the original timing marks.

so I lined them up with inlet on the left and the mark at 3 o clock, and the exhaust on the right, with the mark at 9 0 clock.

On the inlet there is one other mark at about 9 o clock and another mark at about 3.30.

On the exhaust it's the opposite......... one more mark at about 3 o clock, and another at about 8.30 pm.

Checked the original invoice for the ground-up restoration. Sure enough it says: "To reprofile cams, reduce base circle."

Hmmmm.

I think I'll try and convert these o clock values into more accurate measurements in degrees. See if that gives any clue.

Regards,
Stuart.

[stuartgb100]

Thanks for the replies.

I compared the sprockets side by side. On each there appears to be one mark that is more pronounced (more definite, if you will). I think these marks are likely to be the original timing marks.

so I lined them up with inlet on the left and the mark at 3 o clock, and the exhaust on the right, with the mark at 9 0 clock.

On the inlet there is one other mark at about 9 o clock and another mark at about 3.30.

On the exhaust it's the opposite......... one more mark at about 3 o clock, and another at about 8.30 pm.

Checked the original invoice for the ground-up restoration. Sure enough it says: "To reprofile cams, reduce base circle."

Hmmmm.

I think I'll try and convert these o clock values into more accurate measurements in degrees. See if that gives any clue.

Regards,
Stuart.

[Frank Howard]

On the inlet there is one other mark at about 9 o clock ...On the exhaust it's the opposite......... one more mark at about 3 o clock

Stuart,

It appears that the DPO didn't realize the sprokets are different and mounted them on the wrong cams. Then he marked them accordingly.

[stuartgb100]

Timed everything up using what I believe to be the "original" sprocket markings ......... lined up perfectly after adjusting the timing chain adjuster.

Wouldn't fire at all, but while cranking over there was the suggestion that it was too far advanced.

Double checked the settings when at TDC on compression on no1 and the marks were good. Looked at the nearby marks (not the ones at 180 degrees opposite). Sure enough, if they were aligned it would have the effect of retarding both cams.

Will try that tomorrow night.

Regards,
Stuart.

[poiuyt]

Once you get the car set up, paint the correct mark with Wite-Out or some other permanent mark. You won't have to go through this in the future.

Steve B

[SJ Lambert]

And I presume that no.1's lobes pointing away from one another translates to No. 4s rocking on the cylinder.

How close are the different timing marks to each other?

You can get a good starting position for cam timing just by looking at the cam lobes. With No 1 cylinder at TDC, looking at No 1 cam lobes from the front of the car the lobes should be pointing outwards away from each other.

IMHO The only way to set the cam timing properly is with a dial gauge and adjustable sprockets.