paul_mcq
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| posted on 16/1/05 at 07:06 PM |
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unleaded?
well lads just bought a mini gt there and looking to modify the head. need to no how to convert a head to unleaded fuel? is it something to do with
porting?plz get back to me
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craig1410
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| posted on 16/1/05 at 07:34 PM |
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Paul,
It's usually more to do with the valve seats. You will need to have hardened seats fitted if it doesn't have them already. It's also
worth getting them cut as three angle seats while you're at it as this will improve flow slightly and should give a better seal.
If it's a late head then it might already be unleaded compatible but don't be tempted to just "see what happens" because the
Mini will wreck its head if fed with unleaded fuel unless the hard seats have been fitted.
Hope this helps,
Craig.
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paul_mcq
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| posted on 16/1/05 at 07:36 PM |
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how late would be late. the car is a 1980 1275 gt. would that be late enough
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craig1410
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| posted on 16/1/05 at 07:47 PM |
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No, I was thinking more of the Cooper's of the 1990's.
I used to have a 1978 1275GT and it certainly didn't support unleaded fuel. However, it is possible that yours has been converted by a previous
owner. If I remember correctly I think there is an industry standard(ish) mark which machinists apply to castings when they fit hard seats. Maybe
someone else will be able to remember what it is?
The other option might be to pick up a more recent Cooper head from an engine from the mid 1990's. If all else fails, getting new valve seats
fitted isn't a big job and any decent engineering company should be able to help you out. Shouldn't cost that much either.
Cheers,
Craig.
[Edited on 16/1/2005 by craig1410]
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paul_mcq
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| posted on 16/1/05 at 09:49 PM |
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does any one no the process of changing the seats or has done it themselves? plz get back to me cheers
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Mark Allanson
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| posted on 16/1/05 at 10:14 PM |
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The older A series head does not have a seat insert, the seat is machined directly into the head. The machinist has to rebate an area of the valve
seat to accomodate the new seat insert which is pressed into position. It costs about £10 per valve (£80), but you have to supply a stripped down head
for them to modify.
I think it would be cheaper to get a 1992 on head from a scrappy, easy to check - the donor car will have a cat.
If you can keep you head, whilst all others around you are losing theirs, you are not fully aware of the situation
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Peteff
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| posted on 16/1/05 at 10:34 PM |
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I read somewhere, probably an old Miniworld magazine, that only the exhaust seats really need doing. You could use Millers lead additive and octane
booster instead. Don't butcher the head without looking into the reasoning first. It doesn't automatically make them flow better.
http://www.minisport.com/classic-mini-shop/products/hi-tech-engineering-performance-tuning/remanufactured-cylinder-heads/remanufactured-unleaded-cylin
der-heads/remanufactred-cylinder-head-for-1275cc-product.html
These do a remanufactured head and loads of parts, used them years ago for suspension parts though.
[Edited on 16/1/05 by Peteff]
yours, Pete
I went into the RSPCA office the other day. It was so small you could hardly swing a cat in there.
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wilkingj
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| posted on 16/1/05 at 10:44 PM |
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A mate of mine used is 4 pot Land Rover daily, and clocked up 40k miles before he had to change the exhaust valve seats.
I drove my Landy 4 pot petrol, for 4 years on unleaded, and its still going strong (sold it last year to fund the Viento).
I would run it until you needed to fix the head. Why pay for work now, that you needn't do say for a couple of years?
1. The point of a journey is not to arrive.
2. Never take life seriously. Nobody gets out alive anyway.
Best Regards
Geoff
http://www.v8viento.co.uk
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craig1410
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| posted on 16/1/05 at 10:55 PM |
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Guys,
From memory I think the A-Series running on unleaded has a history of burning out the seats sooner rather than later. Bear in mind this is an OHV
engine with adjustable tappets and unless you fancy adjusting the tappets every couple of months to compensate for valve seat recession then I'd
recommend that you do something proactive. I'd agree with Mark however and recommend you try to get a mid 1990's head complete rather than
mess around with rebuilding an old one. If you do then make sure the combustion chamber is the same size or compression ratio will be affected.
I'm not sure if later engines had the same sort of pistons as the older ones (eg. dished, flat top etc) so worth checking.
If you do decide to rebuild the head then I'd replace the valves with slightly larger ones. I think 1.4" was good for fast road IIRC. The
ones to go for a few years ago were "Rimflo" valves which had a slightly dished face which prevented flow reversal with hotter cams. Also,
change the valve guides at the same time (easy and cheap) as this will reduce oil consumption and is recommended any time you change valves.
It's all coming back to me......mispent youth and all that! I've still got my copy of the David Vizard A-Series Tuning Manual in the
attic!
Cheers,
Craig.
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