Why is TCS engine position shown in the manual at 10 degrees for cam removal?

[thehackmechanic]

Hey, folks, I'm doing my first valve adjustment 700 miles after the rebuild of my '74 TCS. It is an engine with stock cams and a lightly-skimmed head, so I'm side-stepping questions of valve timing and offset dowels and all that for the moment and assuming that the stock marks on the cam gears are good. When I assembled the engine last spring, I used the Wilkins book which instructs you to set the engine to TDC and mount the cam gears so the two marks are pointing at each other and level with the top of the head. All of that went fine last spring.

But when I look in the factory manual for the steps in adjusting the valves and read about removing the cams, it says: "Set the engine in the timing position by aligning the timing mark on the flywheel with the mark on the clutch bellhousing. At this point the timing marks on the camshafts sprockets should be adjacent to each other and level with the camshafts cover mounting face." It references Figure 3, which shows the window in the bellhousing with the pointer pointing directly at the 10 degree mark. It is at this link (http://www.lotus-europa.com/manuals/tcwork/e/tce.pdf) on page 8.

Is this just a mistake in the factory manual? Why would the engine position be set to 10 degrees BTDC instead of TDC either to remove the cams or to align the timing marks on the cams?

Thanks.

--Rob Siegel

[4129R]

You fit the cam sprockets with the engine out of the car, without the gearbox attached.

I have always done it with the pistons at TDC and the lines marked up.

I have no idea why and how you should accurately set the engine to 10'BTDC to line them up. Weird.

[EuropaTC]

Hi Rob,
I'm the same as Alex, I find TDC and then the cam sprockets are almost in line. Not exactly to be honest but pretty close. Offset dowels would get it spot on, but I can't really be bothered for an engine that I only ever use on the roads....... 

Miles Wilkins in his book on the TC engine makes more of finding exact TDC with a dial gauge so  I reckon the manual is mixed up. 

Brian

[thehackmechanic]

Thanks folks.

[jbcollier]

Doing it at 10 degrees just makes it easier to set the distributor accurately and the cams are close enough.  Possibly helpful if you have an “oh f—k” moment.

That said, you can remove the cams in any position as long as you mark things carefully.  I would stick with what you know, TDC.

[4129R]

But how do you set up 10' accurately without the gearbox attached?

It is easy to set the static timing once the engine and gearbox are in place, but I found that accurate timing had to be set with the engine running using a strobe light.

[EuropaTC]

But how do you set up 10' accurately without the gearbox attached?

I doubt many people even try Alex.

Out of curiosity I took a look at the various manuals I've got for the TC engine, the Elan & Europa ones, plus the Miles Wilkins book.  The text in the Europa manual isn't identical to that in the Elan which specifically mentions TDC, and whereas the Europa has a diagram showing the flywheel set to 10deg, the Elan doesn't. The Elan has the sketch attached here, which shows TDC, pretty much what Miles says in his book anyway.

Then you look at the details for timing and they're all over the show depending on cams and carbs, from 5 deg to 12 deg.  So I reckon the 10 deg. illustration is just one of those minor mistakes that didn't get caught in proof reading. 

Brian

[4129R]

IMHO, the marks on the front belt pulley cannot be regarded as accurate.

Only the marks on the flywheel (if it has been bolted to the crank correctly) can be accurate, and on a Europa, they can only be checked with the gearbox attached through the hole in the bell-housing.

[jbcollier]

The manual is suggesting you set it at 10° for an inservice valve adjustment, just in case you're a futz with the chain.

Mr. 4129R is correct that crank marks are not particularly accurate, but then, neither are the cam sprocket marks.  To be precise, you need to find the actual, exact TDC and then use the valve timing specs, a dial gauge, and special venier sprockets or offset woodruff keys.  This can make a huge difference on a full race engine.  Not so much on a stock engine.

[Grumblebuns]

This is what I remembered from my last valve adjustment. The timing chain is slack, the marks on the cam sprockets are lined up, then you tighten up the cam chain. At this point the sprockets move and the marks on the sprockets no longer line up. I then re-loosen the chain and rotate the sprocket(s) one tooth, re-tighten the chain and check for mark alignment. Is what I'm doing correct?

Joji Tokumoto

[jbcollier]

The engine is at indicated TDC, the cam sprocket marks line up, and the chain slack is correct = you're fine.