Lotus Twincam Engine Modifications

[Barney]

A labour of love!
Thank you for your efforts.

Steve

[rgh0]

I have finished Chapter 6 on cam and valve train selection.

Chapter 6 Lotus Twincam Modifications.pdf

(1.46 MiB) Downloaded 394 times

Now working on block and head modifications but it may be a little while till these are completed. I need to get back in the garage as after my recent Phillip Island Historic races Ii have a whirring sound from the clutch when its depressed. Sounds like a throwout bearing which would surprise me as it is relatively new and not one of the dodgy noname ones. Anyhow the engine needs to comeout to investigate

cheers
Rohan

[UAB807F]

Wow. What an excellent article/chapter, loads of detail and easily digestible for someone like me who is interested but only "think" I know stuff. That's one of the best descriptions I've read on how cams work/are selected.

These really need preserving somewhere (wiki, sticky topic ?) as it's just so easy to lose tech stuff like this in a general thread a couple of years down the line.

Thanks again for all your work and sharing it with us. Best of luck with the clutch....

Brian

[rgh0]

When I finish all 10 chapters I will talk to Jeff about including it in the wiki

cheers
Rohan

[661]

I have finished Chapter 6 on cam and valve train selection.

Chapter 6 Lotus Twincam Modifications.pdf

Now working on block and head modifications but it may be a little while till these are completed. I need to get back in the garage as after my recent Phillip Island Historic races Ii have a whirring sound from the clutch when its depressed. Sounds like a throwout bearing which would surprise me as it is relatively new and not one of the dodgy noname ones. Anyhow the engine needs to comeout to investigate

cheers
Rohan

Is it a twin plate clutch?

[pharriso]

Wow, thank you Rohan for capturing & sharing your vast knowledge of twin cams!

[rgh0]

I have finished Chapter 6 on cam and valve train selection.

Chapter 6 Lotus Twincam Modifications.pdf

Now working on block and head modifications but it may be a little while till these are completed. I need to get back in the garage as after my recent Phillip Island Historic races Ii have a whirring sound from the clutch when its depressed. Sounds like a throwout bearing which would surprise me as it is relatively new and not one of the dodgy noname ones. Anyhow the engine needs to comeout to investigate

cheers
Rohan

Is it a twin plate clutch?

Its a single plate AP pressure plate and execdy heavy duty clutch plate. Everything works and feels fine apart from the wirring sound when depressed

[661]

I have finished Chapter 6 on cam and valve train selection.

Chapter 6 Lotus Twincam Modifications.pdf

Now working on block and head modifications but it may be a little while till these are completed. I need to get back in the garage as after my recent Phillip Island Historic races Ii have a whirring sound from the clutch when its depressed. Sounds like a throwout bearing which would surprise me as it is relatively new and not one of the dodgy noname ones. Anyhow the engine needs to comeout to investigate

cheers
Rohan

Is it a twin plate clutch?

The reason I ask is that on swapping to a twin plate clutch mine makes whirry noises on depression


Its a single plate AP pressure plate and execdy heavy duty clutch plate. Everything works and feels fine apart from the wirring sound when depressed

[rgh0]

Just completed the 7th chapter on block modifications see below. Now startting on the head modifications chapter

Chapter 7 Lotus Twincam Modifications.pdf

(1.08 MiB) Downloaded 317 times

Writing progress has been slow as I have been busy since the Pphillip Island race meeting pulling apart the Elans engine due to coolant loss and clutch wirring noise when disengaging the clutch.

Discovered I had cracked the bore in no 2 cylinder causing the coolant loss. This block is one of two I use in my competition engines and I have been using it in racing about 50% of the time for the last 30 years. So at some time they all give up! Now accelerating the rebuild of my spare race engine. Also going on some travel for a couple of months in a few weeks time so getting a new replacement block prepared for my other race engine will have to wait until i am back. Lucky i have a lot of spare blocks but i need to select a good one and get it line bored for new steel caps and bored for 83.5mm to suit my race class 1600cc capacity limits

The clutch noise was due to a lot of clutch disk wear material getting into the the pilot bearing causing it to sieze up. The clutch had totally worn out in about 10% of the time normally in my race engines. I need to talk further to my local clutch specialist about why that was the case !

cheers
Rohan

[fotsyr]

I had a very large and well repected race engine building shop try to advise me that 50thou valve shims were accetable for valve clearance. I disagreed.
Very informative write up.

chris

[LCRJ]

Hi Rohan,
I find your articles very informative and I am learning a lot.
I have a question for engine building,
As a reference value,
What is the maximum rpm allowed with Fandon (QED) forged EN19 steel crankshafts (6bolts) and a square steel main bearing cap bottom? Can 8000+ rpm be acceptable?
We would like to use this part as a base from which to choose other components.
The application is for fast road use and a few times a year on the track, not a race engine.
Best regards,
Hiro

[rgh0]

I would ask Fardon what they recommend as a limit, I have no personal experience with this crank but it should be good for 8000 rpm with square cast iron main caps and suitable light rods and forged pistons.

Here is a link that talks about using the crank at 7900 rpm from a forum member

viewtopic.php?f=12&t=18020

cheers
Rohan

[LCRJ]

Thank you for your prompt information and the link.
Is it a bit risky to use 125E rods + forged pistons based on the crank?
If so, I would consider forged rods.
I think it is important to combine the quality of each component used.
Do you have a priority regarding the crank, rods and pistons?
Thank you.
Hiro

[rgh0]

It really depends on your intended use. The problem with 125E rods is that they are heavy which puts higher loads on the block and crank. The 125E rod strength above about 7500 rpm is also questionable. As I said in my write up if building a road engine that may be used to 7500 rpm occasionaly you could do it with forged pistons, steel crank such as the Fardon EN19 and properly prepared 125E rods. However I personally would build as light and strong a set of Pistons and Rods as my budget could afford

cheers
Rohan

[USA64]

Being a nonracing American, anything above 5,000 RPM sets my teeth on edge!