Lotus Elan

Not pulling through 5K RPM

PostPost by: chickenstock10k » Mon Apr 22, 2019 2:56 pm

Alright, I think I am starting to wrap my head around what needs to happen here.

How do you keep the cam (that isn't being adjusted) and the crank in place while you are adjusting the cam that is off though?
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PostPost by: nmauduit » Mon Apr 22, 2019 4:23 pm

chickenstock10k wrote:Alright, I think I am starting to wrap my head around what needs to happen here.

How do you keep the cam (that isn't being adjusted) and the crank in place while you are adjusting the cam that is off though?


to be on the safe side I would check the workshop manual... the principle is first to find TDC (which may or may not correspond to crank pulley mark at 0), then time exhaust side (which is done with the chain under tension between crankshaft to exhaust sprocket), then to do inlet timing (chain under tension between the 3 sprockets). When I do it, I turn the engine over CW several times to take the slack back (the tensionER being on the inlet side). After valve timing has been duly set and checked and tensioner set back to proper chain tension, the ignition timing needs to be checked, too.

ps: I don't think a few degrees off alone would be enough to prevent a stock engine in decent condition to free rev above 5k ... but it seems there are a few points to check and clear before any further tuning can be attempted.
Last edited by nmauduit on Mon Apr 22, 2019 5:35 pm, edited 2 times in total.
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PostPost by: h20hamelan » Mon Apr 22, 2019 5:19 pm

I am no expert

https://performanceparts.ford.com/downl ... Timing.pdf

Some good information for thought

This one opens some other thoughts

https://thumpertalk.com/blogs/entry/227 ... am-timing/

B Buckland seems to state. Cam lobes on #4 cylinder point toward each other.

I believe light force, forward and backward of cams. Will indicate closed #4 valves because of springs. Though I am not sure if it is that easily noticeable.
As you add tension from the tensioner. The slack must come from somewhere. Most likely intake. Therefore, if You consider one cam to be advanced. One might consider advancing intake as tension will spin intake cam backwards.
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PostPost by: Chrispy » Mon Apr 22, 2019 8:30 pm

It's pretty easy. Turn the engine over until the crank is at TDC and the two No.4 cam lobes are rocking towards the centre on the lifter. Slacken off the chain tensioner. Remove the crank sprocket on intake cam. Chain will be slack, adjust the cams so the little lines align with the top face of the head. Put the chain back on. Tension it back up and turn it over a few times. You'll probably have to re-time the distributor.
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PostPost by: JJDraper » Mon Apr 22, 2019 9:43 pm

+1 on all the other advice, especially avoiding dropping bits down the cam chain tunnel...

This may help..viewtopic.php?f=15&t=25730&start=

Some pics a a similar story to yours.

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PostPost by: billwill » Mon Apr 22, 2019 11:28 pm

chickenstock10k wrote:Alright, I think I am starting to wrap my head around what needs to happen here.

How do you keep the cam (that isn't being adjusted) and the crank in place while you are adjusting the cam that is off though?


With the engine at TDC, undo one of the cam bearing caps and put in a piece of cardboard from a cereal packet across the bearing surface. Then put the cap back on and tighten just over finger tight. The camshaft will not then move while you are fiddling with the sprockets and chain.

REMEMBER TO REMOVE THE CARDBOARD before trying to spin the engine.
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PostPost by: Bigbaldybloke » Sat Apr 27, 2019 12:33 am

May sound daft, but are you sure your rev counter is reading correctly now you have changed the electronic ignition, there are loads of threads on here about problems with rev counters indicating incorrectly or erratically with electronic ignition. Have you checked the revs in top gear against the speed to see if they agree?
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PostPost by: Quart Meg Miles » Sat Apr 27, 2019 10:10 pm

69S4 wrote:When I time my cams via the sprocket marks they don't line up exactly at tdc (about 1/2 tooth's worth out) so I guess I need some offset dowels. If one tooth out gives the flat above 5k characteristic under discussion would correcting my 1/2 tooth error make any noticeable difference? Anyone got before and after experience?

My Inlet is correct but Exhaust (the one re-marked by Lotus) is nearly half a tooth out but the cam is in the right place (I measured the timing of the lobes). This seems to be a common problem (a thread about a month ago) but I had already bought, but not fitted, an offset dowel which is redundant.
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PostPost by: mgfollett » Sun Apr 28, 2019 5:13 am

How fresh is the fuel? Sounds crazy but I've had a similar problem with my Europa, ready to pull hair out after trying almost everything else felt stupid when discovered fuel was the problem!

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PostPost by: chickenstock10k » Fri May 03, 2019 4:57 pm

Alright... as an update...

I thought I had skipped a tooth but after getting the hood off and really looking at it. I think I was just having a hard time getting a good angle for visual inspection I confirmed at the valve and it looks like the valve timing is OK.

I checked the RPM on the tach against a timing light and it seems to be about right. My new theory is that with the installation of a set of headers I may have improved flow enough to be leaning out the strombergs at the top end.
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PostPost by: gjz30075 » Fri May 03, 2019 7:03 pm

Maybe install an AFR meter to see what's really happening; or, if you have a 'rolling road' or chassis
dyno shop near you, they usually install some temporary probe to check afr.
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PostPost by: nmauduit » Fri May 03, 2019 7:53 pm

good yo know that valve timing is good. Now again just to be sure : symptom is the engine does not free rev above 5k rpm (actual calibration reasonaly checked via external tacho, light meter or otherwise), correct ?
2 quick thoughts in case not investigated already:

- do you have a rev limiting distributor ? if no valid lead this way then

- have you checked actual fuel pressure at the carbs while running it to full rev ? I have modified a banjo bolt with a fuel pressure gauge to that end, cheap and helps clearing the ground sometimes...

good luck (and keep us uptaded)
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PostPost by: 2cams70 » Sat May 04, 2019 2:15 pm

Please forgive me for saying but you don't seem to be going about this very scientifically!!
You installed a new distributor. Correct (Y/N?)
Engine looses top end after installing new distributor. Correct (Y/N?)
You have reinstalled old distributor to determine if top end is restored (Y/N?)
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