Removal and rebuilding of a Twincam

[rgh0]

Rohan, I like that flywheel locking tool. Made? or obtained from?

I made it...the first part of the "make" was 50 years ago when I machined up the bar with different sets of teeth which was one of many samples pieces I made when I did a 8 week machining and welding course at the end of my 2nd year of my engineering course - good training for a young aspiring mechanical engineer , sadly they don't do this sort of practical training of young engineers these days.

The second stage of the make was a few years ago when I found my old stash of sample pieces in a box I had forgotten about and set about modifying them for special tools. Had to grind off one tooth to get the teeth on the bar to match near enough the teeth on the flywheel ring gear and drill a hole to mount it

I made a screw driver and hammer both of which which I now use regularly and lots of other pieces. The centralizing tool I use for the crank and front cover came from a threaded large round nut sample I made that only needed a couple of mm machined off the inner and outer diameter to suit the Twin Cam front cover and crank nose.

cheers
Rohan

[rgh0]

Final clean and assembly of the sump baffles.

Installing a new high volume high pressure pump I purchased as a spare a few years ago. The one in the engine at the time of failure suffered serious scoring to the rotor from the metal going through the engine. The pump body was OK and I have a good rotor and shaft from a pump whose body cracked before I learned how to stop that on race engines so i can build a new spare.

Replaced the O-ring as the one from the manufacturer is to small and the covers leak. original O-ring is 3.1 mm diameter (on top) . The depth of the groove for the ring in the body is also 3.1 mm so no compression. The correct O-ring is 3.5 mm. I bought a pack and swap them now on all new pumps

I also did additional staking of the blanking plate in the body where the filter bypass relief valve was fitted in the original pumps. This should prevent the filter being bypassed by the blanking plate coming loose as it did in the last build of this engine allowing metal to circulate and possibly being the cause of the spun rod bearing

Head goes on next!
cheers
Rohan

[gjz30075]

Good info on the O rings. Thanks.

[alan.barker]

Can the "O" Rings used between the Carbs and Head also be used on the Oil Pump.
Alan

[2cams70]

Regarding the oil pump. I've found that you can make up your own High Volume / High pressure pump using genuine Hobourn Eaton (the original supplier to Ford) parts. The rotors in in an early Triumph Herald / Spitfire pump are the same dimensions as the high volume Ford pumps and you can get a quality alloy end plate of the required dimensions from Initracing in the UK. Mix and match a few genuine parts and you can avoid having to buy one of those pattern pumps.

[rgh0]

Can the "O" Rings used between the Carbs and Head also be used on the Oil Pump.
Alan

No they dont match

cheers
Rohan

[rgh0]

Cleaned the block face and positioned the head gasket with one head stud at rear right. Positioned the front cover cork gasket with aviation gasket sealant. 2.5 mm uncompressed thick cork gasket works with 1.8 mm uncompressed head gasket and front cover about 0.3 mm below block face.

Fitted the cam chain tensioner and final clean of the head face

Head on block and rest of head studs fitted. Also fit the 3 front cover bolts before tightening down the head to ensure all are aligned

Head torqued to 65 ft-lbs with ARP lube on the stud nuts and hardened washers under them. I put removable spacers on the right rear and left front washers that need to be flat filed on them to ensure clearance with the right rear cam cap and left front cam thrust flange as they tend to turn with the final tightening. I use a piece of soft iron wire beaten to the right thickness as the spacers.



Cams fitted and clearances checked. Inlets cams fine with no change from bench set up. Exhaust cam clearance close up 0.001 inch for cylinder 2,3 & 4 which is pretty normal in my experience, so changed shims to get clearance back to 0.010 inch.
Fitted bearings and ready to fit cams

I only bolt one cam down at a time and keep pistons half way down the bores while doing all this clearance checking.

Now ready to time the cams and now need to be careful about alignment of both cams and crank while doing this to avoid bending valves

cheers
Rohan

[RichardHawkins]

Rohan,

I am interested in the torque that you are using with the ARP studs. I also used ARP studs, and although I cannot find the torque figure at the moment, my memory is that the torque was higher. Can you explain please, will you be tightening further later in the assembly, have I made an error?

Richard Hawkins

[rgh0]

Hi Richard
No further tightening planned except to a check after its done a few temperature cycles and then a check after the first race meeting

Yes if I recall correctly, the ARB recommended torque was higher but that struck me as a generic recommendation on what the studs could handle as a maximum rather what the Lotus head and block could handle or need.

I decided to stick with the Lotus recommended torques as a compromise for the following reasons.

1. With studs and fine threads and nuts and ARB ultra lube you will develop a significantly higher bolt tension at the same torque compared to the original coarse threaded bolts and with the additional friction of these bolts in the block as they are turned compared to a nut on a stud

2. Going to too high a tension and you risk pulling the studs out of the cast iron block

3. Going to too high a tension and you risk distorting the relatively soft and weak Lotus head.

In practice I get around the right gasket compression and no head gasket problems with the torque I use and have not had any problems with distortion of the head or thread failures, so I am comfortable with what I am doing. I have only built around 4 or 5 engines using the studs to base those observations on and as always my comfort is subject to change if I have a future problem

cheers
Rohan

[rgh0]

Regarding the oil pump. I've found that you can make up your own High Volume / High pressure pump using genuine Hobourn Eaton (the original supplier to Ford) parts. The rotors in in an early Triumph Herald / Spitfire pump are the same dimensions as the high volume Ford pumps and you can get a quality alloy end plate of the required dimensions from Initracing in the UK. Mix and match a few genuine parts and you can avoid having to buy one of those pattern pumps.

The no name HV / HP pumps have a slightly larger diameter shaft so they dont fit into the original oil pump castings ( without reaming the shaft mounting diameter in the body). I must explore the Triumph shafts and rotors and see if they fit in the original pump body casting ( I have a few of these) with the HV end cover ( I have a few of these also)

Thanks for the tip. The Alloy end plate is also interesting as I think the weight of the thicker steel end plate contributes to the pump vibration and body cracking problems above 8000 rpm with the paper mounting gasket which can be solved with using Loctite 518 instead of the paper gasket but anything to reduce the risk worth understanding.

cheers
Rohan

cheers
Rohan

[661]

Can we persuade Miles to add this thread to his 'Building a Twin Cam' book?
Thanks Rohan, most interesting and hopefully useful for me at some point in the future. Haven't braved the engine yet!

[rgh0]

Can we persuade Miles to add this thread to his 'Building a Twin Cam' book?
Thanks Rohan, most interesting and hopefully useful for me at some point in the future. Haven't braved the engine yet!

I always thought Miles book did not address enough some of the interesting challenges in building modified engines or current engines with new reproduction parts

cheers
Rohan

[alan.barker]

The book to go with Miles Wilkin's book in the past for Tuning was by "David Vizard" title "Tuning Twin Cam Fords" printed by "Speedsport"
Alan

[rgh0]

The book to go with Miles Wilkin's book in the past for Tuning was by "David Vizard" title "Tuning Twin Cam Fords" printed by "Speedsport"
Alan

Yes a valuable reference and good information on "hotting up" a twin cam back in the day but modern twin cam development has gone a long way since that was published also.

Apart from what you read here on LotusElan.net there is not much else that's meaningful that is published specifically about Twin Cam development as the people doing it mainly rightfully consider it their commercial secrets so they are deliberately vague and some are just plain wrong Who would have thought you get wrong information on the internet

Listen to the few who talk a bit more about what they have done and can back it up with real world data- e.g. Vegher , "Avro" here, McCoy etc and look at what people like QED and Tony Ingram supply in terms of development parts, to develop an understanding of what's possible and what's needed. I don't agree with everything they all do but I respect their experience and results.

My aim is to do it better and cheaper than all of them and happy to talk about what I do and why Well I keep trying at least .... and made at least some progress in the last 40 years since I blew up my first seriously developed twin cam.

cheers
Rohan

[alan.barker]

Thanks Rohan,
we all like to follow your Twink info and it's nice for you to share it with us.
When i had my first Twink it was a Ford Cortina Twin Cam and i fitted Piper FY2 Cams, polished ports etc myself. The Vizard Book was the only thing i could find in 1974
Alan