Lotus Elan

Valve Timing - some Dumb Questions

PostPost by: Dilkris » Tue Feb 25, 2020 3:51 pm

I have been rebuilding a big valve engine, (sorry it is from a Europa), for some time. Now retired, progress on the rebuild is dictated by finances which are generated by selling "stuff" that I collected over the years by having access to more money than sense. I am now at the stage where I am ready to offer the head back to the block and embark upon (I think) the dark art of checking valve timing. I have read this well discussed topic at length on the forum AND made dog eared pages within the Miles Wilkins "Byble". I "think" I am beginning to understand the approach but I have the following questions I am still uncomfortable with regarding definitive answers.

1. To prevent any valve/piston contact, BEFORE initially offering up the head to the block I assume I have to have No.1 piston at TDC AND the inlet and exhaust sprockets so positioned with the timing marks facing each other - correct?

2. I understand the significance of establishing an accurate TDC and not relying totally on the crank pulley and timing case marks to achieve this, but can I rely on the camshaft sprocket indicators (marks) or do I have to go through the inlet/exhaust camshaft Open/Closes BTDC/ABDC dance....?? (Note: this is a road engine I am building and I am using vernier sprockets)

3. Finally, in Miles Wilkins book, page 146 at the bottom it reads, "When setting the valve timing, make sure both camshafts are rocking on number four cylinder". That does this term "rocking" mean exactly? Does it mean when the cam lobes are "just" making contact with the cam follower? (Cigarette paper test..?)

Thanks in advance for your help.
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PostPost by: JonB » Tue Feb 25, 2020 4:11 pm

OK, don't worry it is much easier than you think.

No 4 cam lobes should be pointing at each other.
No.1 cylinder should be at the top of its stroke (check with a screwdriver poking out of the spark plug hole, or use a dial gauge).
Sprocket marks should be facing each other, roughly level with the top of the timing chest.

Don't worry if the sprocket marks aren't exactly lining up. The chain, if stretched, can alter this slightly.. as can the amount of slack between the cogs. Hence you can't really rely on their accuracy. Not sure how that bodes for verniers. In my case I was trying to ensure I hadn't slipped a link when I reassembled my engine, so close enough was good enough for me.

Regarding TDC, a post I read said to turn the engine until your indicator (dial gauge or screwdriver) stops lifting, then note the crank position. Continue turning until the indicator starts dropping and note crank position again. TDC is roughly between the two positions.

Also, be aware that if you took the cylinder head off, you will need to check and alter the valve clearances.
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PostPost by: richardcox_lotus » Tue Feb 25, 2020 7:37 pm

I don’t believe Verniers have sprocket indicators. AIUI, They are used to proscribe a slightly different arc, individual to each wheel. Col Croucher from here has a good video on YouTube on valve timing. Probably worth a look.

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PostPost by: 2cams70 » Tue Feb 25, 2020 10:21 pm

To get the timing approximately correct with vernier sprockets first temporarily set the engine up using the original marked sprockets. Don't fully tighten any sprocket bolts leave them loose so they are easy to remove again. Without turning the engine replace with the vernier sprockets whilst adjusting them so the sprockets go on easy with the engine in this position. Do not turn anything!. In this position the vernier sprockets should be set up approximately correct. Once this is done you can then go through the process of setting them up exactly by turning the engine over, determining TDC, measuring lift, crankshaft degrees, etc.
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PostPost by: Dilkris » Wed Feb 26, 2020 7:47 am

Thank you to the 3 replies so far - I really appreciate the response but the comments I have received do not answer my original 3 questions, but shoot off addressing issues which I have not questioned. :shock: :shock:
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PostPost by: JonB » Wed Feb 26, 2020 9:31 am

OK, dude.

Dilkris wrote:1. To prevent any valve/piston contact, BEFORE initially offering up the head to the block I assume I have to have No.1 piston at TDC AND the inlet and exhaust sprockets so positioned with the timing marks facing each other - correct?


I didn't answer this explicitly, but I explained how to get the engine into the correct position (that is, valves and engine at TDC). I should have said that doing this pretty much guarantees you won't get any valve / piston interference on refitting the head, unless head or block have been incorrectly machined. But it seemed pretty obvious you knew that or you'd not be worrying about how to set TDC.

Dilkris wrote:2. I understand the significance of establishing an accurate TDC and not relying totally on the crank pulley and timing case marks to achieve this, but can I rely on the camshaft sprocket indicators (marks) or do I have to go through the inlet/exhaust camshaft Open/Closes BTDC/ABDC dance....?? (Note: this is a road engine I am building and I am using vernier sprockets)


Again, I explained how to set up TDC roughly. 2cams70 gave a good suggestion to help you get the engine setup without worrying about the vernier positions.

Dilkris wrote:3. Finally, in Miles Wilkins book, page 146 at the bottom it reads, "When setting the valve timing, make sure both camshafts are rocking on number four cylinder". That does this term "rocking" mean exactly? Does it mean when the cam lobes are "just" making contact with the cam follower? (Cigarette paper test..?)


I answered this: "No 4 cam lobes should be pointing at each other." In practice they will be angled slightly downwards. For most people (that is, those without vernier pulleys) this will be enough, as the spacing of the timing chain links will determine how accurately you can set the relative positions of the lobes.

Incidentally, Miles further explains in the sentence where he uses the term "rocking on no. 4 cylinder" that "the camshaft sprocket marks will be in line at the front". There's also a nice diagram on page 147 showing the front of the engine at TDC with all marks aligned.

Dilkris wrote:...but the comments I have received do not answer my original 3 questions, but shoot off addressing issues which I have not questioned. :shock: :shock:


If you do what has already been suggested you will get a running engine which you can use as a basis for adjusting the verniers.

One thing you haven't made clear is if you have the original cam sprockets as well as the vernier sprockets. If you don't, or your verniers have no alignment marks on them, then there's a problem..
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PostPost by: 512BB » Wed Feb 26, 2020 11:15 am

Dilkris wrote ' To prevent any valve/piston contact, BEFORE initially offering up the head to the block I assume I have to have No.1 piston at TDC AND the inlet and exhaust sprockets so positioned with the timing marks facing each other - correct?

No, you do not have to do it like that, indeed, I never do. If you fit the head with the camshafts already bolted down, if you are not careful, there is a chance that you could bash a valve head on the block face and tweak it. I make sure that all the pistons are half way down, or up :D the bores, and then lower the head onto the block and tighten. Obviously, it then does not matter where the cams are, in relation to the pistons, if indeed if you even have the cams fitted at the time, which I don't.

Once the head has been tightened, I then insert long round wooden dowels, all the same length, into each plug hole, so that I can see exactly where each piston is when I start to set the timing and fit the camshafts.

Now I really must get back to the markets, to see how much my wealth has shrunk this morning :?

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PostPost by: JonB » Wed Feb 26, 2020 11:22 am

Oh by the way, at the bottom of page 146 is a diagram showing what Miles means by "rocking on number four cylinder". Couldn't be clearer.

Leslie, that's a jolly good point regarding piston positions.
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PostPost by: nmauduit » Wed Feb 26, 2020 11:44 am

Dilkris wrote:1. To prevent any valve/piston contact, BEFORE initially offering up the head to the block I assume I have to have No.1 piston at TDC AND the inlet and exhaust sprockets so positioned with the timing marks facing each other - correct?


I understand from this that the camshafts may already be on the head when offering it to the block : I prefer to offer the head without the camshafts so that I am sure I'm not going to risk bending a valve (esp. if the engine is in the car) - then when the head is in place, cyl #1 at TDC, the camshafts can be put back at about the right angle (this wont be the exact angle as the springs will tend to turn them to a resting position depending on actual profile)

Dilkris wrote:2. I understand the significance of establishing an accurate TDC and not relying totally on the crank pulley and timing case marks to achieve this, but can I rely on the camshaft sprocket indicators (marks) or do I have to go through the inlet/exhaust camshaft Open/Closes BTDC/ABDC dance....?? (Note: this is a road engine I am building and I am using vernier sprockets)


Road or race, it's always best to get accurate valve timing : in order to make the most of vernier sprockets I believe it is worth the extra effort of timing accurately the TDC, then timing each camshaft in turn. This is not that much work though requires the setting of a depth gauge to do it comfortably, and in turn not only the engine will likely be better tuned than when off specs but one can rest assured that at least this part has been done right.
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PostPost by: jono » Wed Feb 26, 2020 1:08 pm

do it once, do it right :D
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PostPost by: Dilkris » Wed Feb 26, 2020 4:32 pm

Thank you all for your input; for the record the head is off the block, (obviously) and "yes" I do have the original inlet and exhaust cam sprockets because "yes" the vernier sprockets have no external indicators.

With regard to the comment:- "Oh by the way, at the bottom of page 146 is a diagram showing what Miles means by "rocking on number four cylinder". Couldn't be clearer."

I am well aware of this, but this is not a diagram it is a sketch and moreover Miles Wilkins uses the term "rocking" - why did he not simply say "camshaft noses on number 4 should be facing each other"??? This of course would be a very liberal and un-exacting term with regard to camshaft orientation and as such I believe that the "rocking" term he uses has an exacting definition.(Possibly when the "closing ramp" section of the cams are in contact with the cam followers, and facing each other?)

Anyway, I have not been addressed as "dude" for many years and on that note I will continue to research the "rocking" definition and consider this thread with regard to my 3 simple queries closed.
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PostPost by: JonB » Wed Feb 26, 2020 4:38 pm

Yes, well... by all means be petulant (as above, and in your original reply) but just remember we are only trying to help you.
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PostPost by: Davidb » Wed Feb 26, 2020 6:28 pm

One way to position the camshafts is to imagine them as one cam!
If the 'one' cam was fitted how would the lobes on #4 look? They would look like the diagram at the bottom of page 146 superimposed one on the other and you would not easily be able to turn the camshaft is the answer.
My first racing ohc engine was a Coventry Climax FWA and the factory manual instructions for installing and timing the cam were exactly as described: put the camshaft in place with #4 lobes as described with #1 at TDC. I never had a problem and won races-never knew what degree wheel was back then...
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