60th anniversary of the Mk2

[JCS]

“For anyone taking the head off and looking at your pistons it is actually very easy to see the difference between 7:1, 8:1 and 9:1 ration pistons”.

I am afraid that statement can well be in error. In respect of piston head shapes they will indicate NOTHING if the block has been “decked” or the cylinder head re-faced. As soon as you reface either the block or the cylinder head you are altering the compression ratio and cylinder pressures. Nearly all of these engines have had components refaced and it is sensible to establish the situation before proceeding to remove a head, if the engine detail is unknown.

The piston heights are only shown in the workshop manual to indicate the compression ratio’s on an engine with STANDARD standing heights that is a standard block height, standard head depth and standard bores. This produces a certain combustion chamber volume, which as I say is reduced (compression ratio increased) once block height or head depth is reduced by re-facing, or in fact the engine is re-bored.

[cass3958]

Pistons.JPG

A picture paints a thousand words. Thank you Glyn.

I agree with you Norman that it is nice to know what your compression is before you work on the engine and what you have after. I was just pointing out the difference between the pistons in relation to the compression ratios indicated by your engine number. The last digit of which reads either 7, 8 or 9 indicating which pistons you have fitted to your engine from factory. I had 8:1 ratio pistons and my engine number is 7D10211-8 but when I rebuilt my engine I went over to 9:1 pistons.

[Glyn Ruck]

Yes ~ Orlando & a number of us take into consideration our actual post renovation CR for timing settings, fuel octane etc. Have not had to consider different thickness gaskets.

[JCS]

Nigel

A couple of points………..once you have the cylinder head and bonnet removed the access to fit an extra camshaft oil feed is very good. Considering that manifolds and carburettors are also off the engine at that stage an extra oil feed is easy to achieve as you will have already removed the banjo bolts from the cylinder head. You could find it a worthwhile improvement.

I have noticed that in many cases replacement head nuts do not have sufficient FULL threaded depth, although the maximum internal depth may in fact be deeper than the original nuts. As you are no doubt aware this can lead to bottoming out between nut and stud resulting in a false indication that the nuts are torqued down.

Yes, I would agree, it is not a good idea to remove and replace any head bolt/nut without changing the gasket, particularly if the gasket is a mono steel type.

As a matter of interest…..Does your engine have factory type inlet valve oil seals?

[NigelW]

Thanks for that JCS, I'll check the head nuts very carefully against the originals - not seen that before. I've never had an oil problem with the cams as the racing pump and associated large bore oil pipes gives me 70psi pressure on start up from cold when most of the engine wear takes place. Yes I'm using factory spec oil seals on the inlets, is there anything better? I wasn't planning to strip the head down as it's done less than 10k miles since the last rebuild, everything appears ok but as you know plans change! Nearly ready to lift the head off at the moment- coolant drained, bonnet off, carbs off, just a few pipes to do and exhaust to disconnect. I don't have a full day to work on it today due to domestic stuff but see how far I get.

[Glyn Ruck]

My engine rebuilder mentioned the potential for domed nuts bottoming on the studs. We used rechromed originals with the threads blanked from the chroming process by a silicone sealer plug.

Banjo washers.
http://www.jagstyperegister.com/forum_n ... f=17&t=166

I have extremely healthy oil pressure & good flow to the cams.

[NigelW]

Didn't get the time to lift the head off today but after the comments on the thread depth on the domed nuts it got me worried so checked them and they are identical to OEM items with enough thread to accommodate the studs.

[Orlando St.R]

Not sure where else to post these couple of pix and didn't want to start a new thread. Herewith a pic of Norman's S-type at the 20-49 Motor Club meeting last night at Barrowden, Rutland, plus another pic from the opposite direction. It's difficult to imagine a more idyllic location to hang around, have a beer and a burger, and admire some amazing machinery.

WP_20190606_19_09_45_Rich.jpg (3.24 MiB) Viewed 2749 times

WP_20190606_19_11_15_Rich.jpg (3.8 MiB) Viewed 2749 times

[JCS]

Ah Roland, nice picture of the Red un !

Thanks

Norman