Lotus Elan

Crankshaft limits ?

PostPost by: cabc26b » Sun Mar 15, 2009 8:22 pm

I am getting around to the engine for the S1 - At the moment i have decided NOT to rebuilt the original to the car motor but instead use an SE weber head motor that I have - This is not going to be an all out race car, so the head configuration I am planning to use will peak at about 7200-7500 RPM.

My recollection of the iron crank ( I have little experience here as i have always run 8 counter weight steel items ) is that this may be beyond it's comfort level to run it up there -

any advice ?

What are the FIA implications ? do they allow the stock pattern steel cranks ? I am staying with FIA regs for the top end so thought it might be advantageous to have a universally accepted motor .

Thanks

George
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PostPost by: rgh0 » Sun Mar 15, 2009 9:58 pm

7200 to 7500 rpm is certainly at the limit for a stock bottom end with a cast iron crank and 125E rods even one that has been prepared with careful balancing, light weight forged pistons, ARB rod bolts, lightening and shot peening of rods and shot peening and nitriding of the crank. You want to have a good rev limiter to make sure you don't exceed this sort of limit as going above 7500 rpm is almost a guarantee of quick failure.

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PostPost by: Dag-Henning » Mon Mar 16, 2009 1:53 pm

George, in addition to what Rohan says, FIA accept steel crank in EN 19 , to the old pattern. ( 4-bolt ) Regulations say nothing abt. number of dowels, so you will want to have four of those as well.
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PostPost by: cabc26b » Tue Mar 17, 2009 3:09 pm

Thanks Dag and Rohan -

One conclusion so far is that the stock 125E crank is not in this engines future. Looks like steel for the material. now what does it look like ? I can't say as I am disposed to build a 4-bolt rope seal at the moment , maybe later with a spare date correct block I have.

Does any one have experience with the EN19 stock pattern cranks ? In the past I have used the 8-counterweight units and loved the smooth spin and knowledge that you had extra rev's in hand if needed. The difference in cost looks to be about $500 or 300 units of an old world currency

I recall that Gary asking for references on a steel crank MFG I also noticed on UK ebay that IK Engineering has steel units at an attractive price ( US made !) , does any one have experience with IKE ( are these the same ones as Gary mentioned in a post I can't lay my hands on )

- New but related question - What is the forums view on using a long-rod ( BD length) on the 72.5mm stroke, I knows it free displacement but also understand that it takes away in another area and can't recall where ?
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PostPost by: msd1107 » Tue Mar 17, 2009 6:18 pm

See the enclosed article on the effect of rod/stroke ratio on the theoretical volumetric efficiency on an IC engine.

Since the crankshaft cetreline to block deck height remains unchanged, changing rod length involves moving the small end bore up or down in the piston.

Depending on the details of manufacture, the longer rod will be heavier and less rigid. The shorter rod will have slightly greater secondary out of balance forces. The G loadings at TDC will be slightly greater. The piston side thrust will be slightly greater.

Within the range of rod lengths available, the changes in any one variable probably are in the low single digit percentage range.

And rod length has no effect on displacement.

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PostPost by: msd1107 » Tue Mar 17, 2009 11:22 pm

Oh, I spoke too soon. The statement that rod length has no effect on displacement is true only for a non-offset crankshaft or piston pin.

At the extremes (long connecting rod, large crank offset), the engine can gain more than double in capacity compared with a non-offset crankshaft. All this is precious information, I am sure. :twisted:

See the attached spreadsheet.

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PostPost by: rgh0 » Wed Mar 18, 2009 7:24 am

I have always used 4 counterweight forged Datsun L16 cranks for my race engines as this is a much cheaper route in Australia than the alrenatives availalble. I have never seen any signficant difference in vibration or performance of these engines versus the 8 counterweight racing crank engines and thus never seen any strong drivers to go down this path at the increased cost.

cheers
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PostPost by: Dag-Henning » Wed Mar 18, 2009 7:50 am

George, I have been racing with the 4 bolt/4dowel EN19 crank from Farndon,and I am very happy with that. Of course the rope seal is what it is, but under FIA rules, you have no option. The crank is normally safe to far above 8000 rpms, but I have no need for more than 7800-7900.
Under the same rules, I use the Farndon steel rods to the old pattern ( "GAF" ) with ARP bolts. They have to be std. length, as this is what is homologated. Logging abt. 4 hrs of race-time a year, I ought to have an engine for at least 5 years, if all the other parts hold together...
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PostPost by: elandoc » Mon Mar 30, 2009 12:29 pm

Hi Rohan,

Interesting about the limits of the std bottom end. I'm going to Bathurst next week (sorry, won't make Lotus 2009) and have just spoken with a fellow club member who swears black and blue that his crank and rods are std (albeit balanced). He revs to 8000 through the gears and 7500 in top. He's also DRIVING his S1 Elan from Brisbane to Bathurst, competing all weekend, and driving back again! He's just put in a 3.5 diff for Conrod.

I've got a fancy-dancy steel crank that the PO put in at great expense (circa $10,000) by a British mob called Gordon Allen - I've never heard of them, but it's been in the car for 16 years now without a problem, so it must be good! The rods are CNC machined H pattern - done in 2001 by a V8 Supercar team who were rebuilding the engine for me. Incidentally, they used a bottom end balancer that was an order on magnitude better than what's commonly available, and the difference was immediate - the bloody thing revved like a jet engine, without any vibration, and 190 bhp on the dyno (1700cc). Anyway, useful horsepower peaks between 7000 and 7500, but with my 3.7 diff, I'll be turning up the limiter to 8000 for Conrod - if I can keep it on the track at that speed.

BTW, are Dorians being used at Winton for Lotus 2009? I need to borrow one for Bathurst, but not off someone who's going, if they're being used.

Cheers

Patrick
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85 Ferrari 308 GTSi QV
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PostPost by: rgh0 » Tue Mar 31, 2009 7:28 am

Hi Patrick

I am sure Bathurst will be a blast

Anyone using 7500 - 8000 rpm on the standard Crank and Rods will suffer a failure sooner rather than later IMHO - and at Bathurst they dont call it conrod straight for nothing. In Victoria most of the failures I have seen occur at Phillip Island where the long straight with a down hill at the end third encourages lots of revs for a sustained period.

If you are careful and only briefly go above 7500 the engine may last a while so a plan of 8000 in the gears and 7500 in top may help delay the inevitable especially if your tach reads a little high.

The Lotus 2009 entry form asked for Dorian numbers so I presume they are using them for people who have them. But you could check with the organisers to confirm and if not then I presume you may be able to pick one up from some of the Queenslanders going - otherwise I guess it rent one - they are normally aviable to rent at most meetings, you need to find if they are doing it at Bathurst and book one

cheers.
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PostPost by: elandoc » Mon Apr 13, 2009 4:56 am

Hi Rohan,

FYI, got back from Bathurst early. On the first sighting lap, behind a pacecar, got to the hill in Conrod and the engine let go. Not sure of revs, but certainly way under 7000, as I was only tootling around. It appears that No.2 conrod needed to step out for some air. After taking every precaution in the world and spending a million dollars, this happens. It'll be a few days before I get it stripped down, so I shall neither speculate, nor apportion blame until then - feeling fairly gutted.

How was Winton?

Patrick
67 S3 DHC - The world's most expensive Elan
64 Morris Cooper S (now sold)
85 Ferrari 308 GTSi QV
79 Ferrari 400i
68 Lotus Europa S2 (in boxes - wanna buy it?)
50 Riley 21/2 Litre (now sold)
65 Lotus Elan S2 (in boxes, soon to be a lightweight)
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PostPost by: rgh0 » Mon Apr 13, 2009 7:47 am

Hi Patrick

Sorry to hear you had problems. Be interested to see what the diagnosis is of the cause when you get it apart.

I see Mike got his Seven up to 7th in the over 2 litre sports car class once he got used to hte track. The organisers obviously thought he was to quick for the under 2 litre class with his little 1600 cc twink.

Had a great time at Winton had to work hard to stay ahead of a 1800cc Gordini Europa and a few Elises. The 350 HP Mackie Exige was awsome to watch go by as well. The dinners and concours and red wine was not bad either !!!!

cheers
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PostPost by: cabc26b » Tue Apr 14, 2009 11:50 pm

Patrick,

Sorry to hear about your bad luck. Please post back with the finding after the post mortem -

Back to bottom end -
down to two options ( have thrown out billet and stock iron) .

Leading candidate - Scat 77mm crank
Second place en40 forged crank 72.5 -

Was thinking about using stock 125E rods but preped. also thought about cosworth steel rods but have come up short need one ( 1) to make a set - in the past I have use the cosworth steel , farndon steel and Carillo's but this is not a racecar and engine is suppose to be done making power at 7200 or so not sure i need to spend the money on trick rods.

any experience out there with SCAT cranks ? opinions on running the stock rods in combo with ?

Thanks guys,

George
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PostPost by: elandoc » Wed Apr 15, 2009 11:03 am

Hi Guys,

Just completed the post mortem. Despite rejecting two other blocks and ultrasounding this one (it was also a XXXX casting - supposedly with thicker walls and more Chromium), it appears No. 2 cylinder collapsed, probably at aroung TDC, and caught the piston on the down stroke, tearing out the gudgion pin, breaking the CNC machined H beam rod in half, which flung around, destroying the jackshaft, the distributor drive, the oil pump drive, holing the block and the sump. Bits of metal then jammed No. 1 and bent that rod, and the piston slammed into the head, bent the valves and broke the buckets.

The crank is very strong, but I'll have it checked for straightness - it'll be out of balance because the (eight) counterweights were gouged and shot peaned by bits of dying engine, and I guess the head can be repaired - everything else is junk.

I just don't know how I can ever trust another second hand part, and I'm not sure where to source another block from - maybe I should put a BDT alloy one in?

Just going to lick my wounds for a while...

Patrick
67 S3 DHC - The world's most expensive Elan
64 Morris Cooper S (now sold)
85 Ferrari 308 GTSi QV
79 Ferrari 400i
68 Lotus Europa S2 (in boxes - wanna buy it?)
50 Riley 21/2 Litre (now sold)
65 Lotus Elan S2 (in boxes, soon to be a lightweight)
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PostPost by: garyeanderson » Wed Apr 15, 2009 11:19 am

Hi Patrick

As other s have said, condolences on the engine. I am not sure what you are referring to when you say XXXX casting. I have been around a little and this term doesn't ring a bell. What it the casting number (xxx E 6015) and date code, I assume 1500/twin cam height. What bore? , did any of the cylinders have liners?
Thanks Gary

elandoc wrote:Hi Guys,

Just completed the post mortem. Despite rejecting two other blocks and ultrasounding this one (it was also a XXXX casting - supposedly with thicker walls and more Chromium), it appears No. 2 cylinder collapsed, probably at aroung TDC, and caught the piston on the down stroke, tearing out the gudgion pin, breaking the CNC machined H beam rod in half, which flung around, destroying the jackshaft, the distributor drive, the oil pump drive, holing the block and the sump. Bits of metal then jammed No. 1 and bent that rod, and the piston slammed into the head, bent the valves and broke the buckets.

The crank is very strong, but I'll have it checked for straightness - it'll be out of balance because the (eight) counterweights were gouged and shot peaned by bits of dying engine, and I guess the head can be repaired - everything else is junk.

I just don't know how I can ever trust another second hand part, and I'm not sure where to source another block from - maybe I should put a BDT alloy one in?

Just going to lick my wounds for a while...

Patrick
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