Lotus Elan

711 long stroke crankshaft

PostPost by: seniorchristo » Sat Jun 22, 2019 12:35 am

I have a 711 crankshaft I would like to consider for a 1700 project. Brian Moorcroft says it's capable of 7200rpm when balanced. Others say as little as 6000 rpm is safe. I am installing Bean 114 cams and would like to use an occasional redline of 6500.. What are opinions on the robustness of this crankshaft?
Thanks :)
Chris
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PostPost by: promotor » Sat Jun 22, 2019 7:18 am

Hi Chris,

Perfectly fine to use - would need to be a dynamically balanced bottom end to allow use of the crank at those rev's though.

In case you can't see the thread below you will be interested to know the 711m crank was in an engine that was rolling-roaded up to 7200rpm.
The engine builder is from a well-known engine-building family (Harris Performance Engines / H.P.E.) and the mk2 escort using the engine did a 12.7 second 1/4 mile! That's faster than a lot of Supercars! I've seen the car run and it was phenomenal!

http://www.turbosport.co.uk/showthread.php?t=124971
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PostPost by: seniorchristo » Sat Jun 22, 2019 1:40 pm

Thanks Al
Looks like you're my go to guy for engines and differentials :D . How about gearboxes? I'll be doing one of those soon. Considering rebuilding with Aluminum case and tailshaft.
Later
Chris
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PostPost by: 2cams70 » Sat Jun 22, 2019 2:53 pm

It might be capable of 7,200RPM but for how long? They usually fail due to fatigue. Won't happen immediately but it will happen. 6,500 should be quite safe for a long while though because that's the standard RPM limit. I'd make sure I was running it in a block with square or steel main caps. The more rigid you can make things the better for the crankshaft.

I note that Ford seemed pretty canny in it's design of crankshafts. For the 1600 block we have 2737E cranks for pre uprated (small combustion chamber in head) engines and 711M cranks for (flat type head) engines. The 711M had bigger counterweights compared to the 2737E. Same for the 1500 block. We have the small counterweight crank for the pushrod engine and the large counterweight crank for the LTC.

I suspect the difference in crank counterweight design is something is to do with the different reciprocating masses (piston + conrod weight). Interestingly it seems to be something rarely considered by the aftermarket where cranks and piston/conrods are mixed up every which way without any consideration of this.

For the 1600 block I'm not sure which is better - 2737E crank or 711M? Apart from the difference in counterweight mass they are both physically interchangeable.
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PostPost by: promotor » Sat Jun 22, 2019 7:25 pm

seniorchristo wrote:Thanks Al
Looks like you're my go to guy for engines and differentials :D . How about gearboxes? I'll be doing one of those soon. Considering rebuilding with Aluminum case and tailshaft.
Later
Chris

Ha, no worries! I fiddle with gearboxes too every now and then! You know where I am if you want to message me! :D
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PostPost by: seniorchristo » Sat Jul 06, 2019 1:00 am

Sandy at Quicksilver Race Engines took a look at this crankshaft and said it had been tuftrided. He said he could tell by the coloration. He said a couple of the journals should be polished but otherwise it looked OK. He also said it was only necessary to use a square/steel cap on the center main bearing. Question: Do the drilled holes in the counterweights look like balancing holes from factory or aftermarket? There is also a substantial groove in the rear sealing face that needs repair. Sandy said he has also spaced the seals out by putting a piston ring between seal and cover to move the seal and avoid the score marks. Very interesting :)
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PostPost by: StressCraxx » Sat Jul 06, 2019 2:41 am

seniorchristo wrote:Sandy at Quicksilver Race Engines took a look at this crankshaft and said it had been tuftrided. He said he could tell by the coloration. He said a couple of the journals should be polished but otherwise it looked OK. He also said it was only necessary to use a square/steel cap on the center main bearing. Question: Do the drilled holes in the counterweights look like balancing holes from factory or aftermarket? There is also a substantial groove in the rear sealing face that needs repair. Sandy said he has also spaced the seals out by putting a piston ring between seal and cover to move the seal and avoid the score marks. Very interesting :)


Sandy is one of the sharpest engine builder here in the "Colonies." Ask him for a quote to refurbish it vs. a new cast steel crank. The steel cranks are less likely to fatigue fail between #3&4 throws. I have had two cast iron cranks fail in my Formula Fords. I have not had a failure with the cast steel cranks. The only ones I know that have were subjected to ground strikes from the flywheel.

On edit: If this crank is for a street motor, no worries. You probably won't be spinning it to within an inch of it's life that often.

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PostPost by: 2cams70 » Sat Jul 06, 2019 5:52 am

seniorchristo wrote: He said a couple of the journals should be polished but otherwise it looked OK. He also said it was only necessary to use a square/steel cap on the center main bearing. :)


It's not possible to line bore only one bearing position. 80% of the cost of fitting replacement main caps is in the machining for line boring. Why on earth if that's the case would you fit just one cap? They are usually supplied in sets of 5 in any case. I hate to say this but I don't like your engine builder.
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PostPost by: seniorchristo » Sat Jul 06, 2019 10:14 am

Dan
Thanks for the info. I don't plan to exceed 6500 RPM. What was your rev limit in FF?

2cams,
What Sandy said was that the center main cap could be maybe be "line honed". Burton sells individual caps. Quicksilver has been building FF engines since I was racing them in the mid seventies. I will get more specifics about the center main cap when I next talk to him. Any ideas on the balancing holes?
Thanks, Chris :)
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PostPost by: 2cams70 » Sat Jul 06, 2019 11:05 am

Those holes are quite normal. They are balanced at the factory by drilling holes. Subsequent balancing afterward is also done by drilling holes so it's often not possible to distinguish between those originally done at the factory and those done by someone else afterward. Having said that though I try and always choose crankshafts that aren't riddled with holes. If they are riddled with holes then its obvious that the material density is all over the place and so the factory had problems balancing it originally. I've had one engine that had an odd vibration harmonic just at 4,000RPM and when I pulled it down sure enough I found a crankshaft riddled with deep balancing holes around the center bearing. Subsequent replacement of the crankshaft and a full balance cured it completely. I'd say yours looks to be reasonable in that regard.

As you can imagine in a factory building mass produced engines it's difficult to balance front pulley, crankshaft, flywheel and pressure plate as an assembly together where as in an individual build it's not that hard.

You can usually achieve a better standard of balance doing things this way in an individual build. For me it's always a no brainer to have any engine properly balanced during a rebuild. The cost is minimal in the context of a full rebuild and the benefits well worthwhile.
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PostPost by: StressCraxx » Sat Jul 06, 2019 4:10 pm

seniorchristo wrote:Dan
Thanks for the info. I don't plan to exceed 6500 RPM. What was your rev limit in FF?

Thanks, Chris :)


6850 rpm.

The early Cortina/Kent engine stock redlined at 5000. I think that explains the lower torque value.
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PostPost by: 1owner69Elan » Sat Jul 06, 2019 4:44 pm

I have a SCAT (“essentially a Formula Ford”) crank in my stroked 1700 cc twincam. Engine builder stated a 7K redline for the engine. I have a Pertronix rev limiter set at 6900 to help govern my exuberance.

A street car so not revved to the max all the time. Also, the broad torque curve does not require high revs to capture a torque peak.
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PostPost by: 2cams70 » Sun Jul 07, 2019 3:45 am

StressCraxx wrote:The early Cortina/Kent engine stock redlined at 5000. I think that explains the lower torque value.


Mk1 pre-crossflow 1500GT Cortina's had a tacho with a redline starting at 6,000RPM. Later crossflows in Escorts and suchlike had a redline starting at 6,500RPM.
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PostPost by: StressCraxx » Sun Jul 07, 2019 4:39 am

2cams70 wrote:
StressCraxx wrote:The early Cortina/Kent engine stock redlined at 5000. I think that explains the lower torque value.


Mk1 pre-crossflow 1500GT Cortina's had a tacho with a redline starting at 6,000RPM. Later crossflows in Escorts and suchlike had a redline starting at 6,500RPM.


I stand corrected. I used to commute in a 68 Cortina GT with a co-worker. I thought the tach redlined at 5.
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