Renault 697-04 pistons and compression

[lotuseater]

Does anyone know the performance difference between the original Lotus crowned pistons which gave a higher compression than the Renault 16 flat topped pistons?

Mine has been fitted with the Renault variants - they run well and rev freely. Engine currently in bits as I had a bit of mayo in the cap so I checked compression for suspected Head Gasket Failure -  I've got low compression on No 4 cylinder (165psi on 1,2 & 3 but only 112psi on No 4). As yet, I have found no reason for this - gasket contact looks good to both head and block, valve seats slightly pitted, but not leaking with a water test (inverted head and filled with water). Nothing else looks out of order.

Is there a source for the crowned pistons and is it worth it? Current pistons & liners look to be in very good condition.

[TurboFource]

I believe the surface tension of water is to high to test for valve seat leakage, usually a solvent is used.

[lotuseater]

Thank you...will try thinners or panel wipe.

[BDA]

It's too late now but one thing you could have done before you took your engine apart is a leakdown test. That would have told you where the leaks are.

[MRN I J]

paraffin is commonly used

[Rosco5000]

From a power output standpoint the R16 is a 66hp 1470cc engine and the Lotus high compression version is 82hp. 

From Wikipedia so take it for what is worth "For Lotus' use, the Renault engine was given a number of key improvements, including a higher compression ratio (10.25 instead of 8.6), larger inlet valves, revised valve timings, dual valve springs and a twin-barrel carburettor. These changes lifted the engine's power by 23% from 63 hp (47 kW) at 5,000 rpm to 82 hp (61 kW) at 6,000 rpm. For US export, a de-tuned 1,565 cc (1.6 L) version with a maximum output of 80 hp (60 kW) at 6,000 rpm was fitted.[5][6]" 

There are a couple of differences besides high compression.  My S2 came with a standard Renault lump installed.  I never drove it but the previous owner said it was noticeably slower (he did the swap when the Lotus engine had an issue).  With all this said you probably loose as much as 5-10hp in the renault engine.  Compression increases in my other engines of similar size are noticeable. 

I do believe Banks would have pistons at times probably the best starting point to look, otherwise you might need to order custom forged pistons.

R

[SilverBeast]

Start Pedant mode

(82-63) ÷ 63 = 0.301  - a 30.1% increase from 63 to 82 BHP.

End pedant mode

I realise this is covered by the "from Wikepedia" caveat. 

[GavinT]

"Renault 16 Shop" list piston and liner sets for the Lotus 1470cc 697 engine (as well as the Lotus 821 engine).

https://www.renault16shop.com/Lotus-Europe

[1970S2]

I just bought Wiseco domed 10:5 to one pistons with the 21mm wrist pin free floating , the rings are steel, not cast, nice and thin ,  cylinders rebored to 78 mm ,I need to rework the head to accommodate  the dome, I'm ordering a hemi-cutter tool to do this job, will post pictures of the piston soon.....

[lotuseater]

thanks for the feedback. I seem to have a proper 697-04 'lotus' version of the engine with the correct larger sized valves and double springs (presumably the Lotus cam). The only thing that seems to have been de-spec'd are the pistons, so I might have more than the original Renault 63BHP, but probably not the full 82BHP.  Hence, the only thing that would be changing is the compression. I'm just wondering whether I will notice the difference and hence is it worth the cost of new pistons/liners or just a marginal improvement. Someone also mentioned that they had higher octane fuel back then - the best now, in the UK is super unleaded of 97Octane I believe.

I do have the original Lotus fitted, Solex carb, but just couldn't get it running properly, so gave in, according to common opinion, and bought the single weber. I'm not chasing big HP gains by looking at crossflow heads, branch manifolds, double webers etc, just interested in it being as original as possible, yet good. fun.

[GavinT]

Good to hear the rest of the engine is kosher.
A change of pistons/liners would invariable lead to a full rebuild incorporating all the parts that would be recommended as part of that process anyway.

Piston/ liner kit, main bearings, big end bearings, cam chain, tensioner, clutch, gasket set, seals, oil pump . . on and on it goes.
Shipwrights' disease?

What's the difference likely to be? . . . maybe 10HP?
Personally, I wouldn't worry about it. The pure fun and enjoyment derived from a Europa isn't dictated by 10HP IMHO.



Actually, Shipwrights' disease deserves a dedicated thread of its own . . . hint, hint.
I reckon that'd be hilarious and a timely warning to all. 

[1970S2]

picture of my new 10.5 :1  piston, 78mm with the 21mm wrist pin, this is a forged piston with steel rings, you can see where I have to remove some material in the head, ( its scribed out ) just waiting for  the special Hemi-cut cutter to come in from California , I have it mocked up on the mill to get it ready for the operation , I need to plunge down 2mm to make clearance for the piston on the head, should look nice when its done, with the engine combination I am using , it should make 135HP , it includes HP grind on the camshaft, lightened flywheel, (my next  project ) high volume oil pump, all new bearings and timing chain with new tensioner, upgraded Gordini rods, twin 40mm side drafts, and a Alpine header........lots of work to do this winter....

[1970S2]

new HEMI CUTTER came in , just have to wait till i get some time to machine the head

[Richard48Y]

Hmm, my pistons look very similar but appear to be German made.
Head has been modified for clearance, looks like it was done old-school, by hand.