Removal and rebuilding of a Twincam

[RichardHawkins]

Rohan,

Thanks for the reply on ARP head studs. I have only tightened the studs to the gasket manufacturers torque, “Adjusa” which is in between the Lotus and the ARP numbers. I still have not found my notes on the actual number. Should I reduce and retighten to your setting? My engine has not run yet. I got no real help from ARP, they did not want to deviate from their published data.

Richard Hawkins

[rgh0]

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

Yes it was the first Twincam book I bought also and it was about then in 1974 that I got it also when I first got my Elan

cheers
Rohan

[rgh0]

Rohan,

Thanks for the reply on ARP head studs. I have only tightened the studs to the gasket manufacturers torque, “Adjusa” which is in between the Lotus and the ARP numbers. I still have not found my notes on the actual number. Should I reduce and retighten to your setting? My engine has not run yet. I got no real help from ARP, they did not want to deviate from their published data.

Richard Hawkins

I would leave it where it is. Having tightened and compressed the gasket always risky to lessen the compression and since the block threads are Ok and you achieved the torque and tension you did the head is also OK so no real reason for concern.

cheers
Rohan

[RichardHawkins]

Rohan,

Thanks again, you have set my mind at rest.

[2cams70]

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

Further to this pictures of Triumph Oil Pump versus Ford oil pump and wider Initracing end cover attached. The Triumph rotors are a perfect fit. You can either shorten the Triumph drive shaft or press it out and just use the Triumph rotors on the Ford shaft. Beware there are a couple of different rotor widths used with the Triumph pumps. You need the smallest width rotors from the early cast iron bodied Triumph pump (950 -1300cc Herald/Spitfire engine) unless you are willing to have the wider width rotors from the later Triumph pumps machined down to fit.

Believe it or not Triumph had a problem with oil surge in corners with their setup even on road cars. Their engineering solution - increase the width of the pump rotors to decrease the recovery from surge time!!! Their small width rotors are equivalent to the Ford high volume design and the "improved" later pumps have even wider width rotors again.

[rgh0]

Cam clearances set right, so now to set the cams at the approximate TDC position with lobes pointing inwards on No4 and then rotate the crank to the TDC position.

I check the crank TDC using a dial gauge down the plug hole and set the degree disk versus the pointer to TDC and also check the crank pulley marker versus the front cover, TDC mark, which was all OK

For TDC of the cams the lobes on No4 are pointing inwards and just lifting the valve off their seats, This has No 4 at TDC on exhaust stroke and No1 at TDC on compression stroke. I check the cams position accuracy from the lift at TDC numbers for the cams. These are nominal numbers and depend on the cam final timing but for chain and sprocket connection are close enough.

McCoy 0.440 lift cam on ex. 285 degree seat to seat at 110 MOP, lift at TDC = 0.128 inch
McCoy 0.460 lift cam on in. 300 degree seat to seat at 100 MOP, lift at TDC = 0.200 inch

Fit the chain and sprockets which is always challenging as the sprockets and chain and drive pegs on the cams never seem to line up. I do the exhaust first making sure the chain to the crank it tight and then fit the Inlet making sure the chain between the exhaust and inlet is tight. Then fit and tension the chain slack with the adjuster. I use a bit of tape to keep the chain in the crank sprocket while fitting the cam sprockets. Adjustable sprockets make this easier and you can play with cam versus chain position by a few degrees if needed to get the cam drive peg to line up initially so the sprockets can be fitted on the hubs.

I fine tune the cam position to my desired timing of 106 ATDC MOP for inlet and 108 BTDC MOP for exhaust by tapping the cam versus the sprocket with the adjustable timing bolts loose. A long process as MOP needs to be measured using a calculated midway point between to the same lift with the crank rotated clockwise when checking so the chain tension is correct and then tightening the adjustable sprocket bolts. Long but much quicker than using offset dowels where the sprocket needs to be removed for each dowel change to get final timing of each cam.

Cams timed and all the bolts torqued. Next is final assembly of sump and oil pump and cam cover.

cheers
Rohan

[nmauduit]

Cam clearances set right, so now to set the cams at the approximate TDC position with lobes pointing inwards on No4 and then rotate the crank to the TDC position.

McCoy 0.440 lift cam on ex. 285 degree seat to seat at 110 MOP, lift at TDC = 0.128 inch
McCoy 0.460 lift cam on in. 300 degree seat to seat at 100 MOP, lift at TDC = 0.200 inch

I fine tune the cam position to my desired timing of 106 ATDC MOP for inlet and 108 BTDC MOP for exhaust by tapping the cam versus the sprocket with the adjustable timing bolts loose.

Thank you for sharing your racing secrets Rohan !

did you experiment on the track or dyno to come up with your personal timing, or only simulations maybe ? would you comment on the expected effect (and use conditions if need be, ignition timing or fuel requirements etc...) with respect to the manufacturer specs ?

[rgh0]

Fitted the oil pick up next. With the 120E blocks a screw in pick up is used, which sits centrally to match the sump baffles. Much easier to fit than the later press in pick up and better as not biased to the RH side. The one used is the type without the ferrule that fits in the end, you need to ensure you use the ferrule with the shorter ferrule style nut pickup. I have fitted the locking tab washer but Loctite is a good alternative.

Then test fit the sump gaskets. They normally need a little trimming, with the semi circular gaskets to long and the tabs in the flat gaskets where they fit below the semi circular gaskets to wide.

Aviation gasket sealant on the block side and fit the gaskets then the same on the sump side. Let the sealant go tacky to stop the gasket moving when compressed so no rush and and I clean all the sump bolts while waiting and then fit the sump. Socket head cap screws are easiest to fit and re-tension later. I use longer ones in the alloy end covers through bolt holes to ensure full engagement , seen to many stripped front cover and rear seal bolt holes .

Then fit sump and compress down with the bolts to nip up the gaskets. I Make sure the two semi circular gaskets compress evenly as the sump is bolted down. I lightly compress the gasket and then will tighten it down further next day.

cheers
Rohan

[rgh0]

Cam clearances set right, so now to set the cams at the approximate TDC position with lobes pointing inwards on No4 and then rotate the crank to the TDC position.

McCoy 0.440 lift cam on ex. 285 degree seat to seat at 110 MOP, lift at TDC = 0.128 inch
McCoy 0.460 lift cam on in. 300 degree seat to seat at 100 MOP, lift at TDC = 0.200 inch

I fine tune the cam position to my desired timing of 106 ATDC MOP for inlet and 108 BTDC MOP for exhaust by tapping the cam versus the sprocket with the adjustable timing bolts loose.

Thank you for sharing your racing secrets Rohan !

did you experiment on the track or dyno to come up with your personal timing, or only simulations maybe ? would you comment on the expected effect (and use conditions if need be, ignition timing or fuel requirements etc...) with respect to the manufacturer specs ?

The cams and timing I use is the result of evolution of my competition engines over many years based on with lots of dyno tests, track time, simulations and discussions with people like John McCoy.

Really high lift ( 0.48 to 0.50) cams require a long duration of around 320 degrees seat to seat to get that lift which moves the power band up to high and to narrow for an Elan unless you have a very light one and want to change diffs for every circuit. I have found a shorter duration cam suits my heavier standard weight Elan as required by my production sports racing class and my desire not to change diffs

Shorter duration limits lift so I have explored what are the highest lift cams in the 285 to 300 degree seat to seat range to maintain midrange torque with good top end power. In the end a 300 degree inlet cam and 285 degree exhaust appears to be the best for me.

John McCoys cams have the best combination of high lift and short duration I have found matching my requirements and this produces the best outcome in terms of simulation results and dyno results and track lap times.


My development and experimentation is certainly not exhaustive but its produced a very tractable 180+ hp 1600cc twin cam running on 98 Octane pump unleaded for competition use. Not really a road engine with the 38 mm choke 45 Weber's but I have a 36mm choke set up that only looses a few HP and does not bog down at low revs compared to the 38 mm chokes. I will use on this specification engine when I retire from racing and want more of a road car.

I will post more on the rest of the engine setup as I reinstall in the car and set it up.

cheers
Rohan

[rgh0]

Now time to fit the cam cover and oil pump to complete the engine build ! its been a long journey

I fit the oil pump using Loctite 518 to seal. I found using the standard paper gasket resulted in the pump bolt flanges cracking due to vibration at 8000 rpm+ revs. The extra weight of the HV pump rotors and end cover probably make this worse

Fitting the cam cover I decide to use new D rubber seals. The old ones had gone hard and shrunk so time for some new ones. New on right old on left

Fitted the cam cover like to sump except only put aviation sealant on the head side and put a smear of oil on the cover side so I can remove the cam cover without disturbing the gasket. I nip the cover down to slightly compress the gasket and will tighten a little more tomorrow

So engine is finished and ready to go back into car finally . I touched up the block paint and enjoyed the end product. I hope it runs as well as it looks

One of the things I noticed while doing the final block paint was that there is a screwed in blanking panel in the right hand side engine mount showing in this casting - is this where the "L" block letter was fixed for Lotus blocks? - same moulds just a letter screwed in ? - this is consistent with all my measurements

cheers
Rohan

[alan.barker]

Rohan,
Have you a Breather in the front of the Cam Cover.
Alan

[rgh0]

Rohan,
Have you a Breather in the front of the Cam Cover.
Alan

Yes breather in centre of cam cover that vents to a TTR fibreglass catch tank moulded to fit in the recess in the body moulding just in front of the LH footwell. You can just see the catch tank in the photo.

You loose the original vent system with the McCoy head conversion as its machined off to remove the Stromberg inlets and bolt on the Weber inlet so you need a new one, Many racers fit this style breather even if having the original style breather also

Picture from the engine removal about 6 month ago ... time flies when you're having fun

cheers
Rohan

[baileyman]

I may have had some serendipity on the breather. I cobbled together a breather tube that already had an elbow, so I rotated my fitting to near vertical to get the tube angling to the side.

I notice I get very little oil in the tank. Yet when I first started the the engine, with the breather pointing horizontal, with no hose, oil spewed out covering everything. What the?

So I posit that it may be the vertical fitting orientation that prevents the spew into the tank. It may be that that little bit of uphill gradient is hard for the crankcase pressure to lift the oil over, acting as a separator.

Perhaps if that is true, then adding more vertical would be even better. So perhaps the breather out should be located not in the valve cover but in the front cover further down, allowing for more vertical. And a bulge in the tube up might help even more to cause drops to precipitate.

John

[661]

I may have had some serendipity on the breather. I cobbled together a breather tube that already had an elbow, so I rotated my fitting to near vertical to get the tube angling to the side.

I notice I get very little oil in the tank. Yet when I first started the the engine, with the breather pointing horizontal, with no hose, oil spewed out covering everything. What the?

So I posit that it may be the vertical fitting orientation that prevents the spew into the tank. It may be that that little bit of uphill gradient is hard for the crankcase pressure to lift the oil over, acting as a separator.

Perhaps if that is true, then adding more vertical would be even better. So perhaps the breather out should be located not in the valve cover but in the front cover further down, allowing for more vertical. And a bulge in the tube up might help even more to cause drops to precipitate.

John

The TTR front cam cover breathers have an internal angulation to do the same task

[rgh0]

Time to put everything back in the car now.

Engine bay needs cleaning

then new gear box and the prop shaft will go in.

Finally the engine will be fitted. Its simple assembly is the reverse of disassembly

Cleaned engine bay and backbone tunnel

Prop shaft in place to be slid onto the gearbox as its fitted

Gear box lined up on trolley and slid into backbone, Lower lip on gearbox mount goes towards the front. A couple of bolts and a bar holds up the front of the gearbox while the rear mount is bolted to the chassi

Prop shaft connected to diff

Clutch release bearing and arm and slave cylinder in place

Tomorrow engine off the stand and onto trolley to move out and fit next


cheers
Rohan