1959 4cv Restoration in North Carolina USA

Increasing the volume would lower the compression ratio. I don't know what is considered too much for these engines. I found a compression ratio calculator.

Compression Ratio (CR) Calculator - Good Calculators

This compression ratio calculator can be used to work out the compression ratio of your engine. The compression ratio is the ratio between two elements: the gas volume in the cylinder with the piston at its highest point (top dead center of the stroke, TDC), and the gas volume with the piston at...
goodcalculators.com goodcalculators.com

The head gasket measures 1.35mm, so if I assume a thickness of 1mm when tightened, this calculator gives me a value closer to 8.1 to 1. I certainly don't want the ratio less than that.
 
The only reason to lower compression would be if it were too high to work on normal fuels. I am planning on running regular 87 octane fuel.

The replacement pistons have an arrow on the top at 90 degrees to the gudgeon pin. Which way should the arrow face? All my manuals describe pistons with marks in the same orientation as the gudgeon pin.
Img_2671 - Copy.jpg
 
I think the gudgeon pin is offset. The pistons would be installed one direction for the 4cv and Dauphine, but the other direction for the R4 (engine turns in opposite direction). My best guess is that the arrow indicates direction of rotation, but I don't want to guess.
 
I have seen some instructions with pistons that say the arrow should point to the cam shaft. Not saying that that is your situation though.
 
Love that old water distribution tube! I'm no authority on compression ratio but with modern fuels...... I'd leave well alone I think.
 
Stan W said:
The only reason to lower compression would be if it were too high to work on normal fuels. I am planning on running regular 87 octane fuel.

You will be fine with 8- 8.5 to 1 comp ratio. I know of a Dauphine engine over here running 10 to 1 on 98RON which I believe is like your 93MON fuel. It has a pair of carbs, and some porting, but the standard Dauphine cam. It goes quite well.
Click to expand...
 
*My Dauphine is on about 8.7 : 1 compression. I usually use 98 or 95 RON, but occasionally use 91 RON without any noticeable ill effects.
*The arrows on my 60mm pistons were supposed to point to the camshaft side, but different pistons may have different marking conventions.
*One reason to increase combustion chamber volume would be to widen the combustion chamber to reduce valve shrouding. You've increased the bore by 3.5mm and there was probably some scope for widening/de-shrouding with the original liners. If you precisely locate a 58mm head gasket on the head and run around the combustion chamber cut-out in the gasket with a felt pen, this will show you how much you can relieve the head in this area. Also, you might consider doing a little radiusing of the liner tops in this area with the same objective. In spite of what some Aussiefrogs correspondents have said, I've always found de-shrouding of the valves to be very productive. The ratio that we calculate by dividing BDC volume by the TDC volume is a theoretical ratio only. The ratio that counts is a dynamic ratio of pressures. Losing a couple of points of the theoretical ratio doesn't matter if flow is increased by a greater amount.
 
Last edited:
Stan W said:
The only reason to lower compression would be if it were too high to work on normal fuels. I am planning on running regular 87 octane fuel.

The replacement pistons have an arrow on the top at 90 degrees to the gudgeon pin. Which way should the arrow face? All my manuals describe pistons with marks in the same orientation as the gudgeon pin.
Click to expand...

I suspected you would say something like that but like Alan I don't think you should have any problems with lower octane fuel.

Now, 87 is quite low. I don't think I've ever used that in any of my cars. Full disclosure, I have driven many R12s, R8s and R10 (pretty similar engines) and they were very picky. All of them. They didn't like anything other than 98. No detonation/pinking but with 95RON they would feel like the fuel was dirty. These were Euro engines. In Oz, I have only driven a few R12s and they didn't like anything other than 98 either but I have never driven an R10 or similar here.

As for arrows, as you've heard above, they can point at any number of things. Across the gudgeon pin (some have arrows along the pin as you say) they probably point to the thrust face which is I think (from faded memory, so check) the camshaft side on the 810 family of engines (R12 and similar). If the arrow points in the direction of rotation as you suspect, the thrust face would be the opposite side.

Ultimate answer should be the piston manufacturer datasheet.

If no joy, measure if the pin is indeed offset and the thrust face is the one with the offset (smaller distance bore to skirt). That face is opposite the pointy end of the arrow when you have the arrow point at the rotation direction. In other words, the offset side helps determine the direction of rotation hence which way the piston is installed. That will clarify what is pointed at by the arrow.

See this:

http://www.chevydiy.com/wp-content/uploads/2015/03/6.jpg
 
Last edited:
The octane rating in the US must be different from Australia. We don't have 95 or 98 at normal petrol stations.

I found the exact same picture of gudgeon pin offset. The pin is offset 1mm, one of my books mentioned that. The smaller distance (bore to skirt) is opposite the pointy end of the arrow, so the arrow does point in the direction of rotation.
To muddle things a bit, I checked the pistons that had last been in the engine (it was disassembled when I bought it). They were Dauphine size pistons and the arrow that clearly points toward the front puts the offset in the wrong direction! They were probably an aftermarket piston, so who knows....maybe they were labelled for the r4 ventoux engine which turns the other direction. Here is a picture of the cleaned up old piston.
IMG_2672 - Copy.JPG
 
Stan W said:
The octane rating in the US must be different from Australia. We don't have 95 or 98 at normal petrol stations.

I found the exact same picture of gudgeon pin offset. The pin is offset 1mm, one of my books mentioned that. The smaller distance (bore to skirt) is opposite the pointy end of the arrow, so the arrow does point in the direction of rotation.
To muddle things a bit, I checked the pistons that had last been in the engine (it was disassembled when I bought it). They were Dauphine size pistons and the arrow that clearly points toward the front puts the offset in the wrong direction! They were probably an aftermarket piston, so who knows....maybe they were labelled for the r4 ventoux engine which turns the other direction. Here is a picture of the cleaned up old piston.
View attachment 131173
Click to expand...
Maybe they were assembled wrongly too.....
 
Stan W said:
The octane rating in the US must be different from Australia. We don't have 95 or 98 at normal petrol stations.

I found the exact same picture of gudgeon pin offset. The pin is offset 1mm, one of my books mentioned that. The smaller distance (bore to skirt) is opposite the pointy end of the arrow, so the arrow does point in the direction of rotation.
To muddle things a bit, I checked the pistons that had last been in the engine (it was disassembled when I bought it). They were Dauphine size pistons and the arrow that clearly points toward the front puts the offset in the wrong direction! They were probably an aftermarket piston, so who knows....maybe they were labelled for the r4 ventoux engine which turns the other direction. Here is a picture of the cleaned up old piston.
View attachment 131173
Click to expand...
The octane ratings are different in the US and Canada I was struggling as well trying to sort out a compression rating it turns out that our 93 octane comes in around 95 or 96 rating in Europe so probably the same in Australia ! A 10 : 1 compression rating would be fine on our 93 octane !

Enjoying reading about your build !

Manic GT
 
Hehehehe! How can octane ratings be different?! Well, it seems somebody found a way. I think it's because your pistons are made of Aluminum.

No matter. I would install the pistons by the way the gudgeon pin has to go regardless of markings and stuff. Again, manufacturer datasheet is invaluable here.

Abut the front of the engine, that is again confusing given Renault has used the same engine this way and that way in various cars. Sometimes book refer to the flywheel, which is a bit more reliable, and I am sure I have seen pistons with markings pointing at the flywheel.
 
schlitzaugen said:
Hehehehe! How can octane ratings be different?! Well, it seems somebody found a way. I think it's because your pistons are made of Aluminum.

No matter. I would install the pistons by the way the gudgeon pin has to go regardless of markings and stuff. Again, manufacturer datasheet is invaluable here.

Abut the front of the engine, that is again confusing given Renault has used the same engine this way and that way in various cars. Sometimes book refer to the flywheel, which is a bit more reliable, and I am sure I have seen pistons with markings pointing at the flywheel.
Click to expand...
US octane rating vs Europe
In Europe, the octane rating on the pump is simply the RON figure. America, by contrast, uses the average of the RON and the MON figures, called the AKI (anti-knock index). Thus, 97 octane “super unleaded” in Britain is roughly equivalent to 91 octane premium in the United States.

This helped me understand why and how much compression I could build in my projects !
Manic gt.
 
Thanks for clearing up the octane issue. The flywheel end is usually the front for the ventoux engine - but the R4 ventoux turns in the opposite direction from the 4cv. I found that others also had questions about the orientation of the Aprotec pistons. The answer is first check the offset, but generally, the arrow points towards the direction of rotation. There is nothing on the Aprotec site that sheds any light on the subject. To sum up, the gudgeon pin is offset to the left (standing at the rear of the car) since the engine rotates clockwise.

Attached is a picture of the outline of the head gasket showing areas that could be modified to reduce valve shrouding.

Img_2673 - Copy.jpg
 
Stan W said:
Thanks for clearing up the octane issue. The flywheel end is usually the front for the ventoux engine - but the R4 ventoux turns in the opposite direction from the 4cv. I found that others also had questions about the orientation of the Aprotec pistons. The answer is first check the offset, but generally, the arrow points towards the direction of rotation. There is nothing on the Aprotec site that sheds any light on the subject. To sum up, the gudgeon pin is offset to the left (standing at the rear of the car) since the engine rotates clockwise.

Attached is a picture of the outline of the head gasket showing areas that could be modified to reduce valve shrouding.

View attachment 131208
Click to expand...
How much can be removed before your compression numbers go down to much ? What is cc of head at this point and how much can be shaved before trouble starts ?
 
manicgt said:
How much can be removed before your compression numbers go down to much ? What is cc of head at this point and how much can be shaved before trouble starts ?
Click to expand...
The head has already been shaved about .030", so that is about all that is recommended, and more than the manual states. The cc of the combustion chamber is now between 24.5 and 25cc. The compression ratio should currently be between 8.2 and 8.9. I am thinking of leaving it as is. I am already past the limit of previous experience in this respect. The engine should have at least 25% more power than the original 28 hp.
 
Stan W said:
The head has already been shaved about .030", so that is about all that is recommended, and more than the manual states. The cc of the combustion chamber is now between 24.5 and 25cc. The compression ratio should currently be between 8.2 and 8.9. I am thinking of leaving it as is. I am already past the limit of previous experience in this respect. The engine should have at least 25% more power than the original 28 hp.
Click to expand...
On any of my North American projects I like to aim at about 9.25 to 9.5 to one compression ratio it allows me to run 89 North American octane ! the aluminum head should convey the heat away nicely so should be plenty safe !
 
Stan W said:
Thanks for clearing up the octane issue. The flywheel end is usually the front for the ventoux engine - but the R4 ventoux turns in the opposite direction from the 4cv. I found that others also had questions about the orientation of the Aprotec pistons. The answer is first check the offset, but generally, the arrow points towards the direction of rotation. There is nothing on the Aprotec site that sheds any light on the subject. To sum up, the gudgeon pin is offset to the left (standing at the rear of the car) since the engine rotates clockwise.

Attached is a picture of the outline of the head gasket showing areas that could be modified to reduce valve shrouding.

View attachment 131208
Click to expand...
Are you sure that you used as 58mm head gasket? On the basis of that photo, all you can do is to 'break the sharp edges'. There's no significant margin for de-shrouding.
 
schlitzaugen said:
Hehehehe! How can octane ratings be different?! Well, it seems somebody found a way. I think it's because your pistons are made of Aluminum.
No matter. I would install the pistons by the way the gudgeon pin has to go regardless of markings and stuff. Again, manufacturer datasheet is invaluable here.
Abut the front of the engine, that is again confusing given Renault has used the same engine this way and that way in various cars. Sometimes book refer to the flywheel, which is a bit more reliable, and I am sure I have seen pistons with markings pointing at the flywheel.
Click to expand...
Hi :)
Interesting discussions you get into Stan. Renault and Citroen always(since the war ?) have used the flywheel end as the front of the engine even later when the engines were turned around or put sideways. So you count from the flywheel also for number 1. :cool:
Renault(and others) never recommends you take any metal off the head except for a skim. But back in the day people removed heaps more and never had problems. Common sense rules of course. I remember asking for a good cut done, not sure what I got, but it was OK on my first car. Those heads had plenty of "meat" in the castings and that will help with the extra power and compression heat.

It would be silly IMHO to reduce the compression as the knock rating of the fuel is so much better that the old days, however you measure it. Just break the sharp edges as Harris said. You can always easily adjust the timing to see how it sounds and goes. Not much sound proofing to hide the pinging :oops:
Jaahn
 
You must log in or register to reply here.
Top