Re-timing my cams.

[jimpennock]

Comrades,

Well I have been pondering this for some time and need some expert advice. I have been in overhaul mode for a decade and a half and pulled the sprockets off the cams. The Cams have a single drive dog but the sprockets have several holes to chose from. Gach! and so their position is uncertain. I need to bolt the sprockets back on but don't know what position to put them in.

Here is the current state:
Head has been rebuilt with ew valves and guides and Cam Bearings etc.
Cams are assembled on head but without their drive sprockets.

I suppost that when Piston one is at TDC the cams for that cylinder
need to be at specific angles, I need to konw those angles.
I need to know what direction they rotate as viewed from the front.
I need to understanding how much overlap of Intake and Exhaust

Then, maybe I could figure out what hole on the sprocket engages with the drive dog on the cam's drive flang.

I have the Lotus Service Manual Part No. 36T327 March 1970
The numbers I have are VIN # 45/8861 and Engine # G/18380/B which does not match the way my manual says it should be coded.


Any advice?

Thanks ....... Jim Pennock Marblehead, MA

[rgh0]

Hi Jim

You should not assemble both cams into the head until you are ready to time the cams with the head in place on the block. Doing a test assembly one cam at a time with the head off is OK. The valves can hit each other if both cams are put on and not timed correctly so best to only put both cams on when ready to time the engine after assembly of the head to the block.

The sprockets have 3 holes. Two are the orginal Ford mounting holes for the original in block camshaft, the other is the hole for the Lotus camshafts. You should find the Lotus hole midway between the 2 Ford holes and slightly smaller in diameter.

With the engine assembled and at top dead centre the cam sprockets have lines engraved in the outer rim that line up pointing to each other and parallel with the head top face when the cams are correctly aligned. The sprockets are specific for inlet and exhaust and should be appropriately stamped. If you swap the sprockets the lines point outwards rather than inwards at the correct timing position, the position of the timing marks is the only difference between the sprockets

You need to be careful with the final assembly as turning over the engine or cams without the timing chain in place and correctly timed can lead to bent valves as they hit each other or the pistons.

The Miles Wilkins - Lotus Twin Cam Engine book provides good guidance to all of this and if you have not assembled a twin cam before it is a must read and a lot chepaer than a second rebuild when you get it wrong. While the workshop manual provides much of the same information it is somewhat cryptic and much harder to follow.

regards
Rohan

[vikebo]

Hi,

If I remember correctly (I do not have the book here) the number 4 cam lobes should be pointing inwards when cylider 1 is at Top Dead Center. When you look at the engine from the front, the sprocket on the crankshaft should pull the end of the chain comming directly from the cam sprockets so they should rotate clockwise.

When timing and adjusting the chain tension, you also turn the engine this way to take up the slack.

Eivind

[Dag-Henning]

- with a basic street cam installation, you will be fine with the following set-up :

Cyl 1 in TDC., Cam lobes cyl 1 pointing straight outwards.( - and the lobes on no. 4 will be "rocking", pointing inward/downwards.....)

Most important ; - as Rohan says ; do not turn one cam only when both are fitted !!

After having torqued the cams down, it will be wise to check the timing !

Dag

[SJ Lambert]

Wilkins says to take readings off no.4 tappets

[SJ Lambert]

I sure could use a longer pointer!!

[rgh0]

yes an extension sure helps reach in there

cheers
Rohan

[promotor]

I screw the ball stud off the end of the plunger and then put a thread tap of the same thread in to use as an extension. Does the trick and was easier than finding a bolt to fit.

[types26/36]

my set up with long extensions.

[SJ Lambert]

Nice!

[promotor]

Looking good Brian!

[SJ Lambert]

Made up this platform so that I don't have to reconfigure the DTI as I go from one to the other.