# Setting K28 valve timing



## llynrice (Jan 2, 2008)

Recently, I started a thread about my K28 running stiffly in reverse and what I did to fix it. There was no single set of directions for me to follow in setting the valve timing. I used the gear setting write-up in the Roundhouse web site and got help from posts by Jay Kovac and the Bednariks. Now that I've been through the drill, I thought it might be helpful to others who may have to time their engines if I turned what I did into a photo essay. I expect that what I have here would also apply to a K27 and to the K36 (when it comes out). 

I eventually found three problems with my loco which had to be corrected. First, the J-bar was not zeroed. Second, eccentric crank on the engineer's side was not set at the correct angle. Third, the valve on the engineer's side was not positioned correctly on its rod. 

The J-bar problem was my fault and resulted from adjusting the R/C servo incorrectly when I installed the R/C. Once I had readjusted the servo, the linkage moved equally far up and down from the neutral position when I commanded the loco to forward or reverse. If you are using the manual J-bar, it can be centered by loosening the screws that hold the stand in the cab and sliding it backward or forward until the neutral position really is neutral. 

In order to make adjustments to the valves, you have to open up the steam chests. To do that, you have to loosen or remove some details. All of the operations can be done using the nut drivers and allen wrenches provided with the loco (except for one place I'll point out shortly). 

First, remove the four miniature hex head bolts which hold the forward running boards in place. You do not need to remove the running boards. You just need to be able to move them to get at other parts. 










Next, you need to loosen the set screws in the dummy steam pipes. 










Now, remove the row of four hex bolts which attach the wrappers to the cylinders. 










Finally, carefully pull the wrappers off of the cylinders. You will need to move the running boards some and the dummy steam pipes and the wrappers will separate from one another. A lip near the back of the wrapper will likely snag details such as pipes. Just be gentle and you can wiggle the wrappers free. 

With the wrappers off, you can open the steam chest. This is the only place the Accucraft tools did not apply. I used a 5/32" nut driver (very close to 3mm). 










Slide the cover up off the threaded studs and you are ready to begin timing. One caution, on my engine, two of the studs unscrewed partially from the cylinder and their shoulders kept the lid from seating all of the way down at reassembly. Before you put your loco back together, be sure that the studs are screwed in and that their shoulders are below the surrounding surface. 

I'm going to break now to post this much and will follow up shortly with more posts to complete the timing process.


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## llynrice (Jan 2, 2008)

OK. Back again. 

Now that you have opened the steam chests, you can get on with the timing. The slide valves need to be positioned so that they expose the forward and rear steam ports equally as they slide back and forth. 










You can check this by rolling the engine forward with the J-bar set for forward and then rolling it backward with the J-bar set for reverse. There will likely be a small difference in how the forward and reverse settings perform. It pays to favor the forward setting. There is a metal slug on the valve shaft which is locked in place with a set screw and that slug is captured between two ears on the slide block. To center the slide block between to steam ports, unlock the slug and slide it forward or back as necessary and re-lock it. 










On my engine, I found that the valve block on the fireman's side moved about 0.120" back and forth (as measured with a machinist's steel scale) and completely uncovered both ports at the extremes of its travel. On the engineer's side, the valve block moved only about 0.080" and only partly uncovered the steam ports. I loosened the eccentric crank on the engineer's side and adjusted it so that that valve would move about 0.120" also. 

Since then, Jay Kovac told me that he set his eccentric cranks using data from an Aster valve timing instruction. With the piston fully forward in the cylinder, he sets the centerline of the eccentric crank so that it will be 36° above the centerline of the side rods. He told me that he used a protractor to make the measurement. 










When your adjustments are completed, reinstall the valve chest covers. The beveled edges should face out. To avoid distorting the covers, it's a good idea to just lightly snug the nut on one corner, go diagonally to the other corner, back on the the other corner on the same side and then diagonally to the far corner and then repeat the pattern to completely tighten the nuts. 

At this point, you can fire up your loco and test it on rollers. There's no point to putting all of the detail back until you are certain that the valve adjustments are right. I had to open mine back up once and was glad I'd chosen to test it on rollers before buttoning up all of the detail pieces. 

I expect that some of you who have done timing may have some thoughts to add; but, this did work well for me and my engine now runs very smoothly in both forward and reverse. 

Llyn


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## Semper Vaporo (Jan 2, 2008)

The "Angle" you are referencing is not quite the correct place to measure it. The angle should be 90-degrees. But the angle is measured as shown on the drawing below. 
The apex of the angle is center of the axle. One side is the line from the axle to the drive pin and the other side is an imaginary line from the axle to the end of the eccentric rod. 
The angle value you have is only valid on an engine that has the exact same length of eccentric rod and distance of the drive pin from the axle. If, on another engine, either of those distances is different, then the angle you are using will be something other than 36 degrees.


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## llynrice (Jan 2, 2008)

As can be seen from the photo I posted, the eccentric crank angle on my loco pretty well squares with the guideline which Jay Kovac gave me. This morning, I put the loco on the bench and set the main crank pin in the bottom center position per Charles McCullough's sketch and found that the eccentric crank angle meets his criteria, too. So, for the K28, either approach is valid and will work. 

In truth, I received the eccentric crank angle setting data after the fact. While doing the adjustments, I just moved the eccentric crank on the engineer's side so as to make the valve travel as long as on the fireman's side. Hopefully, this thread will help anybody else who needs to improve the valve timing on a K28. 

Llyn


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## lvmosher (Jan 2, 2008)

Love it. Thanks Llyn.


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