24 replies to this topic

[Welshminiman]

Evening Chaps, 

 

I'm currently in possession of a Pre A+ block which I picked up from fleabay some years ago. When I bought it, I discovered the block had been bored out to +30, which if my frazzled brain can calculate, is 1310/1311cc?? And the block had also been skimmed. 

 

What I'm looking for is a fast road sort of application, but being a pre A+, I would like to know what sort of limitations there is for this type of block?

 

I would like to achieve around 80-90 bhp (more would be nicer if possible), which has plenty of good low down grunt for quick acceleration. 

 

I'm also in possession of a 12G940 cylinder head, which will require modification (Leaded head at present) but I'm not sure whether it would be better modding this one, or exchange it for a ported & polished unleaded unit. Not interested in the 1.5 rollers, what would the 1.2 rockers be like (more out of curiosity) in this sort of application?

 

Please throw your comments at me, I'm not totally fixed on spec at the moment (other than the ultimate goal), so options/ideas would be greatly appreciated, and any info on the pre A+ block capability with this sort of spec would be even more greatly appreciated.

[Earwax]

Hi welshminiman

Lots of pre A+ blocks getting around in specs similar to your thoughts.The internals and the compatibility with new is where careful thought is required or newer parts ordered. eg slot drive on cam, oil pump, lots of thoughts on conrod suitability

 

Firstly , at rebore, you could choose to resleeve  or go 1330 or 1360 if bores didn't clean up .  at 1360 get machinist to offset.  the block skimming probably needs thought though, - as CR could be higher than ideal unless you use 10-11cc piston dishes. ( i know this because i just had one done and didn't have a lot of piston deck clearance. the head chamber size will also play a part, with the 21.?cc standard 12g940 chamber a possible issue ( i needed 23.7cc)-which was achievable with some good modding)

 

The cam, gearing and FD will have big parts to play with low down grunt, drivability etc.. On my recent build, i went Clubman close ratio in box, quaiffe ATB diff, cam similar to 276 and FD a lowly 3.4 ( this is only a weekend warrior, no long miles on freeways etc, no free lunch here - if you want nicer to ears on fwy then give a little low down grunt - however this thing will be near its cam band at all times)

 

Having just gone through this exercise, if you were talking flywheel horses/bananas etc, then yes it can be achieved with a good rebuild that is not far stretched or radical at all - however you may need to be prepared to lump up some cash to get a good bottom end, some flow in the head and a CR box

 

As stated many times previously, - this needs careful planning, measuring and consideration - and ultimately the choice of sticking with what is already there or starting the upgrade bandwagon is yours, but make these decisions collectively. to match components and work together with the build . ( For example if you go 276 cam - 1.2 rockers will be acceptable but 1.3 would possibly better matched to achieving your objectives

[Cooperman]

If it is at +0.030" that is 1301 cc, so a re-bore to +0.040" would give 1310 cc or +0.060" gives 1330 cc.

90 bhp is easy and can be reliable, although the more power you take from an engine the sooner it will be worn. This is mainly because more power = more revs and more revs = higher bore & bearing wear.

If this is a road car, don't be fixated by outright power as useable torque is much more important.

A 266 cam with a gas-flowed head, a new distributor with a different advance curve, a comp. ratio of around 10.3:1 with 21253 pistons, better inlet & exhaust system and an HIF44 carb can give up to 90 bhp at around 5700 rpm with excellent torque lower down.

Remember, you will never make a 55-year old design into a 'fast' road car, but it just won't be quite so slow in modern traffic.

[62S]

Provided it is a 12G 1279 block there is no inherent weakness.

What you do need to check is how much has been skimmed off the top. If it was just a light skim to clean it up that is fine but if it has been decked down to the height of a 970/1071 Cooper S block then you could be looking at a lot more expense. Guess who has been caught out by that before?!

[Welshminiman]

Where will I find the engine block markings? I've taken the pistons out of the block at the moment, so will have to put one back in to see how much clearance there is between the top of the piston and the block top.

[62S]

As you look at the back of the block the casting number is on the right hand side an inch or so above the flange.

If you have the pistons and they have numbers on the top then it is unlikely the block has been skimmed much.

[Carlos W]

Where will I find the engine block markings? I've taken the pistons out of the block at the moment, so will have to put one back in to see how much clearance there is between the top of the piston and the block top.

Obviously the piston will have to be on the con rod, and also on the crank and everything tightened up to be able to measure accurately.

Are they flat top or dished pistons?

[Welshminiman]

Dished pistons, I have them with me in work today so I can clean them up in our parts washer. Will try and find my piston ring compressor tonight once home, refit the pistons and check what sort of gap I got.

[Welshminiman]

Pistons are +0.030" and are stamped 21251 L12.

[Carlos W]

Have a read of this

 

http://www.theminifo...172270-pistons/

[Welshminiman]

Ok, now this has confused me, if the lettering (or numbering in this case) after the 21251 is the bore capacity, what is the L12 after it for? I have the +0.030" stamped above it (12 o clock position as you look down from above), and the 21251 L12 at the bottom (6 o clock)

[Welshminiman]

Will get a picture of one this evening, their currently drying alongside aircraft components at the moment!

[gazza82]

What bearing shells do you guys recommend? Welshminiman and I are building the same engine pre A+ ... mine at 1330cc with 12G940 head, although I think I will go with Mega pistons ... and my engine is inline not transverse (Midget/A35 conversion).

 

There are so many different makes around ... ACL, Vandevell/Mayle, etc ... I want ones to last ...

 

Any recommendations?

[albo]

hi,, if your pistons are 21251`s the reason your block has been decked is to raise the compression,,

as the 21251 is a low compression piston, you may find if you fit 21253 pistons they will be above your bores no matter what rebore size you chose,either stick with 21251`s or find a vergin block, ae 21250/ 21251 /21253 are verry similiar just different in pin height

good luck

[Welshminiman]

I don't think the block has been decked, I think its been skimmed to remove imperfections, as I can still see the tails in the block from the original ID plate.

 

This picture was taken sometime last year, before I started stripping it out.

 

 

This is what I'm confused about, what is this L12?? because the +.030" is at the top.