twin-cam block

[shaun]

Hi can anybody help,just had my early block reborded to +40 and found the bores are to thin,can i fit my early 4 bolt crank to a 711m crossflow block and use lotus pistons with 125e rods cheers shaun

[paddy]

Have you thought about fitting liners?

Paddy

[gjz30075]

Yes and no. The crank will fit and and you'll need the proper pan and rear seal cover. However, the block is too tall and the piston won't reach the top, and you'll end up with low compression. The timing chain will be too short and the front cover won't reach the head; you'll need a spacer there. The block will need to be milled to the height of your old block. I'd keep looking for a proper block.

Greg Z
'72 Sprint

[aussieelan]

Given your L block is stuffed ... you have a few options available.

This article makes for some good reading and outlines a few options for you.

I don't know the availablilty of L blocks where you are, but here in Oz people think they are like the "holy grail" and charge accordingly. You may be better to stick the remains of your L bottom end under a bench and build up a 711 motor. Based on the costs out here you could build up a 711 for about the same cost as buying a used L block.

[rgh0]

Shaun

How thin is to thin - do you have ultrasonic measurements of wall thickness or just a hole in the wall when the bored the block without measuring how much wall thickness you had remaining?

Many Ford / lotus 1500 blocks will go to 83.5mm ( +40 thou on Lotus stadard 82.5mm) OK. A wall thickness of 3mm is good but you can get away with 2.5mm. You do however normally need to offset bore the block based on wall thickness measurements to centre the larger hole in the casting outside diameter.

Getting another standard 120E or 701M 1500 block is the alternative to building a long stroke motor with a 711M block as they are identical to the L block except for the L on the side. If yours is an early 4 bolt crank motor then it will be just a standard 120E block with the 120E ground off by Lotus anyway.

regards
Rohan

[richardcox_lotus]

Genuine L Blocks in good condition are hard to find here, unless you want to pay big bucks. I would agree that it may be easier to get your existing block relined - I've recently had an old (ebay) block relined back from +40 to standard.

[rgh0]

Relining a 83.5 mm bore back to 82.5mm is practical provided you have enough wall thickness left to support the liner. How much is enough is debatable but I have had a block with around 1.2mm to 1.5 mm wall thickness in the bore fail behind the sleeve and then the sleeve itself crack.

So the block is usable as is at +40 thou if wall thickness 2.5 mm or greater and usable sleeved back to 82.5mm if wall thickness 1.5 mm or greater. If wall thickness now less than 1.5 mm with a 40 thou overbore I would look for another block.

You can supposedly get high strength chrome moly liners that can tolerate a cracked casting behind them at 1mm thickness so any block should be recoverable but I have never tried them and they cost about US$1000 each so its always been easier to find another block so far.

cheers
Rohan