MG Metro cam and 12G295 head related query

[IslipMinor]

Now added to my favourites bar

As an alternative to adding a website to the 'Favorites' bar, it can be 'printed to pdf' using some free software called 'PDF Creator'. It is installed as 'Printer' and any website that you want to keep and not find that it has moved, or been taken down a some point in the future, is preserved as 'pdf' file on your PC in a folder of your choice.

When you are on the website that you want, go to 'Print' select 'PDF Creator' and follow the instructions. Obviously any links or other functionality on the original website are lost, but for links such as the 'Minifinity' one, it works very well indeed. Sometimes the page layout is not so clever, and also there are times when you will need to change the page orientation to 'Landscape' on the PDF Creator 'Printer' BEFORE you select 'Print'. After a bit of trial and error, it is very good.

This is the link to PDF Creator:

http://www.pdfforge.org/pdfcreator

This site is good, but often the 'Download' button on sites is for all sorts of things, apart from what you actually want, and can download default web browsers such as 'Bing'. Don't just accept the defaults, check very carefully what you are saying 'Yes' to please!

[panky]

I hope I'll be forgiven for a little hi-jack but I'd like some advice on the cam fitted to my 1275 Mini. It was bought off eBay a few years ago as a Piper 286 ( I can only find reference to a Kent 286) I've checked the identification marks against AC Dodds list and it would appear to have originally been from a 998 A+ engine before it was re-profiled. The car goes extremely well with the cam and stage three head, I have fitted vernier timing gear and 'dialed' the cam in to the 286 setting but would like to make sure I've set it to the right cam - ie is this a 286 profile or something completely different
This is the stamping on the end of the shaft, over-stamping doesn't make it easy to identify.[frame][/frame]

[philthehill]

Looking behind the over-stamp numbers the original stamping indicates that it was (and may still be) a Piper HR270 camshaft.

Mixing up the numbers somewhat the numbers could have been miss stamped and should read Piper HR285/2 camshaft.

[panky]

Thanks Phil. Just looking back at the build thread I posted on Commervanfan a few years ago and it is indeed a Piper 285, my memory failed me again So quite pleased with that. An extra 14 bhp, and according to the Piper site it's the 'Ultimate Road' cam with a very wide power band That, coupled with the stg 3 head, makes it a pretty quick motor - as I found out
I will double check the valve timing though while the engine is on the bench.

[814XUW]

Thanks all for your input. It has been noted. My next move will be to pull the cam out (while fitting the 295 head) and double check it is an MG Metro cam. If it is I will dial it in from there, and let you know how it goes.

[panky]

Thanks for starting this thread I learned a lot and it's given me peace of mind too

[philthehill]

Panky quote above:-

"my memory failed me again So quite pleased with that" !!!!!!!!!!!

I hope not

[panky]

Forgotten already

[BrianHawley]

Is this a stock 12G295?

If I recall rightly, they are fairly high volume. Have you checked your compression? We used to skim them quite a bit for the non-1275 mini engines. Or fit a blower

If you do need to skim, it was possible to break into an oil way on about one in four of them. But it's fixable by welding and reskimming.

[philthehill]

For information:-

The 12G295 head has a combustion chamber of 28.3cc whilst the 948cc Minor has a combustion chamber of 24.5cc. The 1098cc Minor fitted with the 12G202 head has a combustion chamber of 26.1cc.

It is usual to skim the 12G295 head by 0.060" when fitting to a 948cc or 1098cc Minor engine with standard pistons.

To determine if the head horizontal oil way is in danger of being exposed when skimmed - measure the depth of the oil way down through the head (hole is in No: 1 rocker pillar seat) - the nominal thickness of a standard 'A' Series head is 2.75". So subtract the depth of the oil way from 2.75" and that will give the thickness of the metal between the bottom of the oil way and the face of the head. There must be at least 0.060" of metal left between the oil way and the head face after the head is skimmed.
As Brian says above it is possible to repair but better not to go there if possible in the first place.

[BrianHawley]

For information:-

The 12G295 head has a combustion chamber of 28.3cc whilst the 948cc Minor has a combustion chamber of 24.5cc. The 1098cc Minor fitted with the 12G202 head has a combustion chamber of 26.1cc.

It is usual to skim the 12G295 head by 0.060" when fitting to a 948cc or 1098cc Minor engine with standard pistons.

To determine if the head horizontal oil way is in danger of being exposed when skimmed - measure the depth of the oil way down through the head (hole is in No: 1 rocker pillar seat) - the nominal thickness of a standard 'A' Series head is 2.75". So subtract the depth of the oil way from 2.75" and that will give the thickness of the metal between the bottom of the oil way and the face of the head. There must be at least 0.060" of metal left between the oil way and the head face after the head is skimmed.
As Brian says above it is possible to repair but better not to go there if possible in the first place.

Thanks Phil. It's all coming back to me. Been a decade or three since I skimmed a 12G295.

[panky]

Armed with the AC Dodd information I dug out the cam that was originally fitted to my Mini and surprise oh lovely surprise it's MG Metro, I know where that will be going

[814XUW]

Well, it's back to me, and back in one piece.
Measured depth with my micrometer, measures 2.604", I think all standard heads are 2.75"(?). Which presumably means this one has been skimmed by around 15 thou in the past.
Is it worth, according to the advice here, fitting flat top pistoms? Trying to avoid messing the head up for someone who may need it sometime down the line from me (if nothing else).
Am I right in thinking that 998 Mini pistons (early type with circlip) are the same as Minor 1098 ones? If so I may look to fit these - http://minispares.com/product/classic/ADU3490-20.aspx (just need to work out if they come with rings or not - in the pic they do but not in the listing!). Vizard quotes the pistons as having a 10cc dish (from what I remember reading earlier today) which gives compression of 8.3-1 (again from memory), by fitting flat top pistons presumably I'm restoring this compression ratio (more or less)? By fitting these pistons, does anyone know how it would behave if I ever had to revert back to a standard 202 1098 head (if need be)? I've done a few builds but they have been very much off the page builds and I've never dabbled with adapting the CR. So TIA again!
PS - Vizard quotes the MG Metro cam as being timed at 110°, he also states that you should aim for 1° advanced to compensate for timing chain wear but I suspect as close to 110 will do for a road engine. He also specifies 15 thou for the valve gaps in place of the conventional 12, which I didn't know!

[philthehill]

The pistons in both the 1098cc and 998cc engine have fully floating gudgen pins secured with circlips with bore diameters of:-
998cc bore is 2.543"
1098cc bore is 2.543"

The stroke of the 998cc is 3.00

The stroke of the 998cc is 3.296"

The height of a standard flat topped 998cc piston above the gudgen pin is 25.7mm.

The height of the piston above the gudgen pin is the measurement you need when comparing 998cc pistons and 1098cc pistons.

The engine will be perfectly alright if you have need to revert to a 202 1098cc head.

As mentioned above - If you want max performance be aware that the cam timing details are only base info and only on a rolling road or comprehensive road testing will you be able to determine if the cam timing (and everything else) is right.

Even the standard 'A' Series works better with 0.015" valve gaps but can be a bit noisy.

[814XUW]

So from that info I just need to ask Minispares what the height is from the gudgeon pin on their pistons?
Alternatively, where else can you get flat top pistons for a 1098 off the shelf?
Thanks for your help Phil, we'll get there!

[philthehill]

Try

http://www.petermayengineering.co.uk/index.htm


htm//www.petermayengineering.co.uk/catalogue7.htm#catalogue7

[814XUW]

Hi all, able to update now!
Fitted the 295 head, was very impressed with performance. Unfortunately, I didn't have it skimmed as it looked ok on the steel rule, coincidentally my engine man agreed, and it blew into the water jacket, so needs skimming again. I have since spotted some very minor pitting to the surface, pays dividends to have them skimmed as a matter of course I would say now. I may as well get it skimmed to correct the compression ratio now! Old head refitted and, having been to France and back since in it, I can deduce it was that head.
Also, cam was 4 degrees out so fitted an offset key, hard to tell if it's made a real difference but at least I know it's right.
Thanks for the input.