Reassembling my crossflow

[GavinT]

I like your method, JB - simple, elegant and foolproof.

[califkid_66]

Both ways to measure are pretty good  but it would seem easier to do it your way JB  one thing i don’t understand is  ok to smear to seal piston then install and torque head  fill spark plug hole with light oil then you’ll know size of combustion chamber but after do you disassembled the head and clean that up or once your head is installed it stays there and just crank a few times to empty combustion chamber sorry im really easy to  confuse
Thanks

[jbcollier]

I suppose you could leave it assembled but usually you would remove the head after checking the combustion chamber volume.  Once you have your compression ratio calculated, you would make any adjustments required and match chambers, etc.

[GavinT]

G’day califkid,

Correct me if I’m wrong, but in your case you are just needing to establish the compression ratio to be sure it’s suitable for a road car, yeah?

If so, and given you already have the head off, I’d just use JB’s brilliantly simple method.
Just one caveat; be sure to install the old head gasket and also smear that with Vasoline on both sides to ensure a seal.

For the clean up afterwards you probably won’t be able to get all of the Vasoline that went down between the piston and the bores but that’ll disappear in the first puff of smoke when it’s fired up.

[califkid_66]

Yes  Gavin   i just wanted to know what the compression ratio was to give me an idea of what i have it should be 9.25:1 but the head as had some work done so there are a lot of variables witch will affect the compression ratio so i will measure it to know exactly
 

[califkid_66]

Today i did some measurements i used my caliper and a 10 cc syringe
I measured everything 3 times
and used the program from summit

Bore    79 mm
Stroke 84 mm
Cyl head volume 32.373
Dome volume 1.5
Deck clearance 0   Used a straight rule piston flush with liners
Compressed gasket .050

I measured the thickness of the head 3.625 in

According to my measurements my compression ratio
Is 11.26:1

Was thinking i was gonna be around 9.25:1
I don’t get it maybe my head as been shave to get more compression
I don’t have my books yet to compare numbers

[GavinT]

Hmmm . .

Is that 0.50 field entry meant to be .050” ?
For me, the Summit calculator didn’t seem to like mixing imperial and metric measurements and using .050”, it calculated a silly 5.42 : 1.
I changed it to 1.25mm which is close enough to 0.50".

Also, the Effective Dome Volume is supposed to be -1.5, not +1.5 because the dome reduces the combustion chamber volume.
After those changes it calculates to a Compression Ratio :12.08 : 1.

[GavinT]

Here’s another calculator.
http://www.csgnetwork.com/compcalc.html

I guessed the gasket bore diameter to be 80mm.
Calculated result was: 11.71 : 1

So, there’s some differences between the calculators.

With that large raised area on the pistons, I was doubtful it’d still be 9.25:1. Wasn’t that the stock CR with flat top pistons?

Anyway, there’s ways to get it down a bit. It’d be worth examining the pistons to see if some of that flat plateau could be taken off without compromising the crown. Maybe machine a (more or less) symmetrical dome like the 17TS pistons?
I’d nearly bet there’s some excess material on the left hand side of the plateau in your pics that could be deleted. An engine guy should be able to advise & guide.

A thicker head gasket would get you closer, too . . or a combination of these things.
Do you have a pic of the combustion chamber?

Did you do this using JB’s method?
It kinda looks like you might have done it “freehand” without using  a plexiglass plate.
Using JB’s method, you’ll get all the variables accounted for in one fell swoop.

[califkid_66]

The pistons are not crowne they are flat  no protrusion i put a straight edge  on them at tdc they are the same height as the liners on three sides they are a bit lower by 1.5 cc i filled the cavities with oil to make the piston flat so the 1.5 cc as to be added to the combustion chamber
I put the deck at zero cause the piston was the same height as the liners
For the cylinder head volume i filled up with the syringe until it was flush and it gave me the same result  3 times 32.373 cc
I measured the gasket  .050 inch witch is 127 mm same results
Bore is 79 mm stroke 84 mm measured with my caliper
so all my measurements where entered in the program and the results 11.26:1
All the measurements are correct
I will try to calculate manually

If my compression ratio is to high i can remove some material from the combustion chamber  what is circle in red

[califkid_66]

The last calculator didn’t ask how many cylinders
I found another one used mm and cc
It gave me the same as summit

[GavinT]

G’day califkid,

Curiouser and curiouser . . . but we ain’t stumped yet.
So, two things:

1. I can’t recall exactly, but I’m nearly positive the combustion chamber volume on a stock head is over 40cc’s.

2. What is the thickness of the head?
The stock 807 engine is 3.681” (93.50mm) and I’d expect the 843 to be the same.
To this end, could you provide a pic showing that small narrow channel at the hole where the dizzy mounts?

Your combustion chamber has already had some material removed (red circle).
You can remove more but it apparently starts to get close to the water jacket, so be careful if you go this route. Also, there’s no real way to know how close you are and there’s the additional possibility of accidentally creating localised thermal issues.

That said . .

[califkid_66]

Hi  Gavin  my head is 3.625 inch
as for measuring the combustion chamber i was doing it wrong
I remeasured using a plexiglass with a small hole on the chamber and i filled it up with water until all the air was out
the results where much different  i have 36.5 cc so i redid the calculator and it gave me
9.16:1  compression Ratio wich is perfect

[califkid_66]

Is this the part you wanted to see let me know
And by the way i was told it was a real gordini head and the intake valves are 42 mm and exhaust valves 35 mm  i have 36.5 in combustion chamber on head and im gonna remeasure my dish on piston witch was giving me 1.5
So if you add them up im at 39 total my 1.5 might be off but like i said im gonna check again

Also you wrote stock head  is 3.681 mine is 3.625 that’s  0.056 difference witch could account for the
différence in size of the combustion chamber

[GavinT]

Hi califkid,

Result! . . that’s good news then.
Actually, at 9.16 compression you’ll probably be looking for a thin head gasket to get it up a bit.

Thanks for the pics.
Yes, I wanted to see the small cast in channel. It’s a very crude measure but it does provide a quick visual guide as to whether the head has been skimmed because it disappears quickly if it has.
In your pics and my last one, it’s gone completely. No biggie.

Just so you know, I wouldn’t get too attached to the “real” Gordini head thing.
Amedeo Gordini was a Renault tuner (among others) and made a name for himself at Renault with the Dauphine in the late 50’s.

The Renault 12 Gordini, and the similar engines found in Alpine 110’s were a much later development and it’s highly unlikely Amedeo had a hand in those. All that later stuff morphed into Renault Sport somewhere along the line, but Renault still use the Gordini name as a marketing distinction . . and, hey, why not.

That said, it’s good yours has the larger valves. That's a plus.
This is the one I could really lust after.

[califkid_66]

Ya that’s good news! I know how to measure now i was to much in a hurry and skipped some steps and im not use to this type of measuring but i now how to use plastigage micrometers and calipers  so im gonna check all the moving parts
I don’t need the engine right now so im gonna Read the books i ordered and follow the steps to put it back together 
I still have my wedge in the Europa im in no rush to finish the crossflow but the plan is to put it in for next summer
Thanks for your help