Help! Validating my Valve Timing!

Hi, I am in the throes of setting up my valve timing for the very first time on my 1968 Plus 2 and just looking for a sanity check on my calculations, assumptions, interpretation and next steps. I have read many previous posts and also referenced Miles Wilkins book but still require guidance / validation.

Being new to this, I was largely expecting relatively small adjustments would be required using offset dowels but the results I am getting are on a much more significant. Am I missing a fundamental understanding here?

My Cylinder head has recently been reworked to the following spec:

• Skimmed to Sprint spec
• Sprint Inlet Valves
• Standard Exhaust valves

I have fitted QED Q360 Camshafts, set all valve clearances to spec and initially set valve timing to original baseline (No1 Piston/Crank at TDC, Camshafts both rocking on No.4 cylinder, my original timing marks are all in alignment). So far so good…

QED have provided the following technical details for Camshaft settings:

• Inlet Fully Open: 105 degrees after top dead centre (ATDC)
• Exhaust Fully open: 110 degrees before top dead centre (BTDC)

Using a DTI Gauge and Timing Wheels I have taken the following measurements multiple times (but I will measure again). The DTI has resting on the No.4 cylinder (exhaust first and then inlet). I have also factored in dwell etc…:

• Inlet Open @146 degrees after top dead centre (ATDC)
• Exhaust Open 98 degrees (BTDC)

In summary this would suggest:

• Inlet has 41 degrees variance from recommended specification (Actual 146 vs. Target 105 degrees)
• Exhaust has 12 degrees variance from recommended specification (Actual 146 vs. Target 105 degrees)

As mentioned above, I was largely expecting relatively small adjustments would be made using offset dowels but these numbers are more significant. At a high level could these be directionally accurate or is there something I am doing wrong?

Assuming that the numbers are directionally ok, would I make the major adjustments by moving by 4 teeth and 1 tooth respectively and then remeasuring for the minor adjustments?

Go back and repeat the process until it works. it sounds like you skipped a few teeth when fitting the sprockets and tensioning the chain

Thanks Rohan. What could be the expected range that I should hit, so that I recognise a successful outcome? As mentioned, based on original valve timing and marks, everything seems 100% correct and the engine is turning perfectly by hand. But my measurements seem way out…

Your expectations that it should be within a few degrees is correct if not there is something wrong with how it was fitted or your measurement of the end results. The QED 360 cam is very similar to the original Sprint cam so i am not sure why QED specify a different timing but QED have a number of errors with their quoted cam timing from what I can see.

cheers
Rohan

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Thanks Rohan. I will return to the garage tomorrow and go back a few steps and re-measure. Based on your feedback, I think it may be due to the way I have lined up the timing wheels on the Cams (which I thought would make it easier to read - but I think I have screwed it up ;-)… More to follow…

Hi Rohan,
The more I measure and the more I read the more I am confusing myself further so wonder if I can approach this a different way with your expert guidance.

  1. QED Q360 Camshafts fitted with all all valve clearances set
  2. No.1 Piston/Crank at TDC
  3. Inlet and Exhaust Camshafts both pointing towards each other (rocking) on No.4 cylinder
  4. Original Timing marks all seem to in alignment
  5. I have a DTI Gauge and Timing wheel

QED have provided the following technical details for Camshaft settings:

  • Expressed Period: 280 degrees
  • Maximum Cam Lift: 0.355"
  • Inlet Fully Open: 105 degrees after top dead centre (ATDC)
  • Inlet Lift @TDC: 0.134"
  • Exhaust Fully open: 110 degrees before top dead centre (BTDC)
  • Exhaust Lift @TDC: 0.112"

What is the sequence of steps I should now follow to set-up to these recommended steps? What would Rohan do ;-)?

Thanks!

The No4 cylinder is at TDC on overlap and should have the specified lift at TDC on the inlet and exhaust. Check that with your DTI. Then fit the timing chain and tension it being sure not to move the cams dont worry if the timing marks do not line up. I normally do this with the sump off to ensure i engage the crank sprocket correctly with the run from the crank to the exhaust cam tight, you can do with the sump on but its trickier to get right Rotate then engine and then check the maxium opening degrees of the No1 cylinder inlet and exhaust to see how far its off the specified values then use offset dowles ( or adjustable sprockets)to set this correctly

cheers
Rohan

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Thanks Rohan.

I will head back to the garage in the morning and try again. Just to replay my understanding from your feedback, from where I am at right now:

  1. Remove Timing Chain
  2. From current TDC, with both lobes pointing at each other on Cylinder 4, rotate the Inlet Cam to achieve lift of 0.134" (perhaps about 30 degrees clockwise)?
  3. From current TDC, with both lobes pointing at each other on Cylinder 4, rotate the Exhaust Cam to achieve lift of 0.112" (a lot more clockwise duration in the region of 90-100 degrees clockwise)?
  4. Refit chain and tension
  5. Measure MOP against specs on Cylinder No.1, from same TDC point on crank

Is that directionally correct?

Thank for your help and sorry to be a pain. The engine didn’t start when I bought it 2 years ago and the car has been off the road since 1980. Its been a long journey to get to this point with many learning curves along the way and it would be a nightmare to damage this newly refurbished cylinder head through my lack of understanding at this stage!

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I think you misunderstood . The idea was with engine setup as you have it now with the timing marks meeting then check the lift of the valves at No4 cylinder they should be close to the QED quoted values for lift at TDC. Remove the chain if fitted and adjust the cams slightly to get the specified values on No4 . This should be only a few degrees of cam movement. Once you have done that then refit the chain. You may have to move the engine crank or cams slightly to get the chain to fit. The you can rotate the engine and check the degrees for maximum valve opening on what ever cylinder you want, I normally use No1. You should find you will be a few degrees out in the specified maximum opening point and then need to use offset dowels or adjustable sprockets to achieve the specified value

cheers
Rohan

Thanks Rohan. I think what may be confusing me is that exactly as I have it set right now both the inlet and exhaust are reading zero lift. I have zero overlap.

For example, if I now take the chain off and I then rotate the intake camshaft clockwise (about 30 degrees at the crank) it will then meet the QED inlet lift value of 0.134"at TDC. This is on the inlet valve opening cycle.

If thats correct, what do I then do on the exhaust side?

Here’s an image of current position with Crank at TDC and chain removed.

I presume you are talking about No4 cylinder. You need ot get the valves on that cylinder at the specified TDC lift. If you have the lobes pointing to each other then you need to remove the chain and rotate the inlet clockwise and the exhaust anti clockwise to achieve the desired TDC lift on No4 cylinder for both valves. I am surprised this requires a 15 degree cam movement away from where the timing marks line up but thats possible I guess

cheers
Rohan

Thanks Rohan - the sounds like a clear plan. The engine wasn’t starting up to begin with and has now had a skim, reprofiled cams, and a brand new chain so perhaps that accounts for the delta!?

I added an image above just to help you visualise my current alignment at No.4.

15 cam degrees is a lot to be out from the original sprocket markings but without knowing the full history and detail of all the work done on the engine over the year anything is possible. Thats why its also best to go back to square one and work from to specified cam openings at TDC and MOP

Ok Rohan, here is a quick update:

  1. Removed Timing Chain
  2. I have now made the minor adjustments to both cams as discussed early to ensure Inlet lift @TDC of 0.134" and exhaust lift @TDC of 0.112" by rotating the cams small amounts clockwise and anti-clock wise respectively. Visually it is a very subtle change from before with each tappet just being slightly lower (2-3mm)
  3. I marked the back end of the cams and the cam caps with Tippex to track any movement when reassembling the chain.
  4. Chain fitted with good tension. Everything rotates freely and Tippex marks all line up
  5. When using the DTI gauge I am getting the following measurements:
  • Inlet Valve Fully Opens (initially): 100 degrees ATDC
  • Exhaust Fully Opens (initially): 105 degrees BTDC

If I compare these results with the QED Data sheet then I am close now (Inlet Target 105 and Exhaust 110). I believe that would require 2 x 0.030" offset dowels to adjust. Does this sound directionally sound?

I also performed the MOP calculations which throw things way off (122.5 and 82 respectively), so I have reached out to QED to check whether their Target data (Inlet/Exhaust Fully Open) is based on when the valve fully opens initially or based on MOP. I’m waiting on a reply from then but any insights would be most welcome.
Thanks again,
Ewan

This is all about what I would have expected. Use offset dowels as needed to achieve the final cam timing for MOPs

I am not sure what you mean about MOP “calculations”. MOP is a measured number and your measured numbers seem to make sense

cheers
Rohan

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Hi Ewan,

Degree wheels that I have seen are typically non-monotonic, i.e. BDTC side is usually marked 0 to 180 running CCW whilst ATDC side is typically marked 0 to 180 running CW. Are you happy you have got your sums correct as I certainly found it was easy to get a sign wrong when setting my cams up (assuming you’re doing the dwell compensating method of measuring a certain lift offset either side of the peak.)

Iirc the 100 and 105 figures sound about in the ballpark; one question I couldn’t see covered above though is are the sprockets on the right cams? I think the timing marks are one tooth different between them, and in my case the sprockets weren’t obviously marked. Someone else can confirm if I’m mistaken.

Cheers

Will

How are you measuring the MOP point ? You say fully open “initially” what does that mean ? You need to measure the degrees at a set lift point that is a little lower than the MOP before and after the MOP to get the true MOP by dividiing half way between the two

cheers
Rohan

Thanks Will. Yes, my degree wheel is marked that way too - which takes a bit of thinking about :wink: and yes definitely got the sprockets on the right cams (the exhaust has “Ex” etched on it Slowly getting closer I think!

Hi Rohan,

The MOP point is possibly where I am getting confused between many of the documented methods (Lotus Forums, Miles Wilkins etc…) vs. the data provided by QED :

  • Valve Lift @TDC eg. 0.134" for Inlet
  • Valve Fully Open e.g. 105 degrees ATDC for inlet

One of the things I was unclear on is whether the QED data providing the valve lift has already factored in the MOP point calculation (QED know the profile of the cam after all). I asked them the question and the answer didn’t really help (but perhaps I asked it the wrong way). Question and Response was:

  • Question: "Just a follow-up question from yesterday. Is the data on the data sheet relating to “Inlet Fully Open” and “Exhaust fully open” based on when the valves first fully open or on the Maximum Opening Point (MOP) calc?
  • Response: “The information of the data does relate to inlet and exhaust fully open”.

In any case, here is an explanation of what I did and the data I captured:

  1. When I turn the crank clockwise from TDC the inlet valve reaches maximum lift (initially) at around 100 degrees ATDC
  2. If I continue to turn the crank clockwise it stays at the same maximum lift until around 145 ATDC

If I then take the True MOP approach does this then give me a MOP of 122.5? Or am I calculating this wrong?

Thanks!