New S1B owner

[GavinT]

I'm not understanding the term "Boxed values".

Looking at your spreadsheet, there seems to be marked differences in combustion chamber volumes (head volume).
If you've measured 38.50cc and the stock head is supposed to be 55.67cc, something doesn't seem right to me.

Consider another angle:
The volume contained in a cylinder 76mm dia. x 1.00mm high is 4.54cc.

Given 1.00mm has been skimmed from the head, that's a 4.54cc* reduction in chamber volume.
*Given the combustion chamber is not a full cylindrical shape, the figure would be less than 4.54cc.
Am I missing something?

Some time ago there was discussion about figuring out these volumes. JB had the best and simplest idea IMHO, which, if I recall, amounted to installing the head & gasket, sealing everything with Vaseline, set to TDC and do the burette routine via the spark plug hole. This method should also avoid error stack-up.

Another thought - perhaps a custom thicker gasket might save the day?
I think Richard Mann has thin ones so he might have thicker ones as well. Salv Sacco would be another option.

[314159td]

Consider another angle:
The volume contained in a cylinder 76mm dia. x 1.00mm high is 4.54cc.

Given 1.00mm has been skimmed from the head, that's a 4.54cc* reduction in chamber volume.
*Given the combustion chamber is not a full cylindrical shape, the figure would be less than 4.54cc.
Am I missing something?

"boxed" meaning really more like outlined.

Yep, the guys at work were digging into that. We figure there must be something off with one of those assumptions or the input values as the math itself checks out. Someone got smart and suggested just finding a measured value for an untouched head's volume, because my calculation for that has several potential sources of error (we're thinking a rounded/wrong advertised compression ratio). Just take the delta of the stock head volume versus mine, and machine that amount off of a raised piston 

[jbcollier]

I’ve been meaning to go through your math but haven’t had the time yet.  If a flat top piston is 9.x, there’s no way the raised pistons are bumping it to 13.x.  There’s just not that much extra material.

[314159td]

My math spits out just under 1 cubic inch of material in the raised section of the piston, and that feels right based on the pictures I've seen?
Haven't seen one IRL so that could be off, and probably is if any of the published specs are a few % off.

[kram350kram]

Interesting discussion on CR. Static is one thing, dynamic another. Intake valve closing is the big determining factor on the real compression. Cam timing plays a huge part, so you can get into trouble if you want a streetable engine on pump gas, or even a race engine on racing gas. There are online calculators that can help you out on determine the running compression.
Short story. Friend bought very expensive Kirkham replica Cobra with a new, but never run 302.  We had all the spec’s and parts numbers, except the cam spec card. Also did not know where the cam to crank timing was set. Stored for years, but completed and supposedly ready to go. After initial prep, could not get it to run at all. Not the first time around the block for either of us with these engines. On tear down, come to find out the dynamic compression was about 6.25 to 1. So, wrong cam, cam timed wrong, retarded to apparently run on pump gas? The point is the advertised piston static compression was 10.5 with the heads advertised  cc’ column. That advertised CR really  meant nothing with this cams timing. New cam, more advance, dynamic now at 8.7 to 1. Runs nice on pump gas.

[GavinT]

OK, I think I've figured it out, so correct me if wrong.
I believe the error is in column E where the "Raised piston volume (cc)" is already accounted for in the "Head Volume (cc)".

Also, "Head Gasket Volume (cc)" wasn't included in the calculations for columns B & C, and when you do, the compression ratio seems to come out wrong.
Columns B & C also appear to use different formulae to calculate "Combustion volume (cc)" so I didn't go further down that path.

As a cross check, here's my effort.
My assumptions are contained in column B where I just tweak the "Head Volume (cc)" until I get the "Calculated compression ratio" right.
This establishes the "Head Volume (cc)" which is carried across as a fixed value.

Column C is tweaked similarly via "Raised piston volume (cc)" until "Calculated compression ratio" looks right.
This establishes the "Raised piston volume (cc)" as a fixed value.

Columns D and E are then extrapolated and I've included the "Head Skim allowance (cc)" mentioned in a previous post. I took a stab in the dark and assumed 3.5cc as an estimate of the material removed.
Does that look right?

Hoping this link works.

https://docs.google.com/spreadsheets/d/1c3XQoc8EcwDdMsnPR-BS5--745BCabZZrsURfPMtvwI/edit?usp=sharing

[314159td]

Also, "Head Gasket Volume (cc)" wasn't included in the calculations for columns B & C, and when you do, the compression ratio seems to come out wrong.
Columns B & C also appear to use different formulae to calculate "Combustion volume (cc)" so I didn't go further down that path.

https://docs.google.com/spreadsheets/d/1c3XQoc8EcwDdMsnPR-BS5--745BCabZZrsURfPMtvwI/edit?usp=sharing

This was the main issue, somehow it's always the fancy formulas that are right but the simple addition gets messed up. I should have caught that head volume and combustion volume were equal in column B sooner. When I fix that, I get a stock head volume of 49.5cc and the raised piston volume stays the same at ~16cc, as you've reached manually by iteration. Other values of the sheet remain unaffected, as that stock head volume is just for sanity checking once the raised piston volume is calculated . I added a tab to my sheet with the original head volume formula corrected.

The issue is that my head chambers are ~39cc, as I've measured directly. That is now a removal of 11cc from the calculated factory value, which is closer to the 4.54cc estimated value you proposed earlier (in the incorrect sheet, it was 17cc off). When I make a copy of your sheet and adjust the head volume to be what I've measured, we have the same values.
Another possibility to explain that misalignment is that the published stock head thickness may be incorrect? Or at least for my head? That would tidy all of this up nicely if that were the case.
Let me know if I've misinterpreted something there, but the 38.5cc is a fixed value. The sanity checking is much appreciated!


Sidenote as it didn't create any issues here: the difference in formulas for combustion volume between B and C was a remnant of working backwards a different way, but it happened to not matter as the subtracted value was 0. That's just the inverted static compression ratio.

Further sidenote: I'm basically ignoring dynamic CR here, as I intend to keep the stock camshaft. Matching static CR should keep everything in order for this particular rebuild.

If anybody has a stock 697-04 head laying around and could cc it that would be great! I'd be willing to send you the supplies for it. Might make a separate thread for that for visibility.

[GavinT]

Alrighty, let's accept the 38.50cc chamber volume because it's an empirical measurement.
Without argument to the contrary, we also need to provisionally consider "Head Volume (cc)" of 49.50cc because it results in the published compression ratio.
Obviously those two numbers are at odds.

There's 11.00cc missing.
If we accept the head skim accounts for ~3.50cc, we still need to find ~7.50cc thus:
38.50 + 3.50 = 42.00cc

Initially, I couldn't convince myself the space above the piston would account for 7.50cc because the raised plateau of the Lotus pistons is quite broad.
For that to make sense, the top of the piston plateau would need to be ~2.00mm below the liner height, but perhaps that is the case.

Need more data.
I reckon the next step is to discover the total volume via JB's method.
Alternatively, use the Lotus piston/liner kit from R-16Shop and get a 2.7mm custom head gasket. In saying that, I'm not sure how the rubber perimeter seal around the camshaft might handle a thicker gasket.

Lots of basic caveats to be aware of around all this, too.
If the head has been skimmed, I'd assume it was overheated at some point. Given it also has low compression pistons, I'd wonder why. Was that part of the overheating issue or something else entirely? What if they also took a lick off the block and decked the liners to suit?
As I say, lots of caveats with an unknown engine - measure everything.

[314159td]

More measurements on the way! As I don't care about liner seals I'm going to rotate the engine (by rolling the car, not turning the cam pulley) and verify/measure that the pistons reach the top of the liner. That's one of the larger assumptions I haven't seen confirmed yet. Most engines do that...not all.

The low compression pistons are still puzzling; it means someone tore into this engine pretty early in its life, or it left the factory like that for some reason. The person that had the head skimmed said it was only about 4-5 thou removed, so maybe another person before that removed the bulk of the material? Perhaps they could only get low compression pistons and chose to raise the CR via a head skim?

I'm pretty set on just getting the Lotus pistons and liners, and machining some off the top to keep CRs in line. I hate sending stuff to the machine shop but that's an easy job on the lathe at work. Cheaper and easier than figuring out a custom gasket.

[Richard48Y]

I would be looking for a standard head.
Skimmed that heavily brings the entire valve train into question as well.
I think I have a "scrap" head here, that might actually be repairable with some welding.
Had a blown gasket between two cylinders and got notched.
I will look and see if it is still around.
Yours for shipping cost if I find it and you want it.

[314159td]

Eh, ~1mm is usually well within the limits on OHV engines and it seems like the adjusters have it in them. The pushrod geometry is a bit more aggressive with the cam this high in the block but I'll sketch up the geometry at a later point and determine if the rocker pedestals need to be shimmed and/or shorter pushrods made. That're really not much of a skim, compared to the 3-4mm on contemporary race engines that definitely do need need them.
Head is already built up with ground seats and valves, and passes the compressed air leak check, so it's going to make its way onto an engine eventually.

[jbcollier]

The minimum head thickness is not to do with CR but with position of the cam lobe on the follower.  It will still run, no problem, but cam/follower wear will be higher.  This is not a factor in frequently overhauled racing engines and I have seen a couple of successful race engines with aggressively shaved heads.  However, shortened cam/follower life may not be what you want in a street engine.

Renault engines are very strong but they do not like to be overheated.  Combine that with the fact the cooling system requires careful bleeding, it was not unusual for a careless owner to toast a head gasket or even engine.  This is why most Europa projects are discovered headless and/or with replacement engines.

Please, please do not machine your new pistons until you get a correct CR calculation.  It is possible to weld and machine piston crowns but it ain’t cheap!

[Bullnose]

As an old (85) engine engineer, I am very much enjoying this discussion.

I am amusing myself by working through a cross flow engine that had some debris go through it.
You will find it interesting to pull the liners out - mine had at least a 1/4" of rust all over the water side. The inside was glazed with small scratches but cleaned up with a hone and is within usable tolerances.
I won't get into the details but can add comments re potential parts suppliers.
I placed an order with the Renault shop about 2 weeks ago. They accepted the order and asked me to wait until they send an invoice before paying. I am still waiting, despite a follow up email.
Another potential good parts supplier is der franzose (www.franzose.de) in Germany.
I placed an order with them on a Sunday night several weeks ago, called them the next day with a question about the order and it had already been dispatched. That's the good news! They ship with DHL and it was sent by sea. No projected delivery date is yet available from the DHL site.
Their prices are slightly better than the Renault Shop based on my shopping list.
I would be interested to know where you located the special head tools.
Thanks and keep up the good work.
Grant

[314159td]

Engine is out after building a gantry frame from definitely not untreated 4x4s, surprisingly easy with the harbor freight load leveler. I might make a post about this setup as it does pretty well in place of the proper lift sling tool. Was very surprised that the engine (w/o head) and transaxle balance like this.

[314159td]

I think I found the weird engine discrepancy!

The place I was pulling data from, Dave's page here uses a 697-02 engine to compare to the Lotus tuned 697-04, not the -01 found in the standard R16L. The -02 must be the low compression version of the engine for certain export markets, as it has a 7.6:1 compression ratio rather than the 8.6:1.

Anyway, changing that on the sheet, I get a 3.66 cc delta due to the head skim, right on what Gavin was getting at. Leaving the pistons at their full crown would give 11.1:1 CR, which is very reasonable but I think it'll take them down a hair for our piddly 91 AKI.

Thanks all for poking around!
The DMV has attempted to charge me $960 in back fees on the parallel project, so the Europa is back in focus while I wait two months (or more!) for them to read their own handbook.