Measuring Cylinder Capacity

[Mike45]

Not sure if this is the correct place to post this question and I am sure it must have been asked before but I’m unable to find any references.

Problem. Scrutineering for a small championship. We need a method of determining cylinder capacity to within about 10% or better without head removal. Accurate measurement will be done later with head removal. There has been talk of a device or devices that can be connected via spark plug openings but is this just wishful thinking?

Any advice, links, tools, ideas or specs would be gratefully appreciated.

TIA

[mark_l]

Would it be possible to use a vacuum device and measure the air extracted from each cylinder?

[greenamex2]

You couldn't extract the air because a cylinder is not anything like perfectly sealed.

I believe there is a device in the states that fills up the cylinder with a 'balloon' to measure capacity, but I think it was restricted to OHV engines and can't find any details.

[GORDON STREETER]

It is possible with "some engines" if a way of keeping the valves closed on the cylinder being measured can be found.
Obviously with a pushrod engine you can remove the rocker shaft but not on an OHC.
You then put the piston at BDC and fill the cylinder with thin oil to the bottom of the plug thread.
Make an "attachment" out of an old spark plug base with a hose fitted to it going into a measuring flask .
Turn the engine to TDC remove the plug adapter pinching the pipe to make sure that you don't lose any oil out of the "complete attachment" and drain that into the measuring flask as well, that is the swept volume of that cylinder.
I believe you can buy laser measuring devises to do this but at a price and would need a trained operator.

[Al Weyman]

There is a device from the States that does this but its about $1000 it also as Gordon states, requires valves to be closed and a complete cycle of the engine, with a push rod engine this is simple, just let off the lash, with an OHC engine it would mean removing the camshafts, still better than an engine strip IMHO and I tried to get CTCRC to invest in one but there was no interest???

[Al Weyman]

Found one here they have gone up a bit! http://www.powerhouseproducts.com/ph...o-670-c-i.html

[GORDON STREETER]

Mmm that makes my homemade device for under a tenner sound a bargain !
I should have said that "some" OHC engines have rockers that can be removed easily

[Al Weyman]

it is the Holy Grail of club motorsport thats fpr sure.

[Mike45]

Thanks for all the thoughts and the link. I'll see what the championship would like to do.

[GORDON STREETER]

I don't think that there will be a device that will suit what you want as most modern vehicles are single or double OHC.
If you can scan the bore size with a laser device through the plug hole you can check the stroke with a rod down the bore,

[Al Weyman]

What laser device will do that Gordon?

[GORDON STREETER]

I don't know Al, I would assume that it must be possible in this day and age of cheap electrical gizmo's though ?
My heath robinson cheapo measuring device always gave me a pretty acurate reading and I made that about 40 years ago !

[Al Weyman]

It seems like there isnt but it would be great if there was, championships like CTCRC thats about the only engine reg apart from based on stock block etc that there is, if that was easy checked without a strip down it would prove or disprove a lot.

[dtype38]

I've not tried this, but I think it would work on engines where the spark plug is sufficiently in line with the bore to slide a rod all the way to bdc parallel to the bore.

Stroke: using a rod parallel to the bore, measure the height of the piston at tdc and bdc and taking the difference.

Bore: put the piston to bdc and fill the bore with sufficient light oil to ensure the crown of the piston is fully covered, say about a third of the way up the bore. Use the rod above as a dip stick to measure the height to the surface of the oil. Now add an exactly known quantity more of oil (pick an amount that will fill the bore to say two thirds full) then again measure the height of the surface of the oil. For a vertical bore the maths is then quite simple to use the two heights and the volume of oil added to find the bore.

For an inclined bore like on a V8 it would be a little more difficult, but still possible. Care would need to be taken over the amounts of oil so as to fully cover the piston with the first amount, then not touch the chamber with the second (jacking up the car on one side might be needed). The maths is also somewhat more complicated, but knowing the angle of incline, two measured heights and the volume of oil added it should still be possible to work out the bore reasonably accurately.

What do you think?

[fourWheelDrift]

Originally Posted by dtype38

I've not tried this, but I think it would work on engines where the spark plug is sufficiently in line with the bore to slide a rod all the way to bdc parallel to the bore.

Stroke: using a rod parallel to the bore, measure the height of the piston at tdc and bdc and taking the difference.

Bore: put the piston to bdc and fill the bore with sufficient light oil to ensure the crown of the piston is fully covered, say about a third of the way up the bore. Use the rod above as a dip stick to measure the height to the surface of the oil. Now add an exactly known quantity more of oil (pick an amount that will fill the bore to say two thirds full) then again measure the height of the surface of the oil. For a vertical bore the maths is then quite simple to use the two heights and the volume of oil added to find the bore.

For an inclined bore like on a V8 it would be a little more difficult, but still possible. Care would need to be taken over the amounts of oil so as to fully cover the piston with the first amount, then not touch the chamber with the second (jacking up the car on one side might be needed). The maths is also somewhat more complicated, but knowing the angle of incline, two measured heights and the volume of oil added it should still be possible to work out the bore reasonably accurately.

What do you think?

That's actually very clever though could be fiddly and time consuming to do accurately.

[dtype38]

Agree it would be tough to do on a short stroke engine with heavily domed pistons, but on the old under-square stuff I'm used to it could be quite accurate :-)

[wnut]

Clever! Good work dtype38.

[Al Weyman]

Removing the oil may.be fun.

[dtype38]

I'have done some measuring of actual chamber volume (ie volume of chamber including gasket etc with piston at tdc) using oil down the plug hole. I simply set the piston at tdc firing stroke and measure oil in until it reaches the top of the spark plug hole. Subtracting the volume of metal in plug gives a pretty accurate measurement of real chamber volume. Taking the oil out is then just a matter of lowering the piston a bit then using a big syringe with a thin bit of plastic tube on the end. Any residual oil burns off pretty quickly.

Going back to the method I suggested though, if its just swept volume that's needed to be measured (not actual bore) then the maths is a doddle:

Swept Vol = Control volume of oil added x (stroke / height change in oil level)

"height change in oil level" being the difference between the two dipped heights when the control volume of oil is added (with the previously mentioned provisions about piston crown and chamber edges).

Ie if the stroke is 8cm and adding 100cc of oil give a rise in height of 2cm, then the swept vol = 100 x (8/2) = 400cc

I believe I'm correct in saying that this works even if the cylinder is inclined (so long as "height" is measured parallel to the bore).

[GORDON STREETER]

The only problem with your idea dtype on combustion chamber CC is that with your method it doesn't allow for any air that could be trapped in the top of the combustion chamber, this is important especially on a small CC engine
My way of doing the engine size check is very accurate and shows instantly the swept volume in CC of the cylinder straight into a measuring flask and its simple, even a trained monkey (like me) can do it
I don't use oil by the way I use diesel.

[dtype38]

Completely agree Gordon, you method is more accurate and more easily measured. I was just trying to think of a way getting an answer within 10% (as the op was after) for engines on which its hard to "disconnect" the valves.

RE: air bubbles, my spark plug holes are pretty much at the top of my chambers. But I did say that was a method I used, not that it was generally applicable.

Oh, one other thing... sorry, sorry, that last statement about the maths being the same for inclined bores isn't true. I was thinking through the maths a bit more rigorously in the shower this morning and another multiplication factor is needed for a inclined bore. It's the minor to major chord ratio of the horizontal ellipse which exactly fits the bore. The number is independent of bore size, just on inclination angle, so could be tabulated for easy reference. Sorry again.

[GORDON STREETER]

Originally Posted by dtype38

Completely agree Gordon, you method is more accurate and more easily measured. I was just trying to think of a way getting an answer within 10% (as the op was after) for engines on which its hard to "disconnect" the valves.

What's the problem ? just cut through the cambelt with a stanley knife or use an angle grinder on a chain !

[JohnD]

Been turning this over in mind.
Oil? Messy!
Measurements? Doing them blind, or with long reach instruments v.diificult.

How about measuring the volume of air that is expelled on the compression stroke?

Spark plug adaptor, similar to a compression tester, with a tube to a large medical syringe. 100-150mls syringes available on eBay (don't ask what they are for)
The stroke volume will be several hundred mls, so several fills of the syringe will be needed as the piston rises. Before each change of syringe, the pressure in the system should be equalised with atmospheric by a water filled U-tube on a side arm, by adjusting the syringe piston.
If you can find a syringe with a capacity greater than your bore that would make it easier, but the bigger the syringe the less accurate the volume measurement.

The only possible mess would be the water U-tube, which could be replaced with a pressure gauge, or even a membrane that should be flat when equalised. All under direct vision, easily and quickly repeatable, so the mean of several measurements could betaken to reduce error.

John

[Al Weyman]

Wouldnt work with a large overlap cam though would it?

[GORDON STREETER]

Or a normal cam in any car, you have still got to keep the valves closed !