Valve Adjustment Clearances

[redmt]

I was working on a buddies 3cyl diesel powered tractor and after setting the valves, I started to wonder how or what determines the valve clearance?
I have fiddled around with different settings before on Cummins NT motors to run the timing up and down a bit but how are the original clearances determined? How would you determine clearances for an unknown performance cam shaft?

John

[blykins]

The lash is determined by the cam grinder, which is based on the particular lobe design.

You can go either direction a certain amount to "fine tune" the engine. Closing the lash changes the effective duration of the cam, "fooling" it into thinking it's larger than what it is. Of course opening the lash up does the opposite.

If you had no clue on the cam or cam specs, I would start by getting a general feel of whether the cam is a roller or flat tappet, aggressive or lazy, etc. It should give you a ballpark.

[vector1]

i would guess you are talking solid tappet, you can put a micrometer on the pushrod or lobe or rocker and watch the needle from base circle to where it starts to climb the lobe at an accelerated rate. there will be a gradual increase at first, at the middle of this or closer to the base circle is where i would set the lash at zero on a hot engine, cold could be something else but probably close. probably not real critical on a low rpm mild camshaft, and listen for any odd "noises". or on a warm engine i might set it at something like .010 and let it go, works on b&s lawnmower engines.

[redmt]

Book specs couldn't be found for the little diesel. I used a rule of thumb/guestimate and went with a 12 and 15 setting. Runs just fine and I know it would run probably 3-5 either way. I'm wondering how the lash is determined except by the grinder pulling a number out of his ear? For the sake of this , lets stick to a flat tappet, mild say 270 to 280 duration cam. maybe spread the overlap a bit 110-112 and keep the lift around 5-550.

[redmt]

Originally Posted by blykins

The lash is determined by the cam grinder, which is based on the particular lobe design.

You can go either direction a certain amount to "fine tune" the engine. Closing the lash changes the effective duration of the cam, "fooling" it into thinking it's larger than what it is. Of course opening the lash up does the opposite.

If you had no clue on the cam or cam specs, I would start by getting a general feel of whether the cam is a roller or flat tappet, aggressive or lazy, etc. It should give you a ballpark.

What should give you a ballpark?

[Barry_R]

Between .010 and .020 at the lobe/lifter end will usually get you reasonably close on a mystery cam.

The variables/limits are noise/impact damage at the large end and "no start" at the low end of the common ranges. A cam designer will also take lifter diameter, lobe profile grinding capability and durability needs into account when making the choice.

[blykins]

On a lot of the Comp Cams stuff that I use, you'll see flat tappet cams with lash specs between .020-.026". On the roller stuff, you'll see .016-.018" on a lot of lobes. Then of course you have a little creative license either way on that.

Lash grows when hot, so if you open valve lash way beyond the lash ramp design, you take a chance of bypassing that ramp, which would allow a lot of "hammering" to go on with your valvetrain, instead of having a "gentle" open and close.

Conversely, setting it too tight can cause issues with hanging the valves open when cold.

[Jerry Clayton]

Barry and Brent---

Pretty much agree with what you have said but this guy has a diesel--

Lash does not necessarily grow when hot----depends on the total package of the engine--
an engine with alum block or heads does expand more than cast irom and needs to have a tighter setting than an cast iron block/heads--combo of iron/alum block/heads can vary to a degree also--

The differance of lash settings for the valves other than that comes down to the size/material/construction of the valves--the intake runs cooler than the exhaust---are the stems sodium filled to transfer heat from the valve heads to stems? etc, etc

On this guys diesel(if he would state what it is ) we could find the numbers he needs--however you can't just throw a number at it because the diesel (altho a lower rpm) runs at a much more critical set of numbers (similar to a race engine) and can't be assumed to just be a low performance daily driver type engine

[blykins]

Very true.

Valve lash on an iron block/iron head combo may not grow at all....or it could grow a few thou.

The original poster made a comment (4th post down) about how he would find out what the lash spec would be for a particular solid flat tappet cam....he gave the parameters as an example.

I agree, the diesel may be a totally different beast....and I don't have any diesel experience whatsoever, except for putting a new injector pump and timing belt on my dad's 1992 VW Jetta.

[redmt]

Everybody is going different directions! The original q was as to how specs were determined. In particular, the engine I happened to be working on at the time is in an old Ford 545A with a later model 3cyl diesel with no id tags. I'm sure if you were familiar with this machine series motor, you could ID it in a heartbeat. I pulled some numbers out of the air at 12 and 15 knowing that diesels traditionally use larger clearances on the exhaust. I gotta go fix another one, look forward to seeing some info later this afternoon.

J

[Jerry Clayton]

John

In addition to the materials the block/head(ford 545a is iron) the biggie is exhaust valve growth----

The cam lobe diameter will have some degrees of area that are designed to take up the movement gently and set it down gently instaed of slamming and dropping---

That differance is then modified by the rocker arm ration to end up with checking lash=

If working on a totally unknown deal--set the lash at .020 cold(won't be too far off either direction) start the engine and bring up to good operating temp--recheck clearance to see how much it moved---if it didn't move too much to indicate trouble--you can probably move the clearance down to area of .014 to .016

[Mr Jody]

John – I have a Ford Tractor operator’s manual that is identified as being for models 231, 335, 420, 515, 531, 532, and 535. I believe the 545 has an engine very similar to the 535. This manual may have preceded the 545, but since it identifies only this one setting for the whole series of tractors that it covers, then I would like to think that it would be a good number for the 545, unless the later model engine that you are working with is significantly different.
It specifies the settings as:

Intake……………….0.014 in. go ---- 0.016 in. no go
Exhaust…………….0.017 in. go ---- 0.019 in. no go

It does not specify if this is cold or hot, but I believe this is for cold, as I checked two manuals I have for some three cylinder Massey-Ferguson tractors (135; and 255, 265, 275 series) with somewhat similar size engines to the Ford, and the clearances for these are:

Hot - Intake and Exhaust….. 0.010” hot for both tractors
Cold – Intake and Exhaust…… 0.012” and 0.015” for the 135 and 255 series respectively

The above numbers for the Ford are more in line with the cold settings here, and I think the Ford manual would specify if they were to be set when hot. Hope this helps ease your mind with the settings you made. - Jody