Lotus Elan

Adjustable cam gear install

PostPost by: collins_dan » Sat May 12, 2018 8:04 pm

Is much more complicated than it was on my son?s Miata. What is the basic procedure? Seems like front cover needs to come off? Any recommendations for basic settings to start with? Degree advance for intake and retard for exhaust? Any advice appreciated. Thanks, Dan
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PostPost by: billwill » Sun May 13, 2018 12:28 am

My description of my claytest happens to mention in between some of my photos how to refit the chain and sprocket wheels after putting the head back on.

lotus-twincam-f39/clay-test-checking-clearance-between-valves-pistons-t26441.html?hilit=clay

My cam sprockets happen to be the vernier adjust able type, which I think is what you are referring to.

It is not necessary or desirable to take the front off the timing case except to access the waterpump or layshaft sprocket.

Then I put the tensioner spring and adjuster back in, loosened.

DSCN3554 (Large).JPG and
Chain tensioner adjuster back in.



Then I fitted the cam sprockets and chain, starting with the exhaust sprocket and verifying that I had a clear run of chain from the crankshaft sprocket at the bottom to the cam sprocket, and that the straight run up from the crankshaft is reasonably tight when the sprocket is on the cam and the timing mark is level with the centre of the top of the head. This ensures that I am not one-link out of place. Taking extreme care that I do not drop a washer or bolt down into the sump I inserted the sprocket-securing bolt and did it up loosely. (While doing this I find it best to put the spring washer and big spacer-washer on the bolt, then hold the bolt head in a socket spanner with just an extension piece in the spanner, no ratchet or tommy bar, so that I can support the washers with my other hand.)

Then I did the same with the inlet sprocket. Then the tensioner adjuster was screwed in to tighten the chain until I had just half-inch up & down movement in the chain at the top between the sprocket wheels. You will see from the pic that I have those nice fully adjustable sprocket wheels in my engine. That was one of the mods, Rob Morley did for me back in about 1998.

Checked that the timing marks on the sprocket wheels are both aligned correctly, if not I might have had the inlet sprocket one-tooth out of place.

DSCN3555 (Large).JPG and

Bill Williams

36/6725 S3 Coupe OGU108E Yellow over Black.
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PostPost by: collins_dan » Sun May 13, 2018 3:50 pm

Thanks. That?s what I was hoping. Dan
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PostPost by: collins_dan » Mon May 14, 2018 12:10 pm

Any general experience that anyone can share would be great. I am just trying to improve street performance, and sounds like this can positively impact high end hp, but negatively impact idle. Just curious to hear others experiences. Thanks, Dan
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PostPost by: rgh0 » Tue May 15, 2018 12:11 pm

If your running standard cams set them as precisely as you can to the Lotus recommendation. If running non standard cams set them precisely to the manufacturers recommendations. Then take it to a rolling road dyno and set up the carbs and ignition to get the most out of your fuel your using and the standard cam timing . The decide if you still want to play with cam timing. If you do find a good dyno guy who understands this stuff and play with it on the dyno, not cheap but very good learning to spend a day on the dyno doing multiple runs with changes in cam timing.

Alternatively read a lot of books and play with adjusting the timing yourself and doing road tests to determine what changes you like.

Directionally there are changes that give more top end HP or more mid range torque for specific cam when moving from the standard specs but these differences typically are subtle and while they will show on a dyno and potentially in lap times on the track they are much harder to feel by seat of pants on the road

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PostPost by: collins_dan » Tue May 15, 2018 3:20 pm

Thanks, Rohan. That's is actually the plan. I had another shop install Q360 cams (replacing L2 cams) a few years ago during a head gasket replacement and they have always been a disappointment. I am now wondering if the issue is that the Q360 cams specify 105 degrees after TDC and 110 degrees before, whereas L2 cams are 102 after and 102 before. Maybe cam timing was not set properly for the Q360 cams. I have the spec sheet from q360 and they are going to see how close its running to that as a starting point. Sounds like adjusting cam timing with the engine in the car is challenging. Engine adjustments are way out of my wheelhouse. :? Dan
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PostPost by: jono » Tue May 15, 2018 3:44 pm

Dan,

I've just re timed my QED 360 cams with adjustable pulleys so If I can do it you will be able to do it!

Mine were advanced 4 degrees on the inlet and 6 on the exhaust and I re timed them to the recommended QED figures.

It was more torquey before hand but now revs much more willingly and is far more eager to go to 6k or more than it was before.

On balance, and it's a very fine line, I probably preferred it as it was with a bit more torque.

You will need to make up a plate to mount your DTI on a magnetic base. It will probabaly be more fiddly with the engine in the car in terms of mounting the degree wheel (my engine was out an on a stand)

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PostPost by: CBUEB1771 » Tue May 15, 2018 4:07 pm

collins_dan wrote:Sounds like adjusting cam timing with the engine in the car is challenging.


The process is quite simple with the engine in place, once you have a means of adjusting cam timing installed and have a good understanding of the safe range of adjustment available to you. The first step is to check where you are now, with comparison to the cam supplier's recommendation. There are many sources of variation in cam timing, the first being reduction in cylinder head thickness by facing. If you are more than a couple of degrees away from the cam manufacturer's recommendation then installation of "vernier" cogs, offset dowels or offset bushings will make sense. If the intent is just to recover the cam manufacturer's recommended setting this can be done with the engine in place as long as you don't drop anything down into the timing chest. I don't know a great deal about the QED 360 cams but the lift suggests they are probably intended to be a straight replacement for Sprint cams and 110 degree lobe centers (inlet and exhaust) would be about right. If you want to experiment with cam timing you should start by checking for valve/piston and valve/valve interference through a range of cam timings. Several good methods have been described here and I won't try to recapitulate them now. You probably want to check clearances through a range of about 5 degrees before and after the manufacturer's recommended lobe centers. This is most easily done with the engine out of the car and on a stand. I have a system of offset bushings. It was necessary to reduce the diameter of the dowels where they engage the cam drive cogs and also to enlarge the dowel holes in the cam drive cogs to accept bushings. The bushings have "center" holes that are offset from the bushing's true axis. I have a range of bushings that allow the cam position to be offset by as much as six degrees in one degree increments. I find that changes of two degrees make a noticeable difference in the torque-speed characteristic. As Rohan suggests, you will need to experiment carefully to find the settings that suits your driving habits best.
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PostPost by: jono » Tue May 15, 2018 6:29 pm

See attached
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PostPost by: CBUEB1771 » Tue May 15, 2018 7:43 pm

Thanks for posting the QED360 specifications. The dyno sheet is interesting in that it reveals that a crank-trigger ignition system was used. I would be very interested to know what that contributed to the performance.
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PostPost by: jono » Tue May 15, 2018 8:04 pm

Not sure Russ but by coincidence I use the same system (Ford Edis with a Megajolt).

This is the dyno curve for my own car using QED 360 cams timing advanced and detailed previously in this thread. I never used conventinal ignition so cant postulate on what contribution is made by the wasted spark system but is starts and runs very well.
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PostPost by: collins_dan » Tue May 15, 2018 8:28 pm

Russ and Jon, thanks.
Jon, Your dyno sheet looks great to me. Power is right in the range where I would use it most often. Just to be clear though, since I'm a rookie at this, the 4 degrees advance on the inlet and 6 degrees on the exhaust was that to get to the 105 after and 110 before, which are QED's specs?
Thanks, Dan
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PostPost by: jono » Wed May 16, 2018 6:35 am

Dan,

No those are the QED figures that I re timed the cams to. The original engine builder had previoulsy advanced the timing from those figures (which produced the dyno curve I posted).

Please see my post here:

lotus-twincam-f39/camshaft-timing-t41697.html

Cheers

Jon
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