Upping the compression ratio with light weight pistons

Post Sat Jul 22, 2006 8:28 pm

Good work Andy! i can smell the oil from here

A quick lesson...

25.4mm to a inch, so 1mm divided by 25.4 = 0.03937 inches. So yes 1mm is approx 0.04"

PS i use the Google toolbar spell checker...

Post Sat Jul 22, 2006 10:35 pm

Hi,Andy not been on here for quite awhile what with the football and Jan has been in hospital.Glad to see your are getting somewhere,what I have done in the past is used play doh it creats a good mould.Took the engine out of mine,looks like I'm abit behind you,but rebuilding it but before I start it I'm going to finish the underneath of the car first.I do believe that the Alpina heads were different from the standard E34.bigger valves and higher lift cam.And if it's a Alpina block they should be light weight pistons fitted as standard and the light weight fly wheel, but someone please correct me if I'm wrong, but that's whats on mine. Pity I'm not ready to do mine or else I could send you pics of what it looks like.But I'm very interested in what you are doing,good luck if you get stuck or need any help PM anytime.

Post Sat Jul 22, 2006 10:53 pm

Probably a bit late but if you are working to an exact squish clearance you will need to know the head gasket thickness, an engine building company should be able to get hold of a few different thicknesses

Post Sun Jul 23, 2006 4:20 pm

those bearings look not so good!

great pics mate keep em coming

Post Sun Jul 23, 2006 10:40 pm

RJB6 wrote:Hi,Andy not been on here for quite awhile what with the football and Jan has been in hospital.Glad to see your are getting somewhere,what I have done in the past is used play doh it creats a good mould.Took the engine out of mine,looks like I'm abit behind you,but rebuilding it but before I start it I'm going to finish the underneath of the car first.I do believe that the Alpina heads were different from the standard E34.bigger valves and higher lift cam.And if it's a Alpina block they should be light weight pistons fitted as standard and the light weight fly wheel, but someone please correct me if I'm wrong, but that's whats on mine. Pity I'm not ready to do mine or else I could send you pics of what it looks like.But I'm very interested in what you are doing,good luck if you get stuck or need any help PM anytime.

Hi Roy, i hope you are well and Jan is getting better ?

Looks like your M30 is based on the E28 generation M30 so you will probobly have a single mass fly wheel rather than the E34/2 dual mass fly wheel.

Your right about the heads being differant and having Mahle light weight pistons, it's because of the pistons sticking further out than the normal pistons that i'm having to reshape the squish band on my head.

Theres some pictures of the pistons on the first page of this thread i think ?

Acording to the previous owner who has had the sump off it's suposed to have piston oil squirters like the M106 from the 745. As well as the pistons it has stronger/lighter M5 con rods which cope with higher RPM's better.

Stonesie, i have an old HG that i've measured, i guess an old HG has compressed already if it's used ?

The ETK shows two HGs of differant thickness, 1.72mm and 2.07mm which i think is the compressed thickness as the new HG i've got is between 1.9mm and 2.0mm.

But it's handy to know that there might be some other thickness's available from engine builders as it's going to be very tricky to get every thing the same when you are looking at getting things with in +/- 0.1mm