6.9 and 6.3 cylinder heads - a bit off topic

[grant v]

Can anyone tell me whether I would be able to fit 6.3 cylinder heads to a 6.9 engine block?

 

[s class]

Now why would you want to?

 

[Styria]

Hi GrantV,

The answer, in short, is no - they cannot be swapped for any number of reasons. Whilst the 6.9 may have been referred to as a logical successor to the 6.3 at the time of its introduction, the two models are in fact like chalk and cheese in just about every aspect - they may as well have come from different manufacturers.

There are even variations between high compression and emission controlled heads. The right hand head has been machined with a channel and fitting to accept the pipe connection for the anti smog pump. Engine blocks are different as well, with the three intermediate main bearing caps being four bolted . Regards, Styria

 

[grant v]

Thanks, Styria, that's exactly what i wanted know.
Ryan, I'm planning to build a replica of the 300SEL 6.8 Racer to go racing with, and I thought that maybe it would be easier to use a 6.9 block with the 6.3 heads, than to bore and stroke the 6.3 block to 6.8 liters.

 

[Styria]

Hi GrantV, it would be easy enough to obtain the extra 500cc - just a simple matter of increasing the bore by 5 millimetres. Where things could turn sour is when you have to purchse new pistons - for instance, I gather that a set of 6.9's are worth a fortune. Don't know how one would overcome that. Regards Styria

 

[grant v]

Styria,

Is there enough meat to be able to bore it out an extra 5mm? Any idea what a set of 6.9 pistons would cost? A fortune might just be relative here.

 

[Styria]

Hi GrantV,

Without looking it up, I think the difference in bore diameter is 4mm, and not 5mm. As I have previously said, the press blurb at the time of the launch mainly referred to the larger bore size, and they forgot to mention all the other changes. The 6.9 block's skirt has been extended to below the centre line of the crankshaft in the interests of greater strength, but for all I know that may only be , say 2mm, but it could be 15 - you know what I mean ?

Say, if you were to machine the bore by 4mms, the idea would then be to use 6.9 pistons. So, you could buy new - and you would find that they would have to come from Germany probably at about $US 1200.00 per piston, and even Companies like Autohaus Arizona if they don't have access to aftermarket parts, are quite close in their pricing structure to the OEM price. Forget Australia - our prices are sky high.

Next, you could then also consider used 6.9 pistons, but you'd still have to purchase new rings. There are some American rings that could be cross referenced, except for one ring where the 6.9 piston has a wider groove and, as far as I know, nothing else will fit, so you're back to original and the higher pricing structure. In addition, you may have to look at conrods - is there any diffrence between the 6.3 and 6.9 items ? At what point are the gudgeon pins situated ? Until you have comparable parts side by side, you may well be subject to a lot of guesswork.

Your last option is to fit a 6.9 engine to the 109 chassis car. It's been done with 107's, so I am sure that with money and the right people the job could be done. There is a post in "Topklasse" that refers to just such a conversion. Regards Styria

 

[SEL_69L]

Interestingly, I have heard of a situation where some rings from a 454 big block were shaved at their ends and they fit in the wider groove. The piston weight with the different rings is only slight greater. Might be worth investigating further.

 

[BenzBoy]

Or you could try http://www.jp.com.au/
There are very few, if any, pistons that they can't make.
Regards,
Benz-Boy

 

[John S]

That's a great site; it's good to have a specialised business like this in Australia. However I am surprised that the photo they show as the reaming process is seemingly being done by hand, looks more like drilling the oil relief holes - they know what they are doing, so where / why am I being misled by the photo?

 

[BenzBoy]

That's a great site; it's good to have a specialised business like this in Australia. However I am surprised that the photo they show as the reaming process is seemingly being done by hand, looks more like drilling the oil relief holes - they know what they are doing, so where / why am I being misled by the photo?

I guesthat little problem is coused by the fact that it is a home-made website without all the glitz and glam of a professional one. Thus mistakes in the website are of little consequence to them....I guess.
They are well-known around the world as manufacturers of high quality pistons for a range of vintage cars and apparently they are quite happy to make any piston etc at a reasonable price.
Interestingly though, 2010 is the year I will rebuild the PII engine and my mechanic is planning to cast and machine the new pistons himdelf rather than use the JP ones. Having seen some of his Ghost pistons side by side with the JP ones I can understand how much more care a professional can take when he WANTS to do the job himself.
Regards,
Benz-Boy