Adjusting valve clearences?

[djones]

Hi guys,

When you adjust the valve clearences on a car and the specification says something like 0.16mm to 0.20mm would you rather be at the high end or low end of the scale?

[manchild]

For the sake of reliability (especially in case of overheating) I'd choose high end (greater clearance).

[djones]

Thanks.

I will aim for 0.19 then.

[Carlos]

When adjusting to wider adjustment tolerances I would suggest using a synthetic oil with good viscosity stability to help prevemt wear - an oil cooler is always a good idea - and inexpensive - I always installed an engine oil cooler plus a transmission oil cooler (when possible) on all the cars I owned.

[djones]

I always use a good Syntheic (Silkolene PRO S) and change every 5,000 miles.

Also, the car has an oil cooler as standard.

[mx_tifoso]

I always use a good Syntheic (Silkolene PRO S) and change every 5,000 miles.

Also, the car has an oil cooler as standard.

Would you mind giving us some insight (make,model, etc) on the car you are working on?

[Ciro Pabón]

If you're aiming for safety, Manchild is right. If you're aiming for tuning, take in account that a looser setting increases power of the engine at low RPMs, while a tighter one increases top-end power.

In an ideal world a valve would open or close instantly. This way you'll maximize the flow of air or exhaust gas for any given opening time.

In practice this is impossible. Race cams get as closer to this ideal as possible usign heavier valve springs to close the valves faster and follow the cam. One thing we can do to help power with a stock cam is to INCREASE the valves running clearance slightly, taking in account you will not reach high RPM normally.

Camshafts are designed to run as quietly as possible in your road car, and have what is called "quietening ramps" on both the opening point and closing point of the camshaft. Now, for several degrees of engine rotation the valve is lifting (or returning) slowly. This means that its not sealing, thus shortening power stroke. Setting the valve clearances to the larger end of the allowable range gives more power, while maybe giving you some valve noise.

I would love to hear some comments on that one. I've discussed about it with a friend for ages. The amount of power is not negligible: many, many years ago we tried to measure it with a dyno and we were confused in the beginning because we measured only max power at max RPM, obtaining the opposing result of what we expected. The change in power was around 10 HP in a 200 HP engine.

[Carlos]

Camshaft ramp profiles - an exotic subject - worth years of discussion - using a 'fast' ramp can dictate the use of heavier valve springs to control valve float - and heavier valve springs can result in loosing power.

[djones]

Sorry, I should have said. It's a 1999 Honda Integra Type R.

I use it for hard weekend use mainly as I have an old Civic for work. It revs to 9000 so as far as road engines go it's highly strung.

It uses titanium valves and things I think to keep the masses down at high revs. I will double check that but im sure I read it somewhere.

[img::]http://us1.webpublications.com.au/stati ... 04_1mg.jpg[/img]

Here is a graph from a rolling road session I had a few weeks back...



I spend a fair bit of time up over 6000 RPM as thats where all the main power is.

The actual specs Honda specify are:

Inlet 0.17-0.19mm
Exhaust 0.19-0.21mm

A few people say to do them when hot but Honda specify COLD so i'm not sure where they get that idea from???

[Carlos]

Here is a worksheet that may be helpful:

http://www.smccd.edu/accounts/mcafee/La ... sheet.html

[DaveKillens]

Nice ride, djones, sweet ride.
First off, always follow the manufacturer's instructions unless you have a very valid reason for straying off the path.
The reason for this specific setting is to make sure that when hot, the valves seat fully when they are supposed to. It would be a disaster to have a situation where when hot, any valve does not seat fully when closed. It would burn the valve up, and that is definitely not good.

[Ciro Pabón]

I hardly can believe you drive your car at 6000 rpm all the time. Don't you shift gears once in a while?

If you're in dragsters, the power you have to measure is when revs are slightly down from your maximum (think about how much power you use at 6000 rpm: your engine stays there for a few tenths of a second!). If you want to adjust your car for optimum power, look for the middle of the RPM range you use. For example, if your gear ratios take your engine from 4.000 to 6.000 rpm while you're racing, tune the engine for 5.000. If you're an artist (or a neurotic) of tuning, look for the RPM range you will use at the overtaking points in the track. Tuning for max RPM and max torque is only when you want to sell the car in Road & Track magazine or you're planning to break a speed record at Bonneville Flats.

I've never heard of adjusting valves when hot. That's definitely a huge no-no, as Dave explains.

I've seen a method (that I don't recommend because I don't like to run a block with bolts removed, afraid of ANY thermal distortion) to check the clearance. You run the engine with the valve cover removed and you pull the gauge, to "feel" the clearance" (allegedly, you has to feel like you were stretching bubble gum).

Of course, you have located the gauge between the valve and the seat before starting the engine. This has to be done with the engine as cold as possible (running it for a few seconds and turning it off and allowing it to cool before checking the next valve). You have to test the clearance definitely under 100 degrees of engine temperature, as stated in most specifications I've seen that mention temperature explicitly.

Why, in heaven's name would you want a clearance at all when valves are hot? The clearance "is there" to adsorb the thermal expansion, for Benz's sake!

I think I know where they got that idea: from the always popular "Department of Ideas We Take Out Of Our *ss".

[djones]

Thanks for the techinical replies. It's all very interesting!

Ciro Pabón - If I'm just out for a blast over country lanes etc I will let the car warm up then will usually be between 5000 and 9000 not taking into account traffic etc. It's not slow under them revs but the noise and everything just make you stay right up there. At 6000 the Cam profiles change over, the noise gets a lot more aggresive and it picks up a bit. Then at about 7500 it really picks up and doesn't let off until the 9000 limit. It's quite impressive really for a reliable 1.8 made nearly 10 years ago.

In the original brochure about the car Honda said "...And it's relatively long stroke and high redline gives it the highest piston speed of any automobile engine in the world, even faster than the lefendary World Championship Formula One and IndyCar engine"

I'm guessing the F1 engines in 1998 revved higher than 9000, so I'm not fully sure what they mean by higher piston speed??

[Ciro Pabón]

Simple, djones: piston speed is a function of RPM and stroke. Your car has a longer stroke than an F1 engine, meaning it moves faster up and down (because it has to move a longer distance on every stroke), even if the crank rotates slower. For your car to have the same piston speed as an F1 at 18.000 rpm, your car being at 9.000 rpm, then the stroke of your car has to be double the length of the stroke of an F1. If the stroke is slightly over double of the stroke of an F1, you have higher piston speed at half the RPM.

[djones]

Ah, of course. I didn't look at it like that, thanks!