7 replies to this topic

[amsgw]

Hello :)

 

I bought a beautiful 1981 Mini City, professing to be a no-issues smooth runner, with nothing but a hard-can-it-be attitude and experience on a cantankerous 1983 Land rover Defender. I'm a relative noob when it comes to engine building, having only had the previous 'training' of 'how do I fix this now broken thing'.... turns out the broken thing was my big end bearings. 

 

A year and a lot of learning later, I'm now at the buying and rebuilding stage of this unplanned refurb and am looking for advice and tips on my current engine build plan. My local mini shop and this forum have gotten me so far, now for the final details :) the aim with this build is for a happily usable, often-as-she'll-let-me yet swift run around. I'm not after mega power, though after coming to the conclusion that I'm starting to get the bug, I've opted to err on the side of performance pieces where there was a nominal difference in part price, with the idea that I may well want to start upgrading her in the future. Why spend so much just to replace the same pieces later down the line. 

 

Specs as I have them now:

12G949B head. Has 16F2 on a screwed-on plate(?) on the head, but can't find any info on this marking.

1275cc A+ engine. Machinist confirms she needs +20 thou bore

CAM6232 crank. 3rd journal was heavily worn (all 4 big end bearings were spun but this one was destroyed and splintered) so all big ends are being ground +30 thou, plus mains +20 thou

Cam has been identified as the OE 1275 A+ sprite/injection 50hp cam. It shows small wear on lobe 8 but machinist believes this to be fine for the application. Has been micropolished

Hif44 carb with cone filter

Old LCB standard exhaust was cracked at the point where the branches join, rather unsightly rust throughout too

Dizzy as yet unidentified, but given the state of the leads, rotor arm, coil and dizzy cap on disassembly I'm working on the idea that the dizzy is past her use by date

 

Also running a standard rod change gearbox, standard diff. Looked into X pin - think this may be overkill for the application but would consider it later down the line. On tear down, both box and diff seem in good condition. 

 

What I'm now looking to rebuild to:

1293cc block with 10:1 compression ratio

Minispares evolution pistons

No change to crank or cam, just the grind /polish and fresh bearings to size

Keep the hif44, tear down and rebuild with a repair kit just to begin from a good base (on confirming the big end failure diagnosis, my local mini specialists got her running well as part of the issue was a broken carb spring making it impossible to tune the carb, making for funky running. They were happy with the carb at that stage but it's since been taken out during engine removal)

Maniflow Cooper freeflow exhaust system, single silencer with centre exit for a nice sound, good economy and no wasted power

Dizzy - C-27H7701 on mini spares

Also replacing of course the oil and water pumps, timing chain (sticking with single chain), clutch and coil as a minimum.

 

Already replaced in the effort to narrow down the problems at the beginning (to name a few) were the HT leads, rotor arm and dizzy cap. Old radiator swapped for a twin core. Head was cleaned up, skimmed 20 thou, with valve seats recut, guides checked and new valve stem oil seals put in (will replace now the head has been off again).

Once she's all back together I'd like to get her on a rolling road (handily we have a mini-specialist tuning shop with a rolling road within 30 mins from me) and get her tuned nicely to release the true power/performance from this set up. 

 

My concerns/ areas for advice:

Machinist hasn't seen the conrods but having seen the crank, he thinks I need a new conrod #3. Do I need to/should I replace all 4 at once - I don't have funds to replace for new or forged, it will have to be a clean up and hone job on second hand ones.

Is a 10:1 CR correct for this application/set up?

How well recommended does the X pin diff really come?

ARP head and conrod bolts - are standard just as good for a road application? This is something I would change if looking to do a performance upgrade but does road require it really?

I was debating a stage one kit but I'm basically there with the work already done, though should I be looking at upgrading my carb needle when I rebuild it?

I'm currently getting a 23.6cc reading for head chamber capacity. To my research this is larger than original - could it have had work done already?

Should I be replacing the valve springs whilst I'm in there? 

Is there anything else I should consider upgrading / doing some work to whilst I'm here?

 

Sorry for the long read - hopefully it will turn some gears in the heads of the great engine builders on here who can tell me if and where I'm going wrong before I steam ahead!

[KTS]

personally, i would replace the camshaft with something a bit more capable; something like the minispares evolution001 camshaft would be one option

[alex-95]

10:1 Compression would work but a bit lower would be better. 9.75:1 is recommended.

Take out all the core plugs and Oil gallery plugs before taking the block for machining and make sure all the oil ways, bores etc are cleaned out (usually takes multiple attempts to get them properly clean).

I'd change the Camshaft if you want a bit more power.

X pin diff's are very good, but if you're not aiming for loads of power then a rebuilt standard diff should be fine.  Adding a central oil pick-up is recommended. You may find that the centre main bearing on the gearbox needs replacing.

The problem with the current new standard studs is that they are prone to snapping when torquing them down, The original ones are worth keeping if they're in good condition.

I'd recommend getting an AC Dodd 0 tolerance Oil pump from Thomas classic and modern.

Pointless getting a stage one kit as you basically have everything from it already, It's worth buying a decent branded Filter if you've not got one already, The cheaper cone filters aren't that good.

 

The Needle doesn't really matter, If you take it to a tuner then they should know how to polish the needle to suit the engine build. Use a BEJ for the initial start up as this is a lean needle and then BDL for the running in driving as this is also a lean needle so won't wash the bores out. Have a read of this for running a new built engine https://www.calverst...in-new-engines/

 

It's definitely worth rebuilding the carb with the full rebuild kit and get one with a smooth throttle disc http://www.minispare...67.aspx|Back to

To get the most out the engine it'd be worth getting the distributor re-curved (AC Dodd can do this) 

[amsgw]

Brilliant thank you! How would you recommend cleaning the oil ways etc. I’ve found them difficult to access and didn’t know how rough to be with them eg stiff wire brush or not. I’ve read so much about compression ratios but I don’t feel confident… what is the benefit of a 9.75:1 vs 10:1 in this application? For context before I tore her down she was always running on high octane fuel and I’d continue this.

Really interesting reading thank you!

[Cooperman]

The above advice from Alex is excellent.

The Evo001 cam would suit you perfectly for a road engine. A 10:1 CR is fine so long as you use E5 97 RON petrol and will give just that little bit more.

Remove the oil gallery plugs and wash out the galleries with a good engine cleaner and finish with a small piece of clean rag dirred in cleaner on the end of a long piece of wire - a straightened out wire coat hanger with a hook on the end works fine. Fit the new plugs with a bit of Loctite.

I always use a Metro-Turbo oil pump from Mini Spares, having had issues with the standard ones.

Of course, you can go as far as you wish with an engine build and keep spending money, but in the end so long as all the parts are in good order and you have new bearings, pistons, oil pump, water pump, timing chain, etc, you'll be fine assuming the crank journals are re-ground. Set the crank end float to between 0.002" and 0.004" if you can.

 

I hope this helps.

[cal844]

Distributors can be rebuilt and recurved to suit your new engine specifications.

AC Dodd is your man for this and also get a zero tolerance oil pump

[alex-95]

Brilliant thank you! How would you recommend cleaning the oil ways etc. I’ve found them difficult to access and didn’t know how rough to be with them eg stiff wire brush or not. I’ve read so much about compression ratios but I don’t feel confident… what is the benefit of a 9.75:1 vs 10:1 in this application? For context before I tore her down she was always running on high octane fuel and I’d continue this.

Really interesting reading thank you!

I used a long pipe brush when I clean mine and then clean lint free cloth and spray with brake cleaner or similar. 10:1 will be ok with the higher octane but the higher compression ratio isn't required for mild cams - have a look at this article https://www.calverst...considerations/

[amsgw]

Amazing insights thank you all :) so is the consensus to have the existing dizzy rebuilt and recurved by ACDodd, or would it be better to buy the new one to recurve? Could anyone explain that more for me, how recurving works and what it achieves?

Re the CR, if I’m understanding the article correctly Alex 95 surely I would be erring on the side of 10:1 with an expectation of reduced VE in reality? Or have I got that wrong?

Also does anyone have an opinion on which oil pump is best, 0 tolerance or metro turbo?