DOHC conversion

Post by **youngun** » Sat May 16, 2009 4:48 pm

This is going to be a little sideline project alongside the main rebuild of the car.
But the plan is to do a BMW K series cylinder head conversion onto an A series. It will be the 8v head to start with as the 16v's have a hell of a premium on them. The plan is to get hold of a bog standard A series and then rebuild it, then plonk the BMW head on with a full brace of Bike carbs (to hell with fuel injection).
The K series head is designed for a 67mm Bore, which A series falls into that catergory?

anyone who knows about these conversions or has done one please share your experiences!

YG

Post by **bmcecosse** » Sat May 16, 2009 7:58 pm

You are looking at a 1275 engine - 70.61 bore. A 998/1098 is 64.59 bore - may be possible if you overbore +60 = 66.12. There is a LOT of work in doing these OHC conversions - not least getting the bottom half of the engine to stay in one piece with the extra power.

Post by **Roni** » Sun May 17, 2009 12:43 am

There is a lot of info here - http://www.ausmini.com , just do a search.
http://www.ausmini.com/forums/viewtopic.php?t=29923
Even a kit being made up for them. If nothing else, it is interesting reading.

Post by **bmcecosse** » Sun May 17, 2009 10:00 am

Indeed a very interesting read. So - for 'small bore' use - that 60 thou overbore will need to be 'offset' to match up with the head. Looks like 1275 is the better bet.

Post by **twincamman** » Sun May 17, 2009 1:05 pm

There's a feature on the Dep-o site
www.dep-o.co.uk

It's an on-line mag dedicated to modified classics, there's an interesting Minor pick-up on there as well.

Post by **youngun** » Sun May 17, 2009 5:19 pm

Got a guide on the way. Now I Have to source a 1275 or a 1098 and then a BMW K series head!

Post by **bmcecosse** » Sun May 17, 2009 9:18 pm

And all the other stuff - which they point out generally costs much more than the head!

Post by **youngun** » Mon May 18, 2009 7:32 pm

Im not going fuel injection. Not to my liking at all!

I have a good friend dealing in bike breaking and bike parts

so it shouldnt cost me much more than a pint and a tenner!

Watch this space.

YG

Post by **robertkemp** » Mon May 18, 2009 9:52 pm

specialist-components the company that does the kits are right on my doorstep fancy that. i'd like to see your progress with this build seem interesting,gonna be loud though

Post by **bmcecosse** » Mon May 18, 2009 10:17 pm

Especially the 'bang' as the crank lets go!

Post by **youngun** » Tue May 19, 2009 3:26 pm

Off to pick up an Ital Lump next week.....

Post by **superchargedfool** » Tue May 19, 2009 4:09 pm

Especially the 'bang' as the crank lets go!

why are so many people so hard on the a series when modded.

Mine is making well over 100bhp on a standard bottom end and is as happy as it could be with it.

Will soon have more like 140bhp on a sorted bottom end and I don't expect any issues.

Post by **bmcecosse** » Tue May 19, 2009 7:07 pm

Well - this DOHC is reckoned to give 150 - which is not going to do the standard crank any favours! In Minis - a tuftrided crank (with leaded bronze bearings) is used for anything over ~ 90 bhp. And the centre main needs to be at least strapped - if not replaced with a steel cap (with associated line boring). Lightened flywheel also helps crank life - crank damper essential - and full balancing of the rotating assembly - and the reciprocating parts will help too!

Post by **youngun** » Tue May 19, 2009 11:02 pm

150hp!!!!!! what have you been reading bmc?

The 8v head is rekkoned to give about 110bhp max on a 1275, and thats with the fuel injection system. Im aiming for 100bhp, with a view to going more mental when money permits.

YG

Post by **bmcecosse** » Tue May 19, 2009 11:53 pm

If you only want 100 bhp - that's easily done on a 1275 without all the fuss (and expense) of a BMW head! It's when you go beyond 100 that the serious expense cuts in.

Post by **youngun** » Fri May 22, 2009 4:59 pm

Project now on hold as the head gasket has gone on my Peugeot 306

Post by **RobThomas** » Fri May 22, 2009 5:51 pm

Midget 1967 thin-flanged blocks came as standard with EN40B Nitrided crank and Cooper S rods. Pretty unbreakable but rarer than hens teeth. (I've only got 2!!

)
I'd guess that you'd then need to get an ARP bolt set and centre strap to hold the crank in place for fear of the engine letting go and wrecking the whole assembly of expensive parts. Starts to look seriously expensive to make a good-'un.
As mentioned above, must be cheaper to get an iron headed A-series to make good power. I have some new alloy heads for A-series, too, but they cost a fortune!<br>

<br>

Post by **RobThomas** » Fri May 22, 2009 5:54 pm

These were designed for supercharged engines so it might be almost as expensive to make a Shorrocks-blown alloy headed A as to make a BMW headed one.

Bloody good fun for as long as it lasted, though!

<br>

Post by **Matt** » Fri May 22, 2009 9:14 pm

Rob

I have a '67 1275 sprite, is there an easy way without stripping the engine to tell if its one of the ones with the EN40 crank? Or even what engine number?

Post by **bmcecosse** » Sat May 23, 2009 12:21 am

Are you SURE the cranks are EN40B ?? If so - it will say so on the crank. But my understanding is only S engines had EN40B crank. The rods are NOT Cooper S rods - they look like them - but are inferior steel quality - but still far better than standard Minor rods of course! S rods are AEG 177. Spridget rods are AEG 625.