Blocks with casting hole
Turbo Mini Forums

I have two of the earlier 1275 blocks with the hole in the casting above the centre main bearing (casting number 12G1279) but one (possibly both) is on standard bore size, so plenty of rebore potential.
I have only one spare Aplus block (DAM4472), already on +030 and needs another rebore and it isn't even the one with the non-grooved mains.

Vizard says avoid the ones with the hole, but a search on this forum tells me:
(a) it may not be such of an issue on a low revving turbo engine providing the area is properly ground smooth,
(b) those blocks might have some "value" for historic racing or the such like.

So, has anyone actually used one for a turbo application (and did it crack) and what is this "value" for historic racing, ie, what does it mean ???

I need to decide which one to use so I can get it down the machine shop and know which size pistons to order.

Rod.

Schrödinger's cat - so which one am I ???

"Turbo's make torque, and torque makes fun"

"did you know you can toast potato waffles?"

Schrödinger's cat - so which one am I ???

You'll need to modify the main caps to swap bearing type. However, think of this.

1. Many of the Miniracers use the "old" type of bearing because they lubricate better. Plain bottom shell and high revs will cause big end bearing oil starvation if the main isn't X-drilled.

2. Other engines. How many have you seen with plain bottom shells?

This adds up in my opinion to that the "old" bearings aren't that bad at all.

When it comes to blocks, use what is suitable. Don't worry about the hole. I've seen plenty of holed race-engines, and got one myself.

The old A blocks are valueble in Historics becasue they are getting scarce. A+ blocks aren't allowed. (yet)

Just carefully file a new slot to accept the non groove lower bearing. The difference is in the cap and not the block.

The hole must make the block weaker but I suspect it will be good enough for anything other than a balls out racer.

The other advantage is that there are two bosses on the back of the block which make fitting a full flow filter a neat and simple operation.

Ifyou are concerned about the hole in the casting just give it a polish.

Regards
Dave

Edited by danboy on 17th Dec, 2007.

Thanks for your thoughts... I should have realised it's only the bearing caps that need modifying, not the block, as it's only the bottom halves that are ungrooved. !!!

I've already read the threads on cross drilling the crank when using the "plain" bottom halves, not quite sure I understand all those posts... but will think some more...

The casting hole is my main concern so I'll see if there are any more posts on this subject and, otherwise, try to "sell" the blocks with the holes on an exchange for an Aplus without, so all you "historic" racers, watch out !!!!

Rod.

Schrödinger's cat - so which one am I ???