4.2 Pistons and rings - any recommendations

[Curtis Bay]

As part of my engine rebuild I am having to replace my pistons and rings. The engine is a 1965 4.2 from a UK FHC (manual). This has (or rather will be) fully dynamically balanced and totally rebuilt with new bearings, seals etc and will be fitted with the orginal, but fullly refurbished, triple SU's. The head will be given a little port and polish but nothing drastic and it will have an E Type fabs long branch exhaust manifold. Apart from the minor alterations above it is a standard specification.

Has anyone got any experience or recommendations on the type of pistons I should use or avoid? My plan is to have a very smooth and reliable engine that can be used for normal road use and that will give years of service. I am not averse to upgrading the internals if it makes sense to do it whilst the engine in in bits but I do not want to get carried away spending a fortune on perfomance I will never use.

Any advice would be appreciated

[christopher storey]

I used AE pistons last year but they are now difficult to get hold of and are very expensive, IIRC ? 470 for the set. I have heard good reports of JE pistons from Australia, but order well before you need them because they take about 6 weeks ( I think) from order to UK delivery

If I can offer one bit of advice : use 8:1 pistons, because by the time the head and block have needed decking ( or you find they have been decked before) the CR gets out of hand with 9:1

[Nick]

+0.020" AE pistons went into my 4.2 when E-type UK rebuilt it (part no. 21379V1).

I haven't had pre-detonation problems with these 9:1 pistons after the head and block were cleaned up. You need to remove quite a lot of metal to make an appreciable change to the CR. I do run on super-unleaded though.

Nick L.

[JEP41]

Hi Curtis,

I have a MK2 3.8 which I rebuilt some years ago now with Cosworth Pistons and a Compression ratio set to 9.5:1. This engine has been brilliant with no detonation. Very little skimming is necessary the compression is set by the piston its-self and should be specified when ordering your pistons. It is a must to check during the build though and easy to adjust with moderm composite gaskets such as comtec. When I built my e-type engine also a 3.8 litre, Vernolia pistons were all the rage so I used these expensive but again they have been excellent. These require much bigger bore clearances than the Cosworths so until the engine is warned up appear noisy. Bearing in mind fuel quality again I stuck with 9.5:1 compression and have experienced no detonation problems with this engine which runs on webbers either. My current engine which I am building at present for my C-Type. I am using JE pistons again because they seem to be all the rage at present. However I have no personnel experience of JE yet? This engine is also a 3.8 litre and I requested 10:1 compression for these JE pistons when I ordered them as we have much better control of timing these days using the 123 distributor etc. However if I change my mind, with the variety of head gasket thichness's available it is a simple job to calculate the compression ratio and re-adjust using a composite head gasket. Note when rebuilding an XK engine the machining of the head and block should in my opinion be kept to an absolute minimum required to obtain true flat surfaces not to adjust compression ratio. Compression ratio should be set by the piston and the required ratio stipulated when ordering the piston and definateley double check the compression ratio during assembly of the engine. :D

[Curtis Bay]

Thanks for the information - has anyone had any experience of the pistons from Classic Jaguar in the USA?