Cam Pulley Alignment

[perksy]

Hello All

The TC is now going back together and I've fitted a new timing chain from Burtons today

I've verified TDC by using a DTI & long probe down the spark plug hole of number one cylinder
The mark on the crank pulley and the appropriate mark on the cover line up fine at TDC

The correct pulleys are fitted to the appropriate camshafts

After adjusting the chain to the correct tension, the timing marks on both cams are exactly 2mm below the flat face of the timing chain cover

Putting a spanner on the crank pulley the engine turns over fine by hand

Am I trying to be too exact in hoping that the pulley marks would line up exactly with the flat face of the timing chain cover?

Thanks

[Foxie]

The pulley timing marks are probably pretty close to spec, but are not guaranteed to be exact. You may need to check the actual cam timing with a dial gauge and timing disk. Offset dowels (cheap but fiddly ) or vernier pulleys (expensive, but simple ) can get it spot on.

[512BB]

Over the years I have found that usually one mark is slightly above the cover and one slightly below when using the standard sprockets, but rarely both marks below the cover, but 2mm is really not much, however you could be a tooth out on one sprocket. If you are, you will soon know, as the engine will run, but it wont rev freely.

Leslie

[rgh0]

Over the years I have found that usually one mark is slightly above the cover and one slightly below when using the standard sprockets, but rarely both marks below the cover, but 2mm is really not much, however you could be a tooth out on one sprocket. If you are, you will soon know, as the engine will run, but it wont rev freely.

Leslie

As heads and blocks are machined this misaligment with one above and one below happens. I have seen engines with both above or both below as in this case and always put it down to just inaccuracy in the sprocket marking. The engine should run OK

cheers
Rohan

[512BB]

'As heads and blocks are machined this misaligment with one above and one below happens'

It may well do, but I have about 20 heads here, collected over 40 years, and all of them had never been remachined prior to removal from the block, yet hardly any of the timing marks matched up exactly horizontal with the top of the timing case. They rarely did with standard sprockets, even from new.

At some point, I shall build my complete, new old stock Big Valve engine, inc nos block and head, cams, crank, everything, and report back on how those marks line up.

'and always put it down to just inaccuracy in the sprocket marking'

I am not sure what you are saying here Rohan. If you look at my picture, every sprocket is line marked bang on identical to each other, so no inaccuracy there, but are all the timing lines in exactly the correct position for every engine, even when the engine was new? Definately not. For that to happen, each sprocket would have had to have been marked after the engine was assembled, then the sprockets removed and then stamped, and that was just not going to happen.

Leslie

[rgh0]

The lines shown are accurate in a centre location between two teeth. Now line up the spockets on an exact centre and line up the dowel hole and see how accurately the teeth line up.

The 0.040 inch Lotus machined off the big vavle head would technically have required a relocation of the sprocket markings to compensate. Does any one have a known orginal Sprint sprocket to compare to an earlier known Non Sprint sprocket to see if Lotus bothered ?

cheers
Rohan

[perksy]

Thanks to everyone for your comments

Rohan, Thank you, I was hoping your were going to see this post and your comments, Photos etc on the forum have been a great help to someone rebuilding their first Lotus TC

[Craven]

Surely only down to chain link centre accuracies ie overall distance between the sprockets.

[billwill]

Unless you fit offset pegs or 'vernier' sprockets, You can only change the relative timing of the cams by one-sprocket (one chain-link) anyway, so getting the marks together as close as possible and 'facing' each other will be right.

The chain from the main crankshaft pully to the output-cam sprocket and the chain from the top of the output-cam sprocket to the top of the inlet-cam sprocket should be taut. All slack taken up by the chain tensioner. if you do that and the timing marks are facing each othe, that is the correct setting.

The timing will change slightly when the head gasket compresses.

This topic of mine, though it is nominally about 'clay-testing', describes fitting the head onto the engine and fitting the timing chain.
viewtopic.php?t=26441&p=175063

This is mine with 'vernier' sprockets.