701M Block Rebore Sizes

[AlfaLofa]

Information is available regarding re-boring of LB, LA and LAA blocks

- But what's the recommended max re-bore for a 701M block?

(I ask because I have a 701M block which is currently +30).

Also am I correct in thinking that a +40 re-bore equates to a cylinder bore of 83.50mm

[types26/36]

Your 701 block should be stamped on the front face (water pump end) with the LA/LB number but irrespective of that as I recall Lotus only supplied +15 thou oversize pistons so draw your own conclusions
Pistons are available in various sizes from the after market people but an ultrasonic check would probably be needed.
Yes a +40 thou bore would give you an 83.5mm bore.

[Craven]

Hi,
Ford original bore sizes were given in imperial units, inches. Hence standard Twin Cam bore is 3.250 inches. So + 20 = 3.270, + 40 3.290 and so on, conversion to metric size depends on what ever factor used. Remember there are machining tolerances that go along with any numbers you come up with.
For what it?s worth.
Ron.

[rgh0]

The block casting type ( eg 70m 711m 681f etc) makes no difference to the possible bore size.

If you have the original block and it had grading on it then its a rough guide but as it was a quick spot check at only a couple of points I would not rely on it these days when boring a block. I am also not sure if they were still grading the blocks by the time the 701m blocks were being used so you may not have any stamping on the front face.

Almost all blocks will take 83.5mm bore. many will go to 84mm and a few to 85 mm

You maximise the life of the block and the number of rebores you can do by centring the rebore in the block casting as the existing bores will not be centred and one side of the bore wall will be thicker than the other. An ultrasonic survey of the block which any good engine machine shop should be able to do these days will determine your current wall thicknesses and determine the offset required when reboring to move the bore towards the centre of the casting as much as desirable with the rebore size your doing

You should be able to get away with a rebore to 83.5mm or +40 thou if your current bore is 83.0 mm provided there is no significant bore damage.

cheers
Rohan

[AlfaLofa]

I've checked the block and it is an LA.

I've searched the internet for a Scottish auto engineering company which lists ultrasonic thickness testing - but found nobody (yet). I'll try 'phoning a few.

Here's a picture of the bores - they look good except for No2 which shows corrosion about 3 inches below the block face.

Has any one used one of these:

http://www.ebay.co.uk/itm/GM100-Digital ... 58a77d8226

[rgh0]

The ultrasonic gauge I bought about 10 years ago cost me closer to A$800 so they are sure much cheaper now!!!

Before that I used to pay about A$50 a block to get its thickness tested which was about an hours labour cost so if you can buy a gauge for the cost of one test worth of labour it looks worthwhile!!

The sensor head needs a radius on it to suit what you are measuring if its not flat and a frequency to suit the material being tested. I got two sensor heads the first with a radius and frequency to suit the iron block bores and one with a smaller radius and frequency to suit the alloy head ports as these are the two areas you need to measure thickness as you develop engines.

cheers
Rohan

[Pistacchio sprint 72]

+0.30 gives how many cc?
+0.40 gives how many cc?

thx

[elj221c]

3.20" Stndrd 82.550mm 1558cc
3.26" +0.010 82.804mm 1567
3.27" +0.020 83.058mm 1577
3.28" +0.030 83.312mm 1586
3.29" +0.040 83.566mm 1596

Assuming standard stroke and me inputting into my calculator correctly!

[robertverhey]

Okay I'll have a go....(and happy to be corrected)

Staying metric,

Std bore (grade 1 pistons) is 82.550mm
Std stroke is 72.746mm

So std capacity is 1557.375cc

40 thou ads 1mm to the bore, making it 83.550, giving a capacity of 1595.334cc

30 thou ads 0.75mm to the bore, making it 83.300, giving a capacity of 1585.801cc

[elanman999]

Robert,
If you are going to do things in metric to 3 decimal places then please get your conversion from imperial correct. 40 thou is 1.016mm.
Cheers
John