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I’m sure there’s a simple answer to this one but I don’t know it! All available guidance for the 2 Litre states that clearances should be 4 thou for the normal camshaft but 8 thou for a high lift one. Seems to me that, as the valves are the same (in length and expansion coefficient) and they are operating in the same thermal regime, there is no need for this change, given its unfortunate effects of reducing the open period and making an already clattery engine yet noisier.
Wise words please!
H54 John
I discussed that with my friend John (B29) who told me this: the experience was that at least with modern fuels you can give the old cams a bit more overlap but should combine that with 6 thou inlet / 8 thou outlet clearance. I am running this setting at the moment (in combination with a downdraught head). For the improved profiles he recommends 8 / 8.
I only can imagine that optimising the valve timing gives more power, so more heat, therefore requires more gap (which reduces slightly the before increased overlap). Probably one can try anything between 4 and 8 depending on the timing of the cams, but at the risk of burning a valve. Is there a way to find the minimum (cold) gap before burning the valves (0 hot gap) ?
Thanks for the interest Peter. I’m sure you are correct, the flaw in my assumptions is that the thermal regime is unchanged – it must be the case that the more mixture in, the bigger the bang and the more heat produced. So it will have been perfectly reasonable to play safe and increase the gap, thereby ensuring that the valve definitely closes under all circumstances. This would be especially so as the only penalty would be some increase in noise level and possibly some reduction in power. But to me the recommended doubling from 4 to 8 has an arbitrary look about it and I do wonder whether anyone has bravely tried other settings, whether with standard or high-lift cams.
BTW, these musings were prompted by a recent wedding where the car, an early Rolls, was so quiet that someone nearby wondered whether it was electrically powered. I was a bit envious.
Hi All,
You must not assume that the only reason for valve clearance is to compensate for expansion.
Cams are designed with opening and closing ramps of differing profiles and having differing attributes.
cooking engines i.e. those used for shopping for food need to be quiet so the wife can be heard giving instructions and therefore the engineer designing the cam incorporates a “quietening ramp” this can have several forms but the most common is a slight increase of the cam’s base circle dia at about 100 deg to full lift and staying all the way to the opening ramp. For this reason it is also not recommended to adjust your tappets at any other position than 180 deg from full lift on the appropriate cam lobe.
A gentle opening is also incooperated so cam to follower “slap” is reduced. RR were very good at this and their quality control was good also which helps to allow for tight valve clearances.Fast road engines etc. are driven by men. Men don’t mind not hearing the wife?s instructions and in fact revel in the fact that they have raughty exhausts and a little noise from the engine so they can feel the power they normally do not have at home. Performance cams open the valves faster and let them close faster, they rarely have quietening ramps. (Bentley designed his race cams with 0.025″ clearance and they work well) Heat is surely one reason for increased clearance but only a very small part of it.
Valve recession is also another factor we must consider, the faster we rev and the higher the lift, the more the hammering of the seat and the more the valves recess. 1 or 2 thou can happen very quickly, especially on a newly built engine and it’s much much better to have to ask the wife to repeat her last instructions than have to stop and listen to her telling you repeatedly that you should have gone in the Renault because your valve has just burned out on the motorway due to too tight settings.
Won’t go on now so have fun and keep it at 8 John, although I know Clair is wonderful to listen too ;o)
Please give her a kiss from me.Regards,
JulianThanks Julian. I must admit that as I read your post, with much interest and amusement, I did wonder whether it had been passed by Ann for censorship!javascript:InsertTagsMenu(‘ 😉 ‘, ”, ‘bbsmileys’)
JH
Absolutely John,
It’s her constant beatings that keep me in line and knowing my place!J 😆
Sorry to come late to this discussion but my advice would be to stick to .004″ Much as we love our cars not all Lagonda engineering was done with critical analysis and followed up by comprehensive testing. I suspect that doubling the tappet clearance between the standard and blown engine was just an “off the cuff” decision. I run a high lift cam and frequently take the engine to 5000 rpm. Never had a problem with a burnt valve and haven’t needed to adjust the tappets for the last two seasons. Still getting 160 psi compressions. Large tappet clearances will only reduce the valve opening and may even cause the valve caps to fall off. Not to mention upsetting the wife !
I have been helping Tim Gresty reset the camshaft timing on his 2 litre and I now realise that some of the section I wrote in the revised handbook is misleading. 4 thou tappet clearance is right for the standard 14/60 and speed model cams which have duration of 225 and 236 degrees respectively and should be timed to open at Top dead centre. However the Leonard Reece cams and Newman cams are designed to have a duration of 256 degrees with 8 thou tappet clearance . If 4 thou clearance is used with these later cams the duration goes up to approx 270 degrees .
It is also very important to have the inlet valve open position well before top dead centre at say 15-18 degrees and then double check that it closes 58-60 degrees after bottom dead centre. Any later closing will result in blow back through the carburettor at lower revs. This was what Tim had with his engine because I had timed it to open too close to top dead centre and the performance was very poor.I run my 2 litre with 50 degrees overlap IVO at 20 BTDC, EVC at 30 ATDC With .004 tappets I get 265 deg opening on both cams. This means that IVC at 65 ABDC and, yes, I do get a modicum of “reverse pumping” at revs up to 2300 BUT once over these revs the full effect of the cross flow head becomes apparent and it “sings” You pays yer money and you takes yer choice !
Just joined the Club & seen this. A similar discussion came up on the E Type forum a while back; Jaguar changed the cam profile at some point, and altered the clearance from 4 I & 6 Ex, to 12-14 for both. I questioned why they had found it necessary to double the gap.
The consensus was that otherwise the valve timing would be wrong with the new cams. I made myself unpopular by refusing to buy this explanation. I cannot accept that Jaguar would re-design the cam and then say “Oops, now the timing is out but if we open up the gaps we can get it back to where it should be.”
Others suggested that they opened the gap because the previous gap had been too small. Once again, I find it impossible to believe that it would take forty years for such a shortcoming to become apparent.
Still no idea why they did it though – it remains one of life’s mysteries!Oh, I forgot to say, the Lagonda 2 litre engine is complicated by the fact that the rockers bear directly on the camshafts with a profiled pad. The profile of this pad is critical to valve timing and opening profile, and as these wear unevenly (as mine have) this will throw everything out, regardless of clearances or actual cam timing.
H 54 John wrote: ….. the flaw in my assumptions is that the thermal regime is unchanged – it must be the case that the more mixture in, the bigger the bang and the more heat produced. So it will have been perfectly reasonable to play safe and increase the gap, thereby ensuring that the valve definitely closes under all circumstances………
Ah, but I think there is a flaw in this argument also – the instruction book gives a gap of .004 hot OR cold! So it may not be as susceptible to temperature variations as you imagine?
Good point Hugo and thanks for the interest. I still think there’s an arbitrary look about the doubling of the tappet clearance but I chickened out in the end and went for the 8 thou recommended for my LMB cams. This despite Tim Wadsworth’s wise words and his engine throws out about double the horsepower of mine.
Incidentally, the other day I put my car on a local dyno and was a bit disappointed that, despite a higher CR and fancy cams, the peak output calculated back to the flywheel was just the 60 bhp claimed by Lagonda in 1927. Torque fell off a cliff at about 3200 so Tim’s downdraught head must be very, very effective to let him rev to 5000.
Best of luck with the project, it sounds a great buy. I look forward to admiring it at Wisborough Green before long.
I think I’d take any dyno figures with a grain of salt. They’re good for comparative testing, but as an indicator or absolute BHP I’m not so sure. I rebuilt a Harley engine for a friend once, and, much to my surprise, it went like an absolute rocket (the reason I was surprised was that he had bought a kit off eBay, like you do, and it wasn’t really the spec he wanted, as you could tell by just glancing at the big fat cam lobes). Anyway, he put it on a dyno and complained that the figures were lower than the manufacturer claimed. I gave him the same advice as above.
Anyway, I am new to Lagondas so have no experience of these interesting engines. But having read Tim Wadsworth’s post, it seems that he is the living proof that .004″ will work ok.
As I said earlier, though, the profiles of the rocker pads are critical to the effective cam profile. I suspect that any wear here will upset the performance.
What is the spec of your engine?
My car (EWF 99) is a hybrid – it looks like a 2 litre Speed Model but started off in life as a 14/60 saloon. It has high comp pistons & twin SU’s. My cams and rockers are worn, but not terribly, and that will be another job for another day – when I get my new down-draught head from Wessex.
Right now I am trying to figure a way of sticking the dynamo on the side of the engine – I fitted a new water jacket side plate which the Club says is ‘ready to fit’, and in a sense it is. But after I had spent hours drilling out the snapped off bolts (a task abandoned by the previous owner), then enlarging the holes in the side plate so it would fit where the bolts had been drilled slightly off by the previous owner (who had tried to do it in situ), and then sealing it all up with RTV including fibre washers under the bolt heads, I then noticed that I was missing a couple of tapped holes in the side plate for the dynamo strap! The old plate had turned to dust so I had nothing to compare. I’m hanged if I’m taking that plate off again so that’s another little challenge before I put the engine back in (good job I noticed it before I did!).In my long rambling post, I forgot to ask what condition your cams & rocker slipper profiles are in? I notice you said the torque drops off a cliff above 3,200? Sounds like it’s running out of puff, doesn’t it?
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