Valve Lash Procedure for 6CTA 8.3 430 HP

[Kevin]

Hi All,

Have googled and searched the forum, but can’t seem to find an answer for the procedure on valve lash adjustment. I have adjusted valve lash on many engines, so knowing where the timing pin is, plan to turn the engine over by hand until it engages. Confirm #1 is TDC (assuming most forward cylinder).

I could go one cylinder at a time following the firing order, but on other engines I have had I was able to adjust several cylinders at once as there valves would be closed as well.

Is there a procedure for the 6CTA that gives that info? I bought the ops and maintenance manual from SBMAR and it refers me to another manual.

Thx in advance!

Topic

[Kevin]

4 Stroke description

@tony and @bluebyu thank you for the info!

I started on a FORD 390 FE on my dad’s 1974 f-250 and progressed to rebuilding my first diesel which was an international 7.3 IDI (pre-Powerstroke) with a Standyne Rotary injection pump. I worked on my first HEUI engine shortly after which was an International DT466E. The largest diesel I have worked on was a CAT 3512, it was so big it was a piece of cake to work on because everything was just big and spaced out.

To elaborate for folks who aren’t fully versed in the 4 stroke engine, the reason you can adjust the exhaust valve prior to TDC is that on the compression stroke the exhaust valve will be closed, but you have to make sure you are on compression and not exhaust stroke (this should be obvious when looking at the rockers, or an overhead cam motor the cam lobes as the rockers will be the same or the lobes will be pointed away from followers). The reason you have to be on the compression stroke is that on the exhaust stroke, the piston will reach TDC again to push the combustion byproduct out of the cylinder and the exhaust valve will be closing and the intake valve will be very near or already opening for the intake stroke.

You can adjust the intake valve just after TDC on the power stroke as you can be assured the intake valve is now closed. Why do you wait until after TDC on the power stroke when the intake and exhaust valve should have both been closed for compression? Good question, because on aggressive cam profiles there can be “valve overlap” which is why on high-performance engines, normally gasoline, you hear what is generally referred to as a “lope” as the exhaust and intake valve opening and closing overlap during low ROM (read low airflow). Once the engine RPM is increased the dynamic airflow comes into effect, usually called the power band, and the overlap is nullified by various pressures and suctions within the engine.

As Tony points out, marking at 120 degrees will give you the full 360 degrees of the engine rotation to move the valves through their various positions.

Finally, a question that normally isn’t answered is why are the intake and exhaust clearances different? The intake valve stem and head are “cooled” by incoming charge air, and fuel in many gasoline engines that are not DI, and the exhaust valve mostly has just exhaust running over it’s stem and head. The exhaust valve will expand more during operation requiring more space between the rocker (or follower) for expansion. This ensures the valve is fully closed during the compression and exhaust strokes. If the valve elongates enough, the valve could stay open and not only allow blow-by, but it would also eventually damage the valve seat.

I hope this helps some others when they go to adjust their valves!

[bluebyu]

Ops and Maintenance manual contains the procedure:
Manual 3810248-08
Can be found on the web or maybe this site.
Procedure is on pages 6-3 to 6-9

Hope this helps

1 user thanked author for this post.

Kevin

[Tony Athens]

Valve adjustment

IMO, and this has been since I was in my teens ( I started on a 4-cyl Renault Dauphine in 1964) ……..Understand how a 4-stroke engine operates and know the firing order– Bar your engine over using a 15/16″ socket/ratchet on the alternator pulley (CW) — learn how easy that works.. It does not matter what cylinder you start at–What matters is understand what is going on..TDC is great but knowing you can adjust an exhaust before TDC and an intake after TDC makes it really easy if you understand how a 4-stroke works–and that is any 4-stroke engine gas or diesel..—————–Use a “marks-a lot” to mark the firing order in front of you & 3 x 120 degrees hash marks on the damper———–Too simple if you understand what is happening
..

1 user thanked author for this post.

Kevin

[Author]

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