Lotus TC question

[Dan Lipperini Jr]

I have the remains of a Lotus Twin Cam here in the shop and need some information. I only have the block, crank and main caps which I took pictures of and have created a link to. http://s31.photobucket.com/albums/c376/w650gb500/Lotus/

My question for all of you TC gurus is about the crank. Can anyone tell me what is so special about it? Steel? Aftermarket? The reason for asking, is a few years ago a fellow racer offered me a decent amount for it sight-unseen after i described it to him. I declined and kept everything just in case a vintage project found its way into the shop. Basically the block has a few cracks/missing pieces on the bottom of the skirts so it will need to be sleeved. The main caps are a heavy machined/billet pieces and stamped 1 thru 5. Definitely HD stuff. The crank is different from others that I have seen in that it has a more machined finish than most and it has a 12 bolt flywheel flange. I did take measurements of the rods, mains and bore but left the paper at the shop and will post them tomorrow night.

Any and all information is greatly appreciated,

Dan

[Chester Carter]

THE L IN BETWEEN THE ENGINE MT. BOLT HOLES INDICATE HD BLOCK USUALLY PREFERRED BY ANYONE PUMPING THE ENGINE. IE MORE MATERIAL TO BORE INTO BEFORE WATER JACKET APPEARS.
NOT SURE BUT THE 701 MAY INDICATE LOTUS BLOOD LINES, CK WITH DAVE BEAN
MAIN CAPS ARE "BILLET" STEEL AFTERMARKET
DON'T RECOGNIZE CRANK EXACTLY BUT LOOKS SIMILIAR TO MY BDD CRANK. IE TOO MANY FLYWHEEL BOLTS, THREADED PLUGS IN THROWS TO SEAL OIL IN ETC. IF THAT IS A BDD CRANK LET ME KNOW. i HAVE "WINDOWED " COMPANION TO THAT COMBINATION HERE AT MY PLACE. CHET CARTER SF REGION NAPA CA.

[bob darcey]

The 701M "L" block was cast specifically for Lotus Twin Cam motors. It is a "middle-height" block (as opposed to a 8.21" "tall deck" or a 7.11" "short deck"); stock spec is 7.78" crank CL to deck, 3.250" bore and 2.864" stroke for 1558cc, with a 4.80" rod length. As mentioned, the "L" blocks were cast thicker and can be bored further, so you probably shouldn't sleeve it until someone decides what configuration to use it in. Not sure of this, but I would think both the block and crank could be used to build a short-stroke Atlantic motor. Can't tell the brand of crank, but the Cosworth cranks I've seen have a different oil hole plug arrangement than this one, so I don't believe it's a Cosworth. A BDD crank would be 3.060" stroke with narrow rod journals (but different configurations can be built); this crank is more likely a 2.864" stroke. Both the block and the crank are desirable pieces.

[Brian]

The machined-all-over nature of the crank tells you it is a billet crank. While I think forged cranks of decent steel are better in general than billet cranks, billet shows that someone built a high end engine back in the day. Since it's not stock at all, you have to measure the crank throw to find out what stroke it is. I have a couple of 82.2 mm stroke cranks at home, so big engines were around back in the day. My "value" for a billet cranks is the $1600 charged by Moldex last time I bought one, top quality and decent delivery. A used billet crank that is not ground undersize and mag's OK is worth about $1,000 to me. You should also look at the rods - stock Lotus TC rods were not the best, and after market rods were the norm for a race engine. The steel main caps are also normal for any race TC, since the main caps were a bit cheesy on the 120E block that this was based on. While the L designation is good, many 120E blocks can be easily used and once the engine mount is on, you can't tell the difference. I've bored regular blocks to 85 mm. What that means is the L block has a high value for those who value authenticity over performance, and a non-L block can be just as good and half the price for a race engine that just has to go fast.

The steel main caps usually mean that the main bearing bores are .015" oversize and need special bearings. Britain West used to have them in stock and may still do. Make sure you replace all the fasteners with ARP or equivalent, particularly the rod bolts. You don't know where they've been...


Brian

[Dan Morrison]

Showing my metalurgical ignorance here, but what is the difference between a billet crank and a forged one? Thanks.

[Brian]

Forged and billet cranks are usually made (for racing) from equivalent grades of high quality steel. A billet is a large chunk of steel, say 300 lbs, and it gets put on a lathe or a mill and all the bits that don't look like a crankshaft are gnawed off of it. The billet of steel has a natural grain, much like the grain in wood but way small - and the flow of the grain of the steel is interrupted as the lathe bit cuts away the unused metal. The interruption of the grain results in a piece that is somewhat weaker that it might otherwise be.

A forged crank starts with a red hot, malleable chunk of about the same kind of steel that is forged by a giant press in a die that sets the grain of the steel into the shape of the crank. When the crank is made into a finished piece, bits of the outside are cut or ground away, but the core of the crank and it's flowing grain remains intact. That means it can be stronger than a billet crank.

The issue as it related to Lotus TC is that Ford stock cranks of the time were wimpy cast iron cranks, the rods were undersized to some degree, and all needed upgrading to be raceable. Many other OEM's had stock cranks of quite decent forged steel and those cranks (and sometimes rods) were very usable up to say 2X stock power output.

Cast iron cranks (OEM Ford) might be lifed at 15 hours in a racing environment and at basically wishful thinking time in a full race environment without lightened flywheels and all of that. I can say from experience that a 7 pound flywheel makes a stock Ford crank quite useful up to 150 hp and 7,000 rpm. Cast steel like the new FFord cranks might be double or three times the life of cast iron, billet might be 10X the life and gain say 2000 to 3000 rpm in the process (and effectively infinite life at 6500 rpm) and forged might be 15X and still better life at very high rpms.

Brian

[Dan Lipperini Jr]

The 12 bolt flywheel flange is what confuses me. Everyone talks of 4 and 6 bolt but not 12. BDA or BDD possibly?

[Dan Morrison]

Brian, Thanks for the tutelage.

[Brian]

4 bolt was stock ford before the FFord Kent - the 120E type engines and earlier. Aftermarket cranks sometimes (usually?) had 6 bolts but on the old flywheel tail flange size (larger than the FFord crank size as I recall), and a couple or so dowels. These had rope seal rather than lip seal rear seals (lip seal is the big round oil seal that rides on the crank flange, rope seal is two pieces of cotton rope that get stuffed into a groove in the oil pan and the rear cover of the engine), used a different seal carrier and oil pan. As soon as the lip seal crank and oil pan and all of that was available, most people switched to having custom cranks ground with that tail flange and bolt pattern, which was 6 bolts and usually one dowel. The bolts back then weren't that strong, so people went to 12 bolts, no dowels, same basic dimensions, and used them in BDX's. After bolts got really strong and easily available from ARP etc (and people learned more about the natural vibration periods of the high rpm variants of these engines, I suspect), I expect that people went back to 6 bolts and a dowel.

So you never know what you will find when you open up a 120E based engine (or a Formula Junior or early FB engine) - big or small crank flange, 4, 6, 8 or 12 bolts, none, one or two dowels, rope or lip seal. The flywheels came in two diameters as well, the stock diameter and one that used a BMC A-series ring gear.

I have a steel 7 lb flywheel that was made by Brabham in 1966 for FB, A-series ring gear size, large flange diameter, 6 bolts and 2 dowels. It was on a 1865cc Martin three valve engine. It used a Porsche Carrerra clutch which was virtually identical to what Tilton invented a few years later. It's now on a 200 hp BMW 2 litre M10 engine...kinda fun!

Brian

[LolaT440]

I know an old timer who has what he calls an AX block. He says it was a special thicker block. It is NOS and still in a crate, mint. He has no idea of the value, if anyone is interested I can pass it on, I doubt he;ll let it go cheap.

[Dan Lipperini Jr]

I was able to take some quick measurements today, let me know what you think.

- On the upper right corner of the front of the block it is stamped LB.

- Rod journals 1.935" or 49.15mm

- Main journals 2.122" or 53.9mm

- Bore 3.2875" or 83.5mm

- Deck height 7.78"

- Stroke 72.75mm and stamped on the crank. Also stamped GAF or possibly G4F?

- One piece rear main seal

[bob darcey]

Dimensions are right for a Twin Cam, .030" overbore. Crank has standard journal sizes.

Here's something worth watching: http://cgi.ebay.com/ebaymotors/L-BLO...QQcmdZViewItem

[Dan Lipperini Jr]

I rec'd some information from across the pond that states the markings, GAF or G4F, on the crank throw indicated its a Farndon Engineering piece. Sounds good, but whether its true I have no idea.

I guess the guy who offered me $1500 for everything wasn't kidding after all!