New S1B owner

[jbcollier]

The amazing thing is that you were prepared to machine your pistons based on figures pulled off the internet.

[GavinT]

I think I found the weird engine discrepancy!

The place I was pulling data from, Dave's page here uses a 697-02 engine to compare to the Lotus tuned 697-04, not the -01 found in the standard R16L. The -02 must be the low compression version of the engine for certain export markets, as it has a 7.6:1 compression ratio rather than the 8.6:1.

Ah, right . . I should have twigged.

The early Renault16's are probably better referred to by their Vehicle Type which is R1150 and came with either the 697-01 (High Compression) 697-02 (Low Compression).

The language Renault used was for markets with "poor fuel". There's many variations on the R1150 theme and I'm not sure anyone has it all figured out.

Here in Oz, we had a Renault assembly line for the CKD cars and our versions were fitted with modified suspension for our "poor roads". Back then this was a common practice for imported cars which sometimes suffered badly in our outback.

[314159td]

Starting to gut the engine...further evidence that somebody was in here with no idea what they were doing. Weirdly, I wasn't getting an obvious drip from this one. The power of corrosion as a sealing mechanism 

Main bearing caps are all sorts of messed up as well, the number stamps are in a backwards order.

[jbcollier]

#1 cylinder is by the flywheel.

[314159td]

I'm aware, though they're messed up in a way that is agnostic to the correct piston numbering scheme. Rod cap order is correct, main caps seem backwards, plus something else maybe.

The manual implies the rods come marked, and the main bearing caps must be marked by the reader, so maybe the latter were simply marked incorrectly at some point? But the stamp font is identical on everything, so that seems unlikely.

I've recorded their current orientation regardless, hopefully that hasn't caused issues. At first glance, the crank journals appear unharmed.

[314159td]

Back to compression ratio discussions...I happened across something that gives me an idea. While thicker head gaskets don't seem to be offered (I might not be French enough to find them), this site sells a 0.5mm "Cylinder head copper shim" for the same engine family, directed at the A110 and R12.

Assuming nothing lost in translation, that implies someone has figured out how to make a simple head shim work with the rubber oil sealing gasket. Maybe the answer is just RTV silicone, it seems solvable regardless with low crankcase pressure.
Given the more complex interface on the block side, I think I would put the normal head gasket on the block and a shim on top of that, with the standard copper spray some people seem to swear by.

I would need a shim of ~0.8 to 1.1mm, slightly thicker than what's usually offered (0.020 in or 0.5mm seems to be the standard, including some newer engines).
Lotus's shop manual specifies a maximum of 0.3mm removal, stricter than I've seen elsewhere, implying their camshaft modifications further eat into the margin. That's what sent me on this investigation while examining camshaft geometry and my 1.07mm shaved head.

Manufacturing isn't an issue, but I need to figure out if either steel or copper makes more sense. I feel like annealed copper is a "safer" choice for sealing, and there aren't any super close bore spacings that sometimes blow out weak gaskets, like on the classic Minis. Most concerned about water leaks honestly.
I have some backup ideas for a custom, thicker rubber oil seal as well, or maybe extend the shim to increase the thickness of everything on the head, not just the head gasket area.

Thoughts? Murmurs of other people doing this? I know some manufacturers had an OEM shim kit like this in the 60s to lower compression, but Renault seems to have addressed that though dedicated engine variants, so I don't expect to find an example in their manuals.
It seems like this solves more problems than machining down the pistons, and is fully reversible without removing the engine in case it fails. Happy to put money in someone's pocket for a head and then rebuilding it if I absolutely have to (I see you Richard48Y, and those alloy rims).

If I just slapped the head on with domed pistons, it would be 11.1 CR, which is probably fine going by JB's comment earlier in the topic, but if I wore a cam lobe flat...the engine is coming out, or a hole saw is going into the firewall.

[314159td]

I think I finally a set of alloy wheels that look right, going for a 70s/80s retrofuture aesthetic. Came off a Spitfire, they should sit about 1/2" further out than the originals - similar to the later Europa alloy wheels. Apparently made locally, which is always neat. 

[BDA]

Those are nice!

[Richard48Y]

I have two of those.
Had four until a wheel restoration shop lost two.