VG 3260

[Ian Grace]

Incidentally I disagree with Ian’s advice to take metal off the head to improve the performance!

Hi Ken,

Your saloon certainly seems to go well on the road. Are you running an original Minor cam as well? The standard Minor was rated at 20 bhp I believe, and the M Type was 27 bhp - a considerable increase, but some of this must also have been due to the larger carb. And the M's performance on the road would also have been considerably helped by its lighter weight. (I'm amazed how heavy the Semi-sports body is - the ash frame is built like a tank by comparison to the M! More like a Quarter Sports than a Semi Sports!).

I must admit that I have always raised the comp to M Type spec on all my OHC Minors, and fitted a 12/12 cam, and the resulting performance has been good. What I have not done, I don't think, is run a 12/12 cam in an unskimmed head. Scope for some scientific research here? Minor comp/Minor cam, Minor comp/M cam, M comp/Minor cam, M comp/M cam, and the same again with an M carb/manifold!

Footnote on cams - I don't think standard Minor cams are obtainable - so it's Hobson's choice if your cam is worn - unless you go to the expense of reprifiling.

[DF9053]

The M type's original power output has been something that has puzzled me of late. The Minor was rated at 20bhp and the early M types were always written up as 20bhp as well but they had a higher compression ratio and a larger carb/manifold. So surely they must have had a greater bhp than a Minor.

The M type became rated at 27bhp when the 12/12 cam became available didn't they?

This cam gives longer inlet valve opening and must mean more fuel mix to explode - bigger bang more power all logical. But of course the valve timing is very dependant on the condition and shape of the rockers - Minor/M type rockers are not available new.

I am sure the lighter body helps but the coachbuilt saloons were only 3cwt heavier so the semi sports and fabric saloons can't have been that far off can they? Clearly four or five up in a Minor will sap its power!

It may well be worth rasing the compression ratio - it will improve power a little but bear in mind you can't put metal back once it has been taken off! It will also run hotter and be more prone to pre-ignition. I would have thought that a well used Minor would have had its head skimmed a couple of times in its life so there are probably examples out there to use in you experiement Ian.

Sorry this is a bit of a ramble but just thoughts as they came inot my head,

Cheers
Jeremy

[Ian Grace]

In his article about his M Type for this year's Yearbook, David Roscoe recounts a trip to the pub in the car - six up! I wonder what the performance was like on that run! I'll leave it to you to read how they were all seated!

As for not being able to put metal back, one could resort to the old trick of fitting two head gaskets!

Yes, I think it was the post 12/12-cammed M's that 27 bhp was claimed for. I'd be interested to know if it was at this point that the comp ratio was upped as well from standard Minor. I think they all had the bigger carb and manifold, from M251.

Dynamometer anyone?

[mike houston]

Thanks to Ken, Jeremy and of course Ian for your thoughts. The head has been skimmed to 3.5" so there is no going back on that! Now there doesn't seem to be a lot of point in running the standard cam, even though it seems to have little wear, so I guess I'll be going for the 12/12 cam. Incidentally I was particularly struck by the idea of having a spiral oil groove cut in the bronze bush, it seems totally logical to do so! Once I have obtained a replacement drain casting I can put it back together again!
Best wishes to all,
Mike.

[Simon]

Mike,
I think that new oil drain castings are available from Sports & Vintage.

[Ken Martin]

Pity I was too late to stop the skimming Mike. I just hope that Minor Man Paul Rogers - an upcoming scrut - for the VSCC is not reading this otherwise he will be out with his tape measure! The head skimming will not go down well in VSCC Light Car circles if you intend to compete. My car has 1934 hydraulic brakes and so I normally just do tours with the Light cars.
Regarding the cam I use - it is a 12/12 as they are the only ones available. I did reprofile my original camshaft making all the cams like the exhaust profile. I did it with stellite and a profiled grinding wheel with the cam mounted on the =saddle of a lathe. This was in the days when you had to mend things! This inadvertently improved the perfomance and when I fitted the 12/12 camshaft I didn't notice much difference much to my disappointment at the time in 1978.
ASre we sure that the M Types had a higher compression ratio - I thought not.

[halbe]

If one would want a higher compression ratio to get some more performance wouldn't a set of high comp. pistons be a good idea?
isn't it true that modern fuels need a higher ratio

Regards,
Halbe

[Ian Grace]

Here's the good word from Blower for the M.

"The standard depth of the cylinder head is 3.5", giving an individual capacity of 43.5 c.c. This is equivalent to a compression ratio of 5.5 to 1 (although 5.4 to 1 is qouted in the table on page 467). If 3/32" is removed from the gasket face of the cylinder head, the individual capacity will become 36.9 c.c. and the compression ratio will be raised to 6.2 to 1. The standard copper asbestos head gasket should be retained."

The M was quoted as delivering 20 bhp, which was increases to 27 bhp post chassis 2M/2024. I assume that the comp ratio was increased to 5.5 to 1 at this chassis number, which is when the 12/12 cam was introduced.

Are high comp. pistons available anywhere? I think I looked for the McEvoy, but didn't find any. Hornet pistons perhaps? Can't remember.

It's just my personal opinion, but increasing power a little bit, for me, is a case where safety trumps total originality if you plan to drive the thing - similar arguments can be made for the brakes, but here's where my thinking brakes down - because I personally prefer to retain the original pulley gear over Bowdens or hydraulics!

However, the day I see a LCES scroot measuring Minor cylinder heads with a steel rule will be the day I resign from the Section! (I remeber proudly turning up with my fabric saloon for my first ever LC event - at Roger Colling's place. Roger was the 'scroot'. I found him in the summer house. With a fatherly smile he boosted my ego with, "You have a very nice car." And he signed my chit. He'd never actually SEEN the car! )

[halbe]

S&V have four different types available ranging from 57 mm to 60.5 mm
I have to ad that the higher ones are Cosworth and 130 pounds each ............................................
Skimming the head is a lot cheaper but only takes about 2.2 mm off. so it is possible to obtain a higher comp. ratio all thought at a price
I suppose you'd also want a new crank and rods to cope with the increased pressure on the components.

Halbe

[mike houston]

I did look at a set of (6) Hornet pistons last week, and they were flat topped and presumably offered no advantage. I also looked at some alloy Hornet rods, but it all got too esoteric and complicated for me! I think I'll stick with what I now have. I'll next check the bottom end out, and if it looks OK leave well alone. I've got enough on my plate with finishing the body!
Regards to all,
Mike.

[DF9053]

I am not sure where you are all going with the high compression pistons - the pistons in and M type and a Minor come up to the top face of the block - if they come over this you have to be very careful that the piston and top ring do not catch on the head gasket.

On Mini's and the like this is done by having a raised D section in the top of the piston, that is away from the outer edge thus avoiding this problem. I don't believe that you can get pistions like this for Minors. The only options have flat tops.

The Woseley and Morris 10/6 Specials had a dome top to the pistion but the gudeon pin to top height was different and if fitted to a Minor con rod will not come up to the top of the bore - this will lower the compression ratio. The gudeon pin is also a different size so the rods have to be bored out to take the pin. Rings are also difficult to get for these pistons.

I thought the different sizes quoted by sports and vintage were bore sizes, M type 57mm P type 60mm.

Also general advice is never to use alloy con rods - they broke when new and will have age hardened even further by now - I have a set and spoketo a number of well respected people about using them - the answer was always don't do it!

I would stick with the standard pistion/rod set up and if you want to raise the compression ratio skim the head.

Cheers
Jeremy

[Toby]

I thought 10/6 pistons were the same as minors? or is it just the sv they fit? or neither?
Puzzled of Lymington

[DF9053]

Toby the 10/6 Specials had a higher compression ratio bought about by a dome on the top of the piston. However for both the 10/6 and the 10/6 special the pin to deck height is different to a Minor so the piston will not come up flush with the top of the block.

My Minor (DF) has these domed pistions and when the engine was rebuilt they had to be retained as the gudeon pin was larger and the rods had already been metaled without the engine place realising. We then had trouble getting rings but did find a plus 50 set in the end.

All good fun!

Cheers
Jeremy

[Toby]

well, thats a myth busted! saved me a few quid if i had ever come accross a set of 10/6 pistons!!!

[Ian Grace]

I fitted the longer rocker shaft rods on the Bed-Pan with the associated bronze rear carrier as I have seen the back end of the shaft break - this happened to Robin Harcourt-Smith last year on his CMS.

The evidence! Photo taken by Ken Martin on the 2007 Light Car Summer Rally. The weak point is obvious - the hole for the securing screw.