1700 Sprint

[crannyr]

I am doing a frame off restoration of my 72 Sprint. I intend to instal a 1700 cc twincam. In the process I will be replacing the chassis with a new Lotus frame properly reenforced. Can someone tell me whether the 1700 (tallblock) will fit in the original mounting locations with clearance of the hood/bonnet? If the motor needs to be lowered for clearance what is the recommended method?

Thanks

Rick

[garyeanderson]

Hi Rick

I have an S2 with a full height 1600 block twin cam in a spyder chassis using the early cam cover (Lotus down each side) and flat bonnet and no problems with the clearance. There is no sound deadener under the bonnet, or any where else for that matter. I don't think Spyder moves the engine location but hopefully someone else will comment.

Gary

[paddy]

Isn't the difference in height only 3 or 4 mm ?

If so, then I don't think there's a big problem. On my S1, with Lotus chassis, raised RH engine mount, Webers, and late "square" airbox, the closest point between engine and bonnet is the front of the front carb (where the fuel strainer access is) and I'd say there's about 6-8mm clearance.

Paddy

[garyeanderson]

Isn't the difference in height only 3 or 4 mm ?

If so, then I don't think there's a big problem. On my S1, with Lotus chassis, raised RH engine mount, Webers, and late "square" airbox, the closest point between engine and bonnet is the front of the front carb (where the fuel strainer access is) and I'd say there's about 6-8mm clearance.

Paddy

Twin cam block height is 7.78 inch or 197.61 mm (full height)

1600 block height is 8.21 inch 208.53 (full height)

Difference is .430 inch or 10.92 mm call it 7/16 on an inch.

Some people use custom pistons and/or rods, sometimes both to use all of the available block height when building up a tall deck twin cam. This elimenates milling .224 inch or nearly 5.7 mm from the face of the block.

[elansprint71]

If you already have the body off or the engine out, this will probably not help.

Before doing my chassis change I was concerned by a couple of star cracks in my bonnet (hood), these were caused by the cam cover. I removed the bonnet and placed a long piece of straight timber across the body directly over the highest points of the cam cover (over the chain), I measured the gap between the timber and the cam cover and wrote it on the timber.

When I fitted up the new chassis, engine and body I placed the timber in position and measured the gaps. I t was about the same, so I packed up the body on the mounting points along the side of the chassis (frame), adding 1/4 in (6mm) at the front progressing down to zero at the back. Then I drilled ad tapped the bolt holes in the front towers, etc, etc.....
As far as I could figure it this was the simplest way to get the correct clearance without arsing about with slotted engine mounts. For the packing material I used 1/8 in Paxolin sheet, any oil-impervious material would do.

Hope this is of some use.

[msd1107]

For a contrarian point of view; why use a tall block with the possible problems?

The Dave Bean catalog lists suitable connecting rods and piston pin heights suitable for a long stroke crank in a standard height TC block.

And this allows you to retain your matching numbers chassis/engine numbers.

I wish I had gone this route when I went long stroke, but my mechanic recommended the tall block, and I wasn't aware of the problems back then. Fortunately, I didn't have interference issues.

David
1968 36/7988

[elancoupe]

For a contrarian point of view; why use a tall block with the possible problems?

The Dave Bean catalog lists suitable connecting rods and piston pin heights suitable for a long stroke crank in a standard height TC block.

.

David
1968 36/7988

+1

I have had a short 1700 in the car for 16 years now.

Interestingly enough, after I fitted a "Big Valve" cover, I had bonnet interference issues, due to the boss on the front edge.

A tall height unit would have certainly have been more problematic in that regard.

[garyeanderson]

For a contrarian point of view; why use a tall block with the possible problems?

The Dave Bean catalog lists suitable connecting rods and piston pin heights suitable for a long stroke crank in a standard height TC block.

And this allows you to retain your matching numbers chassis/engine numbers.

I wish I had gone this route when I went long stroke, but my mechanic recommended the tall block, and I wasn't aware of the problems back then. Fortunately, I didn't have interference issues.

David
1968 36/7988

Hi David

Some folks still have the original block in good condition but just want a bit more power and torque. Why carve up a stock bore "matching numbers" block when you can get a 711 block with good square main caps for reasonable money. Lotus blocks up till 1968 still have those weak round main caps, to build up one of these early blocks will need a bunch more machining than the 711 block The aline bore and square or steel caps will probably cost half of the tall deck block. I understand that there is a bit of carving to be done so the 1600 crankshaft will spin with the rods attached in the 1500 height block. I had a Twin Cam height 1700 and it was a great engine with the Stromberg head or the Weber head that it was sold with. One thing is certain, no one will make a twin cam height blocks in iron again, so use them up and they will be gone. This is just the way I see things, as always its your Elan do as you will

Gary

[cbxbikenut]

I made a 1700 Twin cam using the stock Lotus block utilizing a Ford what was at the time a stock Formula Ford crank and rods. The longer rods were able to be used by having JE Pistons made that had the wrist pin height adjusted for the application. No problem with ring stack or anything except the block had to have a little, but only a little relieving on the block where the rod bolts were trying to pass.

I think JE would still have the info to make up more of the pistons. I wanted a high silicon content piston and they were at the time the only place to offer the proper blank and be willing to make the piston.

The choice is yours.

Cheers,

Herb

[crannyr]

Gentlemen, thanks for the replys and suggestions. As the post was submitted the original engine was out and the body off so no measurements were possible to determine clearances. The Original motor will be restored to 1600 federal spec for future install in the car as it is unmodified in any way from "showroom" and will be refurbished to that condition over time. As I already have a 1700 tall block finished and ready to install I plan to use this motor for a period of a year or two (because it will go faster).
As an aside, for those in the Northeast of New England. I have a reasonable sound Elan chassis that I will give away to anyone that will pick in up near Worcester, MA. Appears straight with no damage or significant rust other than the lower front cross member which needs rust repair. If interested email me thru this site.
Agian thanks to all for the support.