Adrian,
some were OK, but some were not, as evidenced by the number of engines which have had replacement piston and barrels fitted long before they should have needed them.

Don't forget that I've probably spent far too much time fixing them after others have broken them...
As recently as this year's Registers' event, I was asked to adjust the timing on a car which had just had new barrels and pistons fitted at a cost of around £600.
If I recall correctly, the timing still had at least 3 teeth too much advance, so those new parts could easily have had a very short life if the owner hadn't realised what was going on and driven to Registers' on a very light throttle.

Relevant page from a 1987 2CV owner's handbook here, which suggests that Citroen themselves might have had second thoughts...
< http://www.flickr.com/photos/30132857@N ... /lightbox/ >

ken

( Engines do run both leaner and hotter on unleaded fuel than on the leaded equivalent, so the usual advice about changes in jetting, spark plug heat range, valve clearances and accuracy of timing adjustment apply. )

WTF? £600 for a set of pistons? I'm assuming they were some sort of highly tuned racy jobs then?

Hmm. I thought the actual CitUK recommendation was 2* - then 95 unleaded without adjustment.



As you say - "after others _have broken_ them..."



^ fine example. Doesn't say anything about the actual ability of the engine - set up to spec - to run on 95 or lower.

I know the Germans had 7.9:1 pistons for 91RON undeaded, though.

Adrian,
isn't it all about the margin of safety?
Switching to unleaded reduced the acceptable margin of error when setting the ignition timing and those folk who cannot, or will not, adopt a more accurate method of setting the timing than the original often suffer the consequences.

Of course, installing a fully electronic unit removes most of the small amount of skill needed to set up points, but not all of it...

The example given was solely to illustrate that there are still 'specialists' around who have not grasped the importance of setting the timing accurately.

@ Russell,
I'd guess that £600 covered installation of the new pistons and barrels, but didn't seem to cover addressing the reason they were needed in the first place.

ken

...finding their backside with both hands, a torch and an illustrated guide to the differences from an elbow.

I have driven my DS 21 on unleaded for 10 years, no problem. Have also driven my 2CV on unleaded 95 the last three years with no problem that I know of. I have electronic ignition, and did a check of the el.ignition's function during revving, as described by Ken on his photos, with the white markings on the teeth's checked with a strobe. It was spot on all the way.

95 is cheaper than 98, so I prefer that. As other's have said, they run 9:1 with 95 oct.and have no problem. Can I assume that, if everything is set up right, as it should anyway, it will work just fine with 9:1 and 95oct?


Ken, if this is things that deviate from original specs, you care to give a "quick" list of these things? Would be nice

Before modifying anything, remember that AK/ACA and Ami 8 are running with 9.0:1 pistons without problems. These cars do not fail more due to higher ratio.
Sorry I'm a purist, keep it original

EirikJ,
as requested...

Richen the mixture by increasing the primary petrol jet by 2 steps ( 102.5 to 107.5 for normal induction on 18-26 versions of the 26/35 carb, or 110 on 'blown' induction set ups)
Increase primary petrol jet from 120 to 122.50 or 125 on older, 21-24 versions of the 26/35 carbs.

Fit 'colder' plugs than originally specified, NGK B7HS for steady drivers, B8HS for those who like to keep the pedal hard down.

Inlet valve clearance 0.2mm, exhaust valves at 0.25mm.

Maximum ignition advance between 33 & 35 degrees for 8.5:1 engines on 95 octane fuel, probably several degrees less for 9.0:1 engines.

The overriding factor is that there must be _no_ pinking and since this is dependent upon engine condition, driving style, ambient temperature, altitude and so on, pay attention to what your engine is telling you...

ken.

Viking,
didn't AK and ACA have 8.5:1 C.R. originally?

ken