Lotus Elan

Rebuild

PostPost by: carrierdave » Tue Mar 15, 2005 3:59 pm

Good afternoon all,
I am in the throws of rebuilding an engine around the 711m block and would like to use some type c conrods along with standard 82.3 mm pistons; Therefore I will have the block re sleeved or bored out to suit the pistons.

After reading one of the articles on this site I am aware of the various differences between the block i.e. engine mount on the exhaust and overall height of the block. My question is ? how much (based upon standard pistons) will need to be machined from the top of the block? And then from the engine mount points? The article talks about 12.7mm and half an inch respectively ? Is this accurate?

Another question ? would it be better if I went for the 711M block with a std Ford crank but with lotus rods and pistons? What sort of capacity would I get with the longer stroke or does the lotus and ford crank have the same stroke height?

Any help would be appreciated.

Thanks

David
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PostPost by: Foxie » Tue Mar 15, 2005 5:21 pm

David,

I hope not to be discouraging, but if you at this stage you are asking the difference between the standard Lotus and the standard 711 crank, and have not calculated the final capacity of your design, IMHO you have dived in at the deep end.

The standard Lotus bore is 82.55 mm, 82.3.

Standad Lotus stroke is 72.746mm.

Cross flow stroke is 77.724mm

Cross flow stroke and standard bore will give 1664 cc

The 711 block would not normally require resleeving to safely go to 82.5.

There is no maching required on the engine mounts, just different length spacers.


Whatever combination of crank, rods, and pistons you use you need to know beforehand accurate dimensions for stroke, rod length, piston compression height, and block centreline to deck height. When you have crank assembled in the block, fit a test rod and piston to calculate how much needs to be machined off the deck, bearing in mind that if you have increased the capacity you will need to recover your compression ratio.

You will need a timing case spacer, or new timing case castings (with removeable water pump). This will need to be decked with the block.

Get a copy of Burton catalogue, they explain the calculations required pretty well.
Dave Bean catalogue also has good info.

Hope this helps,

Sean Murray
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PostPost by: carrierdave » Tue Mar 15, 2005 8:32 pm

Hi Sean,
Many thanks for the note, my message was somewhat brief and did not include all of the specific data so your statement of in the deep end was accurate.

The reason for having the block re sleeved is that it currently sits at 85.5mm and I was not too keen on going too far away from standard. (although I may change my mind if I see a good set of pistons).

My intention was to get hold of a standard xflow crank and have it toughened and balanced and then fit to it twin cam rods; would this give rise to a different stroke than the 77.62mm you mentioned? - would it be the 72.7mm of a standard engine?
Therefore I suppose the question is what is the difference in lift height of an xflow crank to that of a twin cam - is it around 5mm or are they the same.

Therefore with a 82.55mm bore on a 711m block, with an xflow crank, standard pistons and twin cam rods I would have a certain deck height; this would then need to be machined to within 10 thou of the piston to get the approx compression ration. Is this correct?

Alternatively I could use the twin cam crank and put it all back as a twin cam setup; obviously I would use the crank sprocket from the twin cam to ensure my timing is correct.

Good point about the spacers - I forgot about those!!

Thanks

David
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PostPost by: lotuselanman » Wed Mar 16, 2005 10:54 am

:P :( :unsure:
Gidday,
Les here calling from Australia.
Stop !!!
Now lets clarify a few items. You are using the 1600cc X-flow block as as a basic item, Yes !!
So if the X-flow block is bored to Std T/C you will have 1658cc, yes !!
By using a x-flow block you increase the cc of the engine by 100cc, ok ?
So, by using the x-flow block, Crank and Con Rods we achieve the above, ok ?
Is that what you are after ?
I await your answer.
See ya, Les.
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PostPost by: types26/36 » Wed Mar 16, 2005 4:08 pm

Dave,
Using a combination of 125e rods with a lotus crank and a 711 block will not work due to the height of the block,length of conrods and piston deck height, the pistons would be too far down the bore.Changing the con rods does not alter the stroke.
You need to use an xflow crank (77.62 stroke) xflow rods and lotus pistons,with 82.55 it will be 1662 cc. The block needs decking by about 5.5 mm so the piston is 0.25 mm below the face, this is worked out by fitting a rod and piston after the rebore. A spacer of approx 5mm is needed if useing the standard front cover again the exact size can only be determined with a "dummy build"
Other point to note, check the head bolts dont bottom after decking, take out the pin in the front main brg cap, use the lotus jackshaft spacer and longer dowel, use the lotus crank sprocket, use a 122 link timing chain and reset the cam timing because of the longer chain. There are some other differences with the 711 like the oil tube return hole, flywheel clutch p.c.d. and ofcourse seal the dip stick hole.
If you need some pics to help mail me.

Regards Brian.
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PostPost by: gjz30075 » Wed Mar 16, 2005 8:15 pm

Dave, why are you bothering with a standard Lotus crank with a 711 block? It doesn't buy you anything unless you can't find a suitable 1500/Lotus block. Is that the issue here?

Greg
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PostPost by: carrierdave » Wed Mar 16, 2005 10:32 pm

Hi Brian and Greg,
Thanks for the note Brian, that was most useful. You hit the nail on the head with your response.

Greg ? Lotus blocks are like rocking horse dung certainly from my limited experience.
The idea of using the 711 block was to keep my car on the road whilst I spent my time building a slightly up rated engine, I know I have obviously too much time on my hands.

Brian, I am running weber 30's, will I need to look at re-jetting the carbs with the added CC?s

Thanks

David
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PostPost by: types26/36 » Fri Mar 18, 2005 4:23 pm

Dave,
Not sure what you mean by "weber 30's" I presume you are refering to the chokes but the short answer is probably, depending where in the world you are as altitude affects the carburation. I would think you would need 32,33, or 34's with jetting based around Sprint specs but this would depend on cams, compression, timing etc.
Regards Brian
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PostPost by: gjz30075 » Fri Mar 18, 2005 5:08 pm

Dave, I understand now.

To keep costs and 'technology' down, you can have the 711 block milled all the way down to a 1500 deck height so you won't have to worry about spacer plates, longer breather tube, chain length, etc. And you can still fit the 711 crank (crossflow) with the proper pistons to get the stroker advantage.

Greg
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PostPost by: types26/36 » Fri Mar 18, 2005 7:39 pm

Greg,
I could be wrong here but decking a 711 down to 1500 height would mean taking off approx 12 mm (1500 is + - 200mm and 711 is + - 212 mm) would a block accept that ? head bolt threads, oil gallery, internal construction ? I have serious doubts, this is possible ? I have never heard of this as an option, do you have first hand experience of it working? :huh:
Regards Brian.
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PostPost by: carrierdave » Sat Mar 19, 2005 12:13 am

Hi Greg and Brian,
From reading the article ?Torquing Technical ? Lotus 1558cc Twin Cam Rebuild? by Martin Lucas in the Engine section of this web site ? It states ?Lastly you can machine the crossflow block to correspond dimensionally to the Lotus Ford ?L? block?.!!!

As you say ? this may have other issues in terms of head bold thread depth, water jacket integrity and oil paths etc?

I have just picked up an old 711M block from Ebay for a ridiculous some of ?1. If you guys can give me some idea of the Twin cam block height I will see if I can get it machined down.

I will then let you know what happened.

Thanks

David
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PostPost by: types26/36 » Sat Mar 19, 2005 3:16 pm

Dave,
As I said in the prevous mail the 1500 (T.C.) is + - 200mm, I would be most interested to find out what happens when you deck it that much but for ?1 I suppose its worth trying. :rolleyes:
Regards Brian
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PostPost by: rgh0 » Sun Mar 20, 2005 12:34 am

The 1500 blocks I have measured that have not been machined as far as I could tell have been in the 197.6mm to 197.8 mm range from centre line of crank to top of block. My understanding is that the top of the water jackets are too close to the top of the block to bring a 711 1600 block down to a 1500 block height but I have never tried to machine one down so it could be incorrect

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PostPost by: pereirac » Sun Mar 20, 2005 8:54 pm

QED do a 711M block to take a twin cam head. It might be worth talking to them?

<a href='http://www.qednet.demon.co.uk/tc/shortwork.htm#1700' target='_blank'>http://www.qednet.demon.co.uk/tc/shortwork.htm#1700</a>

Carl
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PostPost by: carrierdave » Mon Mar 21, 2005 6:35 pm

Thanks Rohen and Carl,
I too have concerns over the amount of steel between the head and the water jackets. As the block only cost me a quid I shall find a machine shop who can give me some advise on it. My other concern would be on the head bolts - I assume that these would need to be cut down to ensure they do not bottom out - Something for the vernier to check!!

I will also give QED a call to find out about the extent of work carried out on the block and crank.

As soon as I have some news I will post the outcome.

Thanks

David
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