MGB & GT Forum

Victoria British and my machine shops supplier list 8.50 CR pistons for 18V motors. Does anyone have any details on these as far as dish volume, manufacturer, etc? I'm thinking they are probably replacements for the OE large dish, low compression (8.0) pistons on the later cars but want to be sure when I talk to my machinist. Or do they actually hit 8.5 with the 38cc combustion chamber heads? I definitely do not want to go back to the original 8.0 compression.

Thanks

The two most common piston offerings for the 18V is the County 8.8 to 1 piston and the AE/Nural 8.8 to 1 piston, I seriously doubt that Long Motor Co./Victoria British carries anything different from the rest of the world's suppliers. As for the 8.5 CR claim, never heard of that, and I think if existed I would have heard of it, this is what I do. I doubt anyone at LMC is smart enough on anything MG to even know, they seem to be experts of nothing I dealt with them to their highest level, yet to be impressed by anyone there. The 8.8 to 1 piston offerings for the 18V actually nets 9.2-9.6 to 1 depending on bore size, we've already heavily documented that here, you can search and see it here.

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Hap Waldrop
Acme Speed Shop
864-370-3000
Website: www.acmespeedshop.com
hapwaldrop@acmespeedshop.com

Here is the info from VB catalog

Agree with Hap. I know of no supplier offering an 8.5:1 piston for our engines. The two configurations commonly offered for our engines are the low compression pistons, which have a deep dish 3/8 deep at the center measuring about 16 cc's, and providing 8.0:1 compression using a late cylinder head with a combustion chamber volume of 38cc's. This would include the 12H2923 "big-valve" head from 72-74, and the CAM1106 head used on all the later heads.

The other piston configuration most often sold for our engines is the shallow dish piston. This has a dish of about 3/16 in the center, measuring about 6 cc's and, as Hap points out, provides a highly-desirable compression ratio of 9.2-9.6 or so, depending on the bore and also on how much material is removed from the head and block surfaces.

I would be very surprised if there was a regular production piston out there that differs from the two described above. The simplest way to distinguish between them would be ask to the supplier to measure the depth of the dish at the center of the piston...

Dick

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Errabundi Saepe, Semper Certi
(Often wrong, but always certain)

Just call VB and ask to talk with someone in Tech Service...

Dick

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Errabundi Saepe, Semper Certi
(Often wrong, but always certain)

I'm wondering if it was just a typo, and they meant to print 8.00 to 1.

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Friends talking around a fire is the history of mankind.

The piston shown is a standard bore, doubt your old tired engine is going to run stock bore. 3.159 pistons

You can get parts at discount from Chris Roop MGE forum member local to you
or BPNW also local and they both know of what they sell.

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I've been talking to Hap and others about parts so I was never planning to order from VB. My machine shop is trying to sell me on their supplier (I think it's ITC or IMT) and their catalog lists the same 8.50 pistons. I am meeting with him tomorrow and want to point out that his vendor may be selling the same crap as VB. The owner even specifically warned me about his bad experiences with VB in the past. Shop has a fantastic reputation and has experience with british cars but based on this, I am insisting on the customer supplying the parts.

One more time...thank goodness for the collective wisdom on this site and out there in the MG world.

Hehe, I've been waiting 11 years now for the tech dept. to call me back

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Hap Waldrop
Acme Speed Shop
864-370-3000
Website: www.acmespeedshop.com
hapwaldrop@acmespeedshop.com

It is interesting that they show a distinct part number for the 8.5:1 piston. It would be worth trying to get someone at VB to tell you who manufactures them and see if you can get the actual manufacturer's part number.

One thing that has always puzzled me is that, in Europe, the 18V engine came with a 9.0:1 compression ratio. Did such pistons ever exist? Or were they just using the 18Gx 8.8:1 pistons which yield around 9.2:1 on the 18V head?

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Terry Ingoldsby
terry.ingoldsby@DCExperts.com

Wherever you buy them, go with the AE or County pistons so you get a known product regardless of how it is advertised. My Plan B parts are from BPNW.