1275 Block options

Post by **minor_hickup** » Sun Dec 21, 2008 5:48 pm

Ok, I've been gathering bits to build up an engine for my current project and I'd like to start putting it together while its still too cold to start prepping the bodywork.

I'm trying to decide which 1275 block to start with, I can get hold of a midget engine no problem, there's a marina engine been offered to me and I'm sure I could always look for an Ital block. However with my research I've got confused. I know the midget engines, especially the earlier ones have cranks made of stronger steel and have lighter stronger rods with a smaller big end bearing size and the later A and A+ blocks have cranks and rods made of heavier but lesser grade steel with larger bearings. However the A+ block is stronger and ribbed.

Personally i would have thought the midget engine would be the best place to start for a performance build, I'm aiming for 100bhp (although staying realistic about what it will actually achieve). However I thought I'd ask here as I'm sure there are a lot of people who have done this before. Also I wanted to know if the midget crank can be used in the Ital block to get the best of both worlds.

Finally (last question I promise), there is a lot of talk in Vizard's book about crank hardening (nitrided and tutrified). i know there are some rare factory hardened cranks but is it still possible to get this done to a standard crank?

Post by **bmcecosse** » Sun Dec 21, 2008 7:06 pm

I'm currently building a Midget block - with a Marina crank in it! The Midget conrods are expensive - if you don't have any - and frankly the standard Marina crank and rods are just fine. Midget crank will be v expensive too - if you don't have one. Yes you can have a Marina crank Tuftrided - no real point unless you are going super or turbo charged. Again - it's not cheap - and the crank needs grinding again afterwards. Duplex timing gear is best. Big valve head with the full Vizard treatment - 544 camshaft and single 1 3/4" HIF carb on ally manifold with best LCB and exhaust you can afford should give you ~ 100 bhjp without going for stupid high revs.

Post by **minor_hickup** » Sun Dec 21, 2008 7:20 pm

Well I already have a very worked over big valve (37 and 29mm IIRC) 12g940. i was going to use this with a Piper 286 cam which is like a 544 I believe. I can get hold of NOS HS6 carbs so I was going to port and match a manifold to the head and then give the carb the vizard treatment on the throttle spindle.

However if the Ital ribbed block is stronger would it take to boring better? I was going to bore out +60thou to give 1340cc. As for midget rods and crank, I was considering buying two 1275s, making one good engine and putting together a second one (midget block and ital internals) if this is possible and punting it on to make some cash back.

Post by **bmcecosse** » Sun Dec 21, 2008 7:27 pm

Sounds good - you can bore either block (but check to see if fitted with liners) - but really not worth it unless it NEEDS boring anyway. The difference in power from 1275 to 1340 is hardly noticeable - so if the block has good bores /pistons - just use them ! Yes - you can mix and match internals - just need to get flywheels to match the crank tails.

Post by **minor_hickup** » Sun Dec 21, 2008 7:37 pm

Well I can only get hold of blocks that are sold for 'reconditioning', i figured if I'm going to bore them I may as well bore them right out. I've asked for a maniflow large bore manifold for christmas!!:)

Post by **Matt** » Sun Dec 21, 2008 8:51 pm

MH

I have an A+ ital lump you (or anyone else) can have. Its currently +60 but the bores have gone oval, the crank is badly scored but may be recovered by - 40 grid (but I doubt it), 3 rods with low comp pistons which are useable - im keeping the scrap one, and the cam thats in it.

Engine dumped its oil when I was doing 85mph odd (tall diff and tyres)

No backplate/flywheel - they are already claimed, but would be ideal for you to compare the different parts. You would have to collect from Haywards Heath when im there

Post by **jonathon** » Sun Dec 21, 2008 9:00 pm

MH, were just building a 1360cc which will produce around 80-85bhp and similar figures for torque. It might be a poor man's 1380cc but you can save lots of money going this route and achieve almost the same power figures. Add a good head cam and carb and you are on your way to producing descent power

Post by **minor_hickup** » Sun Dec 21, 2008 9:33 pm

So how is the 1360cc capacity achieved? I take it that it does not require an offset bore?

Oh and Matt that may be useful for a reference, haywards heath isn't too far from me. I may try and find a decorative use for it afterwards!

Post by **jonathon** » Sun Dec 21, 2008 9:48 pm

Its a + 80 bore, which does not require off set boring yet retains plenty of wall between cylinders.

Post by **les** » Sun Dec 21, 2008 10:23 pm

yet retains plenty of wall between cylinders

You're the boss Jonathan, but is that right?

Post by **jonathon** » Sun Dec 21, 2008 10:27 pm

T'is true, I'll sort the data specs tomorrow and post then

Post by **bmcecosse** » Mon Dec 22, 2008 12:23 am

Hmm - i've seen a +60 bore and it leaves very little between bores!
For a road car - I say keep down to the minimum rebore you need to clean up the bores. More reliable engine - and really only giving away 2 or 3 bhp to a 'big-bore' engine. Been there/done that with Mini engines - the unreliabilty issues just don't justify the tiny bit of extra power. The large pistons also tend to cost a small fortune !

Post by **jonathon** » Mon Dec 22, 2008 10:45 am

The idea of the 1360cc is not to give all out power but more to offer much improved torque. Our engine will be mated to a 5 spd Ford box so torque ,not ultimate power is our priority.
I agree that minimum rebore is 'safe' but I'd like to see the evidence for 1360 or 1380's being 'unreliable'. My engine builder is very well versed in hot A series and has build many race units over the last 40 odd years. So I'm quite inclined to listen to his advice and experience in this matter.
The Pistons are about £190 retail and the full rebuild inc unleaded head and fully balanced bottom end is £950 plus VAT.

Post by **les** » Mon Dec 22, 2008 10:12 pm

The resultant thickness of the wall between the centre cylinders would be 2mm ?

Post by **minor_hickup** » Mon Dec 22, 2008 10:38 pm

Thanks Jonathon, I may stick with a +60thou bore so I know I always have the ability to bore again without offset bores, which may not be possible after a +60thou bore. Still I haven't started yet so may change my mind.

Post by **jonathon** » Mon Dec 22, 2008 11:03 pm

Sorry Les, missed the engine builder as we left pretty late tonight.
I'm collecting the motor tomorrow so should have the info for you in the evening.

Post by **jonathon** » Tue Dec 23, 2008 9:48 am

Les,
The measurements are 132 thou between number two and three cylinders and 155 between one and two and three and four.
As for reliability they have just refreshed a 1360cc mini motor that has covered 100,000 miles, I'd say that 1360's and 1380's are reliable if not tuned to the hilt, or constantly subjected to sustained high revs.

Post by **les** » Tue Dec 23, 2008 7:52 pm

Thanks for the update, I'm making 0.080 = 2mm, so your figures suggest 3.3 something mm! Rather safer than my estimate of 2mm!

Post by **bmcecosse** » Tue Dec 23, 2008 8:06 pm

Yes - but it's still ~ 1/8" - look at a 1/8" drill bit - it's not much! But by all means - go ahead - if you can justify that expense.

Post by **jonathon** » Tue Dec 23, 2008 10:40 pm

What do you mean by 'if you can justify that expense.' Its a cheap version of a 1380,offering good power with a std MG metro head and very useable torque. I do not see the build cost as expensive though. 'look at a 1/8" drill bit-it's not much!', no its not, but is clearly enough, so as not to produce reliability issues.
I had a look at another 1360 mini engine that they were building and the std gasket thickness between the cylinders is slightly less than the 1360 bore.
The 1360 is no less reliable as an offset 1380 and I have yet to hear of an unreliable one of those.