Lotus Elan

Another engine rebuild

PostPost by: Sheldo » Tue May 26, 2020 2:01 pm

Started the rebuild of my TC. The pistons and valves had some pretty serious carbon build up. Anything to be concerned about, or is this not uncommon? It had been running pretty good, just developed a significant oil leak between head and block
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PostPost by: benymazz » Tue May 26, 2020 2:32 pm

Check inlet guide clearance. Some carbon buildup is normal especially on the intake since it runs cooler but the intake valve on the right in the second picture looks a little worse than I’m used to seeing. The carbon buildup on the pistons looks more or less normal.

If you find problems on the intakes obviously check the exhaust guides as well, they probably aren’t too far behind.

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PostPost by: Sheldo » Thu May 28, 2020 5:20 pm

Thanks Ben for the reply.
After getting things completely torn down, cleaned up, and being able to look a little closer, things look better than I originally thought. Now the decision---- go back to original or add hp. Dave Bean has sent a list of parts to go 40 over on pistons, new valves and springs to go to 10.5 compression, and .385 cams. Staying with the Strombergs. Gets me another 30 hp ish??? Would appreciate any thoughts or concerns with this set up.
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PostPost by: alan.barker » Fri May 29, 2020 8:48 am

Sheldo,
why are you going to .040" over size. Have you measured the cylinders and how much worn are they.
Also +.030" pistons do exist. For the Cams and road use i would only go as far as Sprint Cams.
With modern fuels i would not look for increasing the comp ratio.
Personal choice of course and after all it's your car.
Alan
Last edited by alan.barker on Fri May 29, 2020 10:18 am, edited 1 time in total.
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PostPost by: rgh0 » Fri May 29, 2020 9:41 am

I would not go for the 300 degree seat to seat duration .385 lift 112 cam. It's an old style low lift long duration hot up cam designed to drop into the standard valve gear. If your going to rev the engine hard and dont mind losing mid range torque it will give a boost at the high end but there are better cams these days

As you are replacing all the valve gear it costs no more to go for a modern short duration high lift cam such as the QED 420 or McCoy .440 lift cam or equivalent from others with the matching springs and valves to accommodate the higher lift. The nearest cam to this approach at Bean is their 114 but that has a bit to long duration at 288 seat to seat and a bit to low lift at 0.413 to match more modern grinds now available

The measuring and fitting to get it right is a little more complex but the result will be far superior with more mid-range toque and higher power before the 6500 rpm limit in a standard engine.

cheers
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PostPost by: Donels » Fri May 29, 2020 6:32 pm

Don’t make the mistake of thinking high power makes a better car. Unless you are racing or doing track days it can make a good car horrible on the road, I know because I’ve done it. Similarly, super grippy tyres can take all the fun out of a road car, again done that.

My advice would be to decide what sort of car you want and what you’re going to do with it........then decide what sort of engine you need.
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PostPost by: benymazz » Fri May 29, 2020 7:51 pm

Sort of stating the obvious here but with a 1600 Twin Cam, if you increase power it comes mostly from one of two places:

1. Making the engine breathe better by increasing port size, valve size, and valve lift, which increases torque at all rpms including high rpms thus giving you higher power
2. Making the engine breathe better by increasing cam duration and modifying cam timing which diminishes torque at low rpms and increases power at high rpms by moving the power band to higher in the rpm range

If you want a engine that is decent to drive around town you want more of #1 and less of #2. If you’re going to be doing more track work and don’t mind compromising some low end drive-ability, you want all of #1 and some degree of #2, depending on how much low end you’re willing to give up.

As to what DBE recommended, one thing caught my attention. I see -.010” main and rod bearings on your list so I’m inferring you’re running on the stock crankshaft. If you have the round-shouldered main bearing caps (I think they were phased out by the time stromberg heads came around but I’m not sure) this may limit how high you can push the rpm limit and thus the peak power.

Unfortunately for you, modding stromberg heads to get more power is something not done too often because of the higher power ceiling of weber heads so you may have less information available to you than others who modify weber heads do. But the same core principles of getting more power that I outlined above still apply, even if the execution may be slightly different

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PostPost by: Sheldo » Fri May 29, 2020 9:14 pm

Thanks everyone for the feedback - it is greatly appreciated. The consensus seems to be that the DB hop-up is not ideal. Sooo.. time to rethink things.
I have the block and head at the machine shop and they were still in siprisingly great condition. So, I think I'll go back to mostly stock. A light honing on the cyls, polish the crank (it is a 6 bolt with rounded caps), clean up the head - go to big valve spec valves and call it good - more of #1 - for now. Spend the resources on the never ending list of other things that need done - starting with the 50 yr old rear suspension.
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PostPost by: Davidb » Sat May 30, 2020 1:55 am

At least fit Sprint spec cams.
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PostPost by: The Veg » Sat May 30, 2020 2:28 am

Between what a previous owner told me and what I've read in the receipts that came with the car, I've surmised that my block is 40-over, and my Stromberg head has been rebuilt to DB 'stage II' spec which I think is roughly equivalent to Big Valve/Sprint, and has been fitted with the 112 cams. I haven't driven it in healthy running condition as yet, but before I pulled the head a couple of months ago it ran stationary very nicely, which I know means nothing. It'll be interesting to see how it does once I can really drive it.
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