Lotus Elan

Short block long stroke engine

PostPost by: ill_will » Thu Sep 21, 2023 8:37 pm

The head has 1.6/1.4" valves and is a smaller port version of the SAS race head to suit DCOE 40s (although it will likely be fuel injected in the long term.) Valves and spring packs are from Craig Beck and they look the business.

Cams are Tony Ingram ING-445V which are 0.437" lift, 283 deg seat to seat (248 deg at 0.050".)

I have some vernier pulleys, and one job for the future is to time it up and check clearances. This raises a question: the starting spec for the cams is 106 deg inlet / 109 deg exhaust. I presumably want to check clearances at a less conservative timing to ensure that when we swing the timing on the dyno that I've checked 'worst case'.

That presumably means pulling both cams back towards TDC, but does anyone have any guidance on how much? For example, a margin of 4 deg would I think mean timing the inlet at 102 deg ATDC and the exhaust at 105 deg BTDC.
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PostPost by: rgh0 » Fri Sep 22, 2023 7:59 am

I would expect 106 to 108 degrees for that cam for road use. 102 to 105 would certainly be as far as you would pull it back if looking for top end power in a race engine

I notice in the photo of the head that the plug in the vent chamber is not installed. Dont forget to do it before installing the head.... been there , done that and its not easy to fit with the head on the engine :(


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PostPost by: ill_will » Fri Sep 22, 2023 7:58 pm

Thanks Rohan, that's useful.

I had a similar thought too that a plug was missing when looking at the photo. Is it a freeze plug style steel one normally there? I haven't seen one out before.

Your comment reminded me of forgetting the rubber drain tube the first time I rebuilt a twin cam - a nasty sinking feeling!

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PostPost by: rgh0 » Sat Sep 23, 2023 7:14 am

Yes its the slightly domed dish style that you tap in the centre to flatten it slighly and lock into place. One old heads you can have trouble getting them to lock properly due to damage in the seating area and I have tapped the hole and fitted a threaded plug in that case

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PostPost by: ill_will » Thu Sep 28, 2023 7:41 pm

I've been doing some measuring recently. Hopefully some of this data may be of use to people in future. Sorry about the mix of units. It might not be the most riveting reading though.

First up was cc'ing the pistons. As mentioned previously these are Dave Bean part number 560E0835, made by JE pistons, compression height 1.46". They have a 1.0 mm top ring (coppery colour coated steel?), 1.2mm 2nd ring (cast iron?) and 3-rail oil scraper. They are 3.284" for a 3.287" bore, to give 1700cc with a long stroke 77.6mm crank (DB says 77.6mm in one place but 3.060" which is 77.72mm in another) with standard 125E rods. The bores are very slightly large, measured at 83.50mm using some fancy 3 line contact trigger style bore gauges at work.

I measured the piston cc with crown 5mm down the bore from the deck, as they have a decent sized intruder. With vaseline in the gap round the perimeter of the crown I measured 20.9cc and 20.6cc on two successive measurements, which I think gives an intruder volume of approx 6.63 cc.

0.1cc gives approx 0.02 compression ratio units at this swept volume and target CR of 10.9 ish. I may remeasure the intruder volumes as my technique has improved since then.

The 84mm Cometic CFM gasket is apparently available at 0.043 and 0.059" compressed thickness, which equates to about 6.05 cc or 8.30 cc respectively.

The land volume I haven't measured yet but estimate at about 0.06cc

The crown to deck height should be around 0.3mm giving about 1.64 cc, but here I discovered a bit of a setback, which I'll post about next.

The SAS race ported head gave 42.4 and 42.6 cc on two measurements.

Overall this gives about 43.6cc total vol at TDC, with swept vol of ~425.5 depending on which stroke value you believe, giving a CR of just under 10.8.

Any second pairs of eyes on the above appreciated - thanks!
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PostPost by: ill_will » Thu Sep 28, 2023 7:56 pm

The setback mentioned above needs further checking, but essentially, when I was trying to measure the crown to deck height I did a trial build of the crank and all four pistons, and used a DTI on magnetic base to drop the DTI pin onto the crown in the plane of the gudgeon pin to minimise the impact of piston rock. I noticed that on the number 4 piston this distance was about 0.1 to 0.15mm more than on the number 1 piston.

I took the block to work and used some long verniers to measure the deck to main cap centreline at both ends of the block. Not an ideal tool as it is difficult to get perpendicular to the two planes. But this suggested the same offset. I've ordered a secondhand massive mitutoyo micrometer which should be a bit better for getting parallel to triple check it, but if this pans out I calculate it's equal to a compression ratio difference of about 0.2 from one end to the other, which needs to be fixed.
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PostPost by: ill_will » Fri Sep 29, 2023 4:04 pm

I did some measuring with a 7" micrometer today between the deck and the main cap split line faces, and the deck and sump mounting faces.

Does anyone know if/how tightly toleranced the crank rotation axis is to the plane of the main cap split? I can't see any evidence that the caps have had the mating surfaces ground and the whole thing line bored but can't rule that out. I can't easily pick up the centre of the bore with the equipment I have.

Both sets of measurements show about 2 thou difference laterally and about 3-5 thou axially, such that the number 1 cylinder corner on the jackshaft side appears about 7 thou further from the main cap split plane than the opposite one.

Any suggestions for other checks appreciated.
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PostPost by: promotor » Fri Sep 29, 2023 5:23 pm

ill_will wrote:I did some measuring with a 7" micrometer today between the deck and the main cap split line faces, and the deck and sump mounting faces.

Does anyone know if/how tightly toleranced the crank rotation axis is to the plane of the main cap split? I can't see any evidence that the caps have had the mating surfaces ground and the whole thing line bored but can't rule that out. I can't easily pick up the centre of the bore with the equipment I have.

Both sets of measurements show about 2 thou difference laterally and about 3-5 thou axially, such that the number 1 cylinder corner on the jackshaft side appears about 7 thou further from the main cap split plane than the opposite one.

Any suggestions for other checks appreciated.


Measure from the top of the main bearing bore to the block top face to see if there's any difference there - I appreciate you'll need a ball-end micrometer (ie rounded anvil) for that but you could use a flat anvil micrometer and one ball bearing between anvil and main bearing bore to get around the problem. Will be a little fiddly but you might just make it work. Obviously the ball bearing needs to be unworn and round!
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PostPost by: rgh0 » Fri Sep 29, 2023 9:30 pm

The Ford drawings how a general machined tolerance of +/- 0.030 inch for the 701M block. The 711M block will be the same

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PostPost by: ill_will » Fri Sep 29, 2023 10:01 pm

Thanks, I'll try the ball bearing idea.

And thanks for the tolerance info.

When skimming one of these blocks (or any block for that matter) is there a generally accepted process or tooling for ensuring parallelism to the crank and/or perpendicularity to the bores?
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PostPost by: 2cams70 » Sat Sep 30, 2023 12:07 am

I’d suggest that what you are observing is quite normal. My block was the same and not quite parallel deck face versus crank centerline. It probably has something to do with the sequence of machining operations when the block was manufactured. Didn’t really matter much in the scheme of things because the head face wasn’t exactly parallel with the cam tunnels and presumably the combustion chambers either! At the end of the day unless you are running a 10/10ths race engine it will make bugger all difference. I’d suggest however running a 10.8:1 compression ratio on a road engine is a little on the high side - cam dependent of course.
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PostPost by: promotor » Sat Sep 30, 2023 7:42 am

2cams70 wrote:I’d suggest that what you are observing is quite normal. My block was the same and not quite parallel deck face versus crank centerline. It probably has something to do with the sequence of machining operations when the block was manufactured. Didn’t really matter much in the scheme of things because the head face wasn’t exactly parallel with the cam tunnels and presumably the combustion chambers either! At the end of the day unless you are running a 10/10ths race engine it will make bugger all difference. I’d suggest however running a 10.8:1 compression ratio on a road engine is a little on the high side - cam dependent of course.


I agree with you, it'll not make too much difference. However, 0.006" piston height difference isn't quite in the ball park for even a standard engine, and it's always interesting to find out why though and satisfying to correct if possible.

ill_will wrote:Thanks, I'll try the ball bearing idea.

And thanks for the tolerance info.

When skimming one of these blocks (or any block for that matter) is there a generally accepted process or tooling for ensuring parallelism to the crank and/or perpendicularity to the bores?


The blocks as far as I know used the sump face as the reference point for skimming the block top and those little stepped pedestals on the side of the block at the top sometimes have correction figures stamped into them for original manufacturers use - I'm guessing that signifies main bearing bore alignment / height and how the block top is machined in reference to that and whether any compensation is needed. Not sure if most machine shops nowadays will even pay attention to that.

The difference in piston heights can also be down to tolerance-stack on the rod centres, piston height, crank journal accuracy from centre line together with any machining on the block. I always try to get pistons sat as level to each other as possible at TDC and usually do a test with just one control piston and rod assembly fitted in each bore to see where the difference lies. I found that some con rods that I had re-bushed recently ended up 0.004" difference in length which is out of tolerance as the range is 0.002" on a set. I can't accept that difference either so they didn't get fitted.
Last edited by promotor on Sun Oct 01, 2023 8:00 am, edited 3 times in total.
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PostPost by: HCA » Sat Sep 30, 2023 9:16 am

promotor wrote:The blocks as far as I know used the sump face as the reference point for skimming the block top


Correct. I have a brand new [711] block. The factory 'after finish laydown checks' data sheet show the deck height measured from the sump face. In my case it is 8.329"...
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PostPost by: ill_will » Sat Sep 30, 2023 6:56 pm

I’d suggest that what you are observing is quite normal. My block was the same and not quite parallel deck face versus crank centerline.


I'm not convinced by this. Remember the bulk of the values quoted above are purely measurements of the deck relative to the main split line and sump faces on the block alone, so without the tolerance stack from the crank, pistons and rods buildup.

My gut tells me seeing 5 thou variation relative to the sump face is about 5x what you'd reasonably expect. With in-process probing on a modern machine you could easily hit a tenth of that.

I'd love for someone to show I made a mistake with the CR calcs but seeing just under 10.6CR on one cylinder and 10.8CR on the one at the other end just from the variation of one geometric feature sounds way too high to be comfortable.

I’d suggest however running a 10.8:1 compression ratio on a road engine is a little on the high side - cam dependent of course


It's a fair concern. If I leave the block as-is I'll have a nice test bed for dialling in the optimum CR!

In seriousness though, there is a thicker gasket available if I do have real issues. The cams are pretty aggressive ramps and decent overlap, and I'm planning to run injection which should give a bit more control over mixture. It will also run 98/99 RON. It will be an interesting and hopefully not too expensive experiment.
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PostPost by: ill_will » Sat Sep 30, 2023 7:10 pm

However, 0.006" piston height difference isn't quite in the ball park for even a standard engine, and it's always interesting to find out why though and satisfying to correct if possible.


Yeah, it'd be nice to fix it possible. From the measurements I can do it looks like the sump faces and main split faces both slope approximately the same amount relative to deck, which points at the block not sitting flat on the sump face when it was skimmed. Or a machine with something not set square. Sloppy either way.

I'll make sure to check where all four pistons land once it's built up. Your idea of also checking with a control piston is a nice one. Cheers.
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