Reprofiled camshafts - Opinions?

[nebogipfel]

Gentlemen,

I note that QED and others offer a camshaft reprofiling service and I was mulling over getting my camshafts reground to Sprint spec'

Have you had this done? Does it result in weakened shafts and the need for excessively thick shims?

I would be interested to hear what you think

[ardee_selby]

John,

What's the starting point for this "upgrade"? Standard to Sprint Spec? S/E to Sprint spec?

Are you also contemplating the concomitant changes? Larger inlets? Skimmed head? Re-jetted carbs?

[elanman999]

John,
I had some SE cams (1.2" base circle) reground to QED360 cams and IIRC the base circle of those is approx 1.1" so all the shims will be approx .05" more than before. I timed them up and they perform well and no problems in 18K miles.
I'm sure QED would be able to give you a more accurate figure.
One thing about the 360 cams is that there are some data sheets out there (from QED) with the incorrect lift at TDC values (silly hi numbers) on so check this if you go this route.
Cheers
John

[nebogipfel]

Richard, I'm embarrased to say I can't remember if my cams are std or SE. So it would be one or the other to Lotus Sprint profile

Performance is not a huge priority for me these days but I am thinking about a rebuild in the nearish future and thought a set of Sprint cams at that stage might be worth doing. I doubt I'd bother with the valves because I suspect the difference in BHP is marginal. The head has been lightly skimmed so the CR is likely to be up on standard but again I'm not looking for a huge power boost or fretting about putting it on a dyno.

My concern was less about BHP figures and more about the pro's and con's (if any) of reprofiled cams?

Thanks

[ardee_selby]

Nothing untoward with the reprofiling I've had done in the past.

On my twink, Vulcan engineering took them (S/E) to their version of sprint spec. VL107's

This was, however, part of a complete head rebuild. Not sure if I would have bothered with a cam change on it's own.

[elancoupe]

I have run reground cams for almost 30 years - no issues at all.

[nebogipfel]

Nothing untoward with the reprofiling I've had done in the past.

On my twink, Vulcan engineering took them (S/E) to their version of sprint spec. VL107's

This was, however, part of a complete head rebuild. Not sure if I would have bothered with a cam change on it's own.

Thanks Richard,

My head had new guides, seats recut, etc not too many miles ago but I would go through the head at the same time.

If I rebuild the block I was really thinking of giving the old girl a bit of a boost without going mad. Everything I've read suggests that the "big"? valves add little to the twink and that the lion's share is Cam and CR.

J

[nebogipfel]

I have run reground cams for almost 30 years - no issues at all.

Thanks Mike, that's encouraging

Ditto John.

[UAB807F]

If I rebuild the block I was really thinking of giving the old girl a bit of a boost without going mad. Everything I've read suggests that the "big"? valves add little to the twink and that the lion's share is Cam and CR.

Hi John,

Yes, I've read the same thing about the big valve being more of a marketing exercise than an essential part, and it was only the inlets as well, the exhausts are the same.

But on the other hand, when I changed my cams for sprints many years ago I did re-jet & re-choke the webers and put the larger valves in at the same time. I didn't increase the compression ratio because even in those days 5* was disappearing but I wanted to get as close to sprint spec as practical and of course the head was off for new guides/seats so an extra 4 valves made little impact on the budget. Maybe if I'd been replacing the cams with the head in-situ I'd just stick to cams & carbs, leaving the valves until the head came off.

Brian

[ardee_selby]

A relevent thread from May 2009. Well worth revisiting:

elan-plus-f13/sprint-cams-t18318.html

[rgh0]

Reprofiling in itself is not a problem and the resultant cam is effectively returned to as new condition but with a smaller base circle. You need to replace or at least regrind flat the face of the followers if they are cast iron and in OK condition and use the correct running in procedure and assembly lube / running in oil to reseat the followers and cams together. You should not attempt to regrind steel followers (all new followers supplied in the last few years have been steel as far as i am aware) as the nitrided hard surface is very thin and you cannot to afford to remove it without renitriding and in this case you may as well buy new followers.

Before getting the work done determine the new base circle the grinder will produce and ensure that the resultant required extra shm thickness is within an available range. It is possible to end up with a too thick shim being required depending on you current valve installation and the new base circle but this is unlikely if the rest of the valve train is within normal standard assembly dimension tolerances

The use of sprint cams, a tubular exhaust header and sprint 33mm chokes and jets and timing curve produces most of the benefit and I would not bother doing the valves themselves until the next rebuild is required. At which time doing the big valve sized inlets costs the same as the standard size and will reduce the potential need to replace the inlet seats as the bigger diameter means the valves can be seated at the correct height rather than requiring a deeper cut

cheers - this was actually my first twin cam development project i did on my Elan a few months after i bought it and about 35 years ago
Rohan

[nebogipfel]

That's a very comprehensive reply, thanks Rohan.

I was concerned about the resultant shim thickness required and also if the grinding process would cause any issues with the strength of the shaft?

I assume the person doing the reprofiling would be able to advise me of any implications regarding shim sizes?

Best Regards.

[nebogipfel]

A relevent thread from May 2009. Well worth revisiting:

elan-plus-f13/sprint-cams-t18318.html

Thanks Richard, I'll have a look

[Jeff@Jae]

What Rohan said plus......
The "Big" valves have the advantages in fitting as Rohan described and they are actually a better head shape for flow. So, no need to change if you don't want to but they are a better valve to use beyond being just a bit larger.
Spend the time to properly time the cams to the correct lobe centers (using offset dowels) and not just rely on the marks. This step alone can result in huge gains in power and drive-ability if the original cams are out as much as I've seen in some cases in addition to the cam lobe centers moving a bit more on the reprofile process. Very important step in the build process of any Twin Cam and especially with reground cams.
Have your distributor checked out and recurved to match the latest spec. in Miles Wilkins book.
Rejet the Webers or Dell Ortos to Sprint specification.