Hello. I'm putting the 117 5.6-litre V8 from a 1989 560SEL in my 1971 280SE (108). The 108 has LPG injection and I plan to run the 560 engine on LPG too. In order to take advantage of the high octane of gas, I want to raise the CR as much as possible. Does anyone know what the maximum amount of material is that I can skim off the heads before I run the risk of valves hitting pistons? What's the official Merc figure? And does anyone know how much this will throw the cam timing by?

One last thing - what's the maximum warpage allowed on a 560 head? Mine are currently 3thou out over their length. Is this accepatable according to the manual? I just want to know in case there isn't scope for getting much of a CR rise through head skimming. If that's the case I won't bother – if 3thou is okay.

Thanks in advance for your suggestions.

Whereabouts are you located? If you have a 'euro' engine, ie the option 822 300hp engine, then its already got quite a high compression, and I wouldnt really take it any higher.
I have one of the 5.6 option 822 engines in my 500SEL running on LPG, and its great!

If you really want to take the compression as high as it will go, I can look up the specs later when I get home and let you know how much you can skim off.

Valve timing is quite easy to adjust and from memory offers upto 12' of adjustment in either direction, by installation of offset keys on the cam sprockets.

Hi. I'm in the UK so the engine is the 300 brake spec unit. Isn't the CR about 9.5:1? If it is it could do with going up so that I can get the best possible efficiency from LPG.

If you could look up the specs I'd very much appreciate it. What are your thoughts on the 3thou runnout?

Cheers

Will Holman

Off the top of my head, I thought the compression was more like 10.1:1 on the 300hp unit.
I'll look up both specs for you later, unless someone else can chime in first!

Cheers.

Thanks. Much appreciated.

117.968 220Kw 300hp 10:1 compression
You are allowed 0.08mm unevenness through the length of the mating surface, but none in the width. (So your heads are just about acceptable, assuming the block is perfect)
Dimension H cannot be less than 59.55
Total material machined from both head and block cannot be more than 0.5mm
Valve seats should be machined by the same amount as the material removed from the head.

Dont forget to helicoil the head bolt openings in the block using the proper jig, and use new head bolts.

Also, its worth changing all of the intake rubber, especially the large boot under the fuel distributor and the injection grommets. Vacuum leaks effect engine performance massively on LPG (ask me how I know!)

Hope this is of help!

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That's brilliant - thanks. In which case I shall leave them as is and bolt them back on. Are the head bolts reusable?

I just edited for you!

Oh yeah.... and dont get the new bolts from Eurocarparts, they are actually cheaper from the main stealer!

Thanks. I've already got new rubbers for the plenum to manifold joints. I'll order some head bolts though. Thanks for your help. I've been on three Merc forums prior to this one and they were all useless. Looks like I finally found the decent one.

I'll be using LPG injection, although I'm not sure which make yet. The 280SE has Romano injectors but I'm getting suspicious of their reliability so might try some others.

Will.

No Problem!

What are you doing about the KE jetronic computer and EZL? I ditched both in my 5.6 transplant, and went with the older K jetronic and old style distributor. I think it simplified the installation massively. I have a spare K jet fuel distributor if you need one.

Cheers,
Ben.

I'm not sure yet Ben. As I don't plan to run the car on petrol at all unless I can't get gas, it seems a real pain to set it all up. However, I want to get it running on petrol so I can drive it to the rolling road for mapping of the gas system. I've removed everything I need (I think) to get it running but the wiring looks like a nightmare, despite it being mechanical injection. My choices are to wire it all up and get it running or to ditch the K-jet completely (thereby losing the metering head, which looks like a hindrance to airflow) fit EFi injectors and have it mapped to run EFi and gas Fi.

Both options seem like a ballache!

Will.

If you go with the K jet from an earlier car, and not the KE jet that the 560 comes with, then you can simplify the wiring greatly. Just the fuel pump and the distributor need sorting. If you go with the earlier style vacuum advance distributor, then you just need to wire in the ignition module, which is a couple of wires for power, and one to drive the rev-counter.
You could get the idle computer, but just to get it going, you dont need it. You'll just get a high idle without it.

Cheers.

So which parts do I need to convert to the earlier setup, Ben? The metering head, dizzy and what electronics?

And which car are you putting this in, Ben? Or have you done it? Is it up and running?
Will.