Lotus Elan and Lotus Elan Plus 2 Forums

I have rebuilt the engine, S130 with standard D type cams. Just fitted the chain and the inlet cam is about 1/4 tooth advanced and exhaust cam is about 1/4 tooth retarded. Both Miles Wilkins and Brian Buckland books say the marks are a little variable from new and don't worry.

Not too bothered about inlet being advanced as it will move closer to zero with chain stretch and wear, etc. As this is just a road engine should I use offset dowels to get the exhaust cam near zero or leave as is?

What's the advice from the guru's out there........

Personally I would measure the maximum opening point on each and see where you are versus the spec for those particular cams.

I found that 4 or 5 degree made a noticable difference so I would want to get it a close a possible especially if I'd just built the engine.

....you will always wonder how much better it might have been if you don't

Post up a picture Dave to show the marks on the sprockets in relation to the top of the front cover. Then folk can comment on if it looks about right .

Leslie

I assume you mean that you set the chain with the timing marks exactly aligned and with a bit of slack between the two sprockets (adjuster undone), then the timing changes slightly as you adjust the chain tensioner to get the 1/2" play in the chain between the sprockets? If so, that sounds completely normal to me.

I measured the MOP of the exhaust cam and it?s 2 deg retarded so going to fit an offset dowel. Thinking about the timing marks on the pulleys, their position is set by the chain so they may not align with the timing chest even though the cam timing is correct. I understand the MW and B Buckland comments now!

Well worth considering installing a set of vernier pulleys. Makes life much easier. It can be a real pain extracting the dowels from the camshafts as they are a tight fit. QED have a set of good quality Vernier pulleys at a reasonable price.

I'd second QED pulleys - it does make life much easier!

If you are on a tight budget just fit one! On the intake side of course. The exhaust isn't so important.

Davidb wrote:If you are on a tight budget

Do off-set dowels. Much cheaper option! Why buy that expensive kit when once set you aren't going to change.

elj221c wrote:Do off-set dowels. Much cheaper option! Why buy that expensive kit when once set you aren't going to change.

Based on practical experience I can say that those camshaft dowels are a tight fit and not easily removed in situ. without damaging them. Vernier sprockets are much easier. Note that the distance from crankshaft centreline to camshaft centreline affects the cam timing. Should you ever have the head resurfaced in future this will change and hence the camshaft timing will also change. Not a problem with vernier sprockets as you can easily adjust for it.

Twinc cam timing.

The separation between inlet and outlet cams on the Lotus Twin Cam head measures at 5.833? - or close to.

The timing chain has a pitch of 0.375?

The timing marks on the inlet and outlet cam sprockets align with a roller centre on both sprockets.

If these timing marks are aligned with the top face of the head then there is a tooth in the vertical position on each wheel.
For a tooth to be vertical on each wheel the wheels must be separated by a whole number of timing chain pitches.
5.83? / 0.375? = 15.5 pitches - near enough - so 1/2 a pitch out.

This is quite independent of offset dowels, vernier connections or determinations of TDC or MOP. The relative position of the marks is only governed by the length timing chain top run, the slackness or wear in the top run and the distance between the camshaft centres.

1/2? of slack in the top run does not account for half a pitch.

Assuming the exhaust wheel is set correctly - should the inlet wheel be set with its timing mark just above or just below the head top-face?

Suggestions please!

ccmmccrr