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MG Midget and Sprite General - how much to shave off cly head to raisethe CR 1 pt

As General rule

How many thousands of an inch shaved from the cly head...would result in 1 point of CR...ive heard its .013... But i cant verify that

Agian... This is not exact ...but a general rule, obviously the more that its shaved at its max the higher the compression ration

This is for an A-series 1275 with NO chamber modification

Thanks guys

Prop
Pro P

Go on then this should be good,

Why do you want to know that?
Robert (Bob) Midget Turbo

Im not saying...to depressing and angry at the same time


But i need to know to see what options i have left.

Any ideas as to the info i need

Thanks

Prop
Pro P

Maybe go back to a stock head?
Those seem to run pretty reliably and there are more than a few available.
Just a thought, don't shoot me.
Rick Bastedo

Am I right in guessing, the engine shop skimmed your head, and your really peed off they did it?


Lawrence Slater

Or has Prop discovered an aggregate 1/10" is missing and he is wondering what compression he has been trying to run?

What exactly do you mean by 'one point', is it 1.0 eg 9:1 up to 10:1, or is it 0.1 eg 9.5:1 up to 9.6:1?

Prop, again, a notebook and pen. Measure and record everything as you go - date it and note thoughts/advice relevant to data.

Roger T

Prop
If I remember correctly you cc'd your head before and it would be in the archives here I'm sure or you might have it down somewhere.
You've just had your valves reseated so they would be a tiddle lower in the head lowering the c/r a tiddle and I'm guessing you have had the head skimmed and that would restore the c/r
The ONLY way to know for sure is to cc it and compare against your previous spec- Really if is only a few though, forget about it and motor on--
Cheers Willy
William Revit

Oops sorry Roger I hadn't read through your post completly , I agree though, measure it and write it down
Cheers and Merry Christmas
Willy
William Revit

Thanks guys

I got it figured out...bottom line, im screwed

Yeah... The head got radically resurfaced....the head is now between 11 and 12


So i my new winter project is building a new cly head

A word to the wise....never piss off the guy cooking your hamburger or the guy machining your cly head...esp if the have a jesus christ of the drill press atitude




Im still so freaken ticked off and just seriously depressed and its now days later...so im not even talking about it.

Prop
Prop and the Blackhole Midget

Prop, if it was me I'd try to take a "what is past is past" attitude for my own sanity and move on.
Like I said before, you can get a 1275 head bone stock and have it freshened and get it on and get driving.
Wouldn't you like to just drive the car?
Just my 2 coins, do what you will.
Rick Bastedo

That's a real shame Prop. For them to quote 8 weeks for a one-day job and then go and do that!! Why were you getting it skimmed anyway? From the earlier thread photos I thought that the head surface was good. And wasn't this fully rebuilt and surfaced just a couple of hundred miles ago? Why would it need resurfacing anyway!

But Rick is right. Get a new head, quick freshen up and get it sorted. You can arrange for your Italian friends to visit the machine shop later!
Guy

No chance of going back? Not for work but for some compensation (I at least hope they did not charge you for screwing up)

No chance of grinding it a bit bigger?

Onno K

I take it they are paying for the new head Prop?
Lawrence Slater

The head they will be paying for should come off a horse.
Guy

Thanks rick... Thats the approach im trying for live and let live in the past...

im not paying for the work and we are still figuring out a remeady.. And the idiot got fired, Mainly a last straw on his part....it was only supposed to be skimmed .005 but, sh*t head needed to retailate.

So another head is the word of the day...im looking at the new head as an adventure to try some new ideas i wanted to try for modifying the head... I want the exact same head as the one i have know...but just some better ideas on how to make that happen...so i want to video the work for youtube...should be intresting

Well thats what im telling myself anyway...im just glad its winter...amd the roads will be bad in a 2-3 weeks ... So once the roads are good agian ill have this project in my rear view mirror...and im good to go...

The thing that just guts me... I had finally killed off the last of the grimlins... And that was all i did last year was de-bugging and killing off pop up grimlins...yeah 1/2 where my own making or mis-diagnoises...but gez... I was there... It was finally a worry free daily driver.

As we say... Welcome to spridget life.

Prop
Prop and the Blackhole Midget

LOL OI Guy :P No amount of horse transporter details will redeem yourself from that :)!!!!

Nice to see that some people were willing to hear poor Prop's terrible experience, and help, not dismiss it callously, and it's a good lesson for the rest of us - ONLY get your head done by someone who KNOWS what they are doing, and don't be fobbed off by "we're keeping an eye on them" - when quite obviously, they didn't.
rachmacb

Reference to the Godfather, Rach. Seems like Prop's engineers need to be sent a clear message. Lol !
Guy

LOL I saw the film, and wasn't impressed with that head either ;)!!!!!

They sure do - I personally heard once of someone who was going to throw a Diff through someone's window .... perhaps something like that might be more appropriate - and cheaper ........ although, there was a woman in Ok who stole some of her fellow competitors horses and cut one of them up ............ crazy unhinged people - fancy getting that overly competitive!!!!
rachmacb

I've got an old busted diff that can be used.
I just want postage ;P
Onno K

Prop - serious question - do you know the octane rating of the petrol available to you in your area? If you are able to access sufficiently good petrol (or use an octane booster) then a CR of 11:1 could be OK on a road car - 12:1 sounds a bit too much for road use though... I'm assuming you are running reasonable spec electronic ignition (points have a tendency to scatter too much with high CR)

My old 1293 road Midget was fine running at 11.5:1 CR with a 296SP cam, 97RON petrol and set at 26' total advance - no piston damage through pre-ignition in about 15000 miles of road (and light competition) work. Remember that the ignition curve set up is hyper important when the CR gets marginal...

You do need to measure your chamber and above ring cylinder capacity at TDC to do a proper static CR calculation - estimation and guesswork won't help you - you can get scientific burettes on ebay - Vizard goes into it in his book I recall...

Best wishes

James
James Bilsland

Would not try a 11-1 CR with an SW5-07.
Cam (overlap) makes a lot of difference in that department
Onno K

Thicker than standerd copper gaskets are available.
darnoc31

Could you get a standard gasket and make it extra thick with some aluminium tape either side ?

Sorry ;-).
Dean Smith ('73 RWA)

Hahaha.... Your sick dean

Im really resigned to just building a new head, even at 10.5 CR, im just not comfortable...as you say ignition becomes uber important, and with fuel being complete trash... I just dont want to risk it

Im guessing cometic must have taken early christmas there the only real viable option left... But i just dont feel good about that idea

So im really thinking another head is a better idea

Besides with winter almost here.. if i shovel 6 drive ways of snow, then ill have the cash to build another head.

Prop
Prop and the Blackhole Midget

Prop
10,5 is a very normal CR to run with an SW5
You surely should try that I think you will love the added grunt
Onno K

Prop


Remember all that measuring and stuff that went on before to get you a comp. ratio that you could run your crappy fuel on without having to run additives or have to run your timing right back.
If I remember correctly it was about 9.7 which let you run your timing up where it should be without the worry of detonation.
You can run higher compression and gain power but it all gats a bit borderline in the tuning dept. when you're up against the fuel we get now.
My suggestion is to keep the compression the same as you had before and save yourself a lot of heartache

How much did this guy take off your head ???? I've got a couple of mates I could send over and make him put it back on if you want---

Seasons Greetings all
Willy
William Revit

This thread was discussed between 17/12/2011 and 21/12/2011

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