Lotus Elan

Things to consider when putting a crossflow into a plus 2

PostPost by: Rossco » Tue Dec 27, 2022 7:21 pm

Hello all,

My 1st post! I am looking to temporarily put a 711M 1600 crossflow into my plus 2 while I built up the funds and time (which will no doubt be longer than I hope) to rebuild the existing big valve twincam.

I have a running 711M 6015BA crossflow with bike carbs which I plan to use.

Having used the search function on here it seems a fair amount comes up about using the crossflow bottom end with a twincam head and others have run a crossflow before.

What I am looking for is a list of things I might need to consider, purchase, modify etc.

I realise I will need change the sump on the 1600 crossflow for a front bowl version but what one and could I use the twincam one temporarily? Other things on my possible issues list are dip stick (how/where), oil amount, engine mounts, exhaust, general plumbing and how/where to run a vacuum pick up for the headlights.

Any guidance much appreciated.

Thanks
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PostPost by: HCA » Tue Dec 27, 2022 11:02 pm

Re the sump - what type is your existing engine? If an early type then you need to buy a ‘six bolt’ sump. Allow a budget of maybe £400 ! (Some on ebay are less, but these will be made up and leak badly)

Vacuum for lights? Inlet manifold. Might have to drill a small port though.
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PostPost by: rgh0 » Tue Dec 27, 2022 11:08 pm

A few items to think about

1. Type of clutch assembly and match to the twin cam throwout bearing and carrier.
2. Flywheel ring gear type and matching a starter
3. You can swap the twincam front bowl sump onto a push rod with rear bowl but you will need to also change the oil pick up ( I am assuming your 711m pushrod block has a six bolt crank and you Plus 2 the same)
4. The front bowl pushrod engines had a dip stick in the front timing chain cover so you will need to get one of these
5. You will need new exhaust headers I think the twin cam ones will not fit

cheers
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PostPost by: Rossco » Wed Dec 28, 2022 12:48 am

Thanks,

Just about to lift the twincam engine out so will have a look and compare the flywheel, ring gear, number of bolts etc as suggested. Hopefully the twincam sump can be used. I do also have a 105e which has a front bowl but not sure that will fit?
I have read that the crossflow is 11mm wider than the twincam, not sure if true but presume that will mean making smaller nsr engine mount spacers?

Thinking about using a 12v vac pump (Hella UP28 type) to run the brake servo and headlights. Not sure if possible?
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PostPost by: 2cams70 » Wed Dec 28, 2022 1:29 am

You are best to use the twin cam clutch and flywheel assembly with the crossflow. Assuming it is 6 bolt it will fit OK. The crossflow normally has a different flywheel (heavier) and is designed to work with a smaller diameter clutch and pressure plate. The crossflow pressure plate does not have a release bearing thrust pad. It can be made to work but much easier to just use your twin cam parts. If you are using a front bowl 6 bolt sump be careful what rear oil seal carrier you are going to use. Most likely you'll need the 2730E type (same as twin cam) and not the 711M type. There's different half moon seal groove widths and you need the correct type to correctly match the sump. There weren't too many 711M engines mated to front bowl sumps ex-factory. Most of them went into Escorts and Capris with rear bowls sumps. You'll also need from the Cortina/Capri the front timing cover with dipstick hole as all Escorts had the dipstick at the rear. Yes the 711M block is slightly wider across the engine mounts than the pre-crossflow.

The cross flow is actually a pretty good engine that can cop a lot of abuse and modification. Certainly it's much less trouble than a Twin Cam. Note despite having a pushrod design when fully modified the original Anglia 105E engine was capable of 10,000RPM.
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PostPost by: rgh0 » Wed Dec 28, 2022 2:15 am

I believe a twin cam 6 bolt sump should fit OK on a pushrod 711 block with the later wider groove seal carrier. i dont think the sump seal profile itself changed just the seal carrier groove width to enable fitting of of the rubber seals adopted at the front and rear instead of the earlier narrower cork seals that Lotus stayed with through all of twin cam producton. You will need to get a push rod sump gasket kit when swapping the sump over to the pushrod block.

If you have a front bowl 105E anglia engine then it will probably be a 4 bolt crank unless it has been fitted with the later 6 bolt crank at some time in its history ?
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PostPost by: 2cams70 » Wed Dec 28, 2022 2:55 am

rgh0 wrote:I believe a twin cam 6 bolt sump should fit OK on a pushrod 711 block with the later wider groove seal carrier. i dont think the sump seal profile itself changed just the seal carrier groove width to enable fitting of of the rubber seals adopted at the front and rear instead of the earlier narrower cork seals that Lotus stayed with through all of twin cam producton


The seating area for the rear carrier inside the sump has a centrally located ridge pressed into it that is designed to compress the half moon seal into it's location. If you use a non-matching carrier of incorrect width this ridge might not compress the central area of the half moon seal and will be offset somewhat and you'll risk an oil leak. Always best to use a rear oil seal carrier together with the sump it was originally designed to be paired with. There's more than one type of 6 bolt rear oil seal carrier.

You wouldn't want to use an Anglia sump on anything but an Anglia because the oil capacity is even less than a standard Cortina. All Anglia cranks are 4 bolt. They are three bearing mains with an incredibly short stroke!
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