Valve guide geometry

[martanke]

Hi,

I am doing a full rebuild of a Chrysler Royal M8 marine engine, a 323.5 cu in flathead straight 8. Apart from the externals it is very similar to the automobile version straight 8 and most internals are exactly the same. Cooling system is quite different though. Based on the engine's serial number plate I believe it's a 1946 model but several parts have been replaced over the years so I'm not sure what year the block is. I have it all torn down except for the valve guides which won't budge, I will let the machine shop take care of those. Replacement guides are available from many sources but I have a few questions that I'm hoping someone here can help me with.

1. My engine manual (see photo attached) says to install all the guides in the same way: "Start the guide in the hole with the tapered end up." But in the manual for the Royal M48 which is the successor to the M8, it says to install the intake guides this way and the exhaust guides with the tapered end down. It is my understanding that the car engine manuals also differentiate between intake and exhaust. The guides that are currently in my engine are installed per the "newer" instructions (every other tapered up/down). Why did Chrysler change the geometry like this? Why are they tapered to begin with? And why should the guide to top of block distance be larger for exhaust than intake?

2. I think my machinist may end up drilling out the old guides, which would leave a slightly larger hole than standard. Are there oversize guides to be found somewhere? Or will I have to make a custom guide?

Thanks 

[Bryan]

I would have the guides installed per newest manual. It is intake one way, exhaust the other.  The guides are not drilled to get them out. They don't come in larger outer diameters. They are pressed out, or impact driver with a special tool end driven out, or using a 5/16-24 grade 8 bolt and socket to press out.  Look at my post, had a hard enough time with them.   https://p15-d24.com/topic/56535-rear-oil-galley-plug-idea-pulling-motor-on-1948-dodge/?do=findComment&comment=619125

 

[keithb7]

I am no engineer, but I'll guess at a few points.

The intake guides, the cylinder vacuum pulls air across them in 1 direction only. From the carb, and down into the cylinder. The exhaust guides have exiting gasses from the cylinder cross over them in the exact opposite direction as the intakes. I might guess the guides are installed in opposite direction due to air flow. Intake in, exhaust out. Perhaps someone smarter than me can tell us what the tapered end of the guide is designed to do. Does the taper help negate a vacuum or venturi effect on the inside of the guide to maybe prevent crank case vapours from entering the cylinder?

 

 

 

Edited February 22, 2022 by keithb7

[Bryan]

1 hour ago, keithb7 said:

I am no engineer, but I'll guess at a few points.

The intake guides, the cylinder vacuum pulls air across them in 1 direction only. From the carb, and down into the cylinder. The exhaust guides have exiting gasses from the cylinder cross over them in the exact opposite direction as the intakes. I might guess the guides are installed in opposite direction due to air flow. Intake in, exhaust out. Perhaps someone smarter than me can tell us what the tapered end of the guide is designed to do. Does the taper help negate a vacuum or venturi effect on the inside of the guide to maybe prevent crank case vapours from entering the cylinder?

 

 

Yeah, yeah..it's so easy.. ? ??

[martanke]

Bryan, Keith,

Thanks I've seen the video and read the post, all very instructive. My guides are definitely of the defiant type. I don't have an impact driver but my big hammer didn't move them at all. Will try the threaded rod approach. My concern is that drilling out the valves could be the last resort if they're really stuck and in that case it seems like I have to make custom new ones.

 

I would think the tapered end up should improve flow on both exhaust and intake, it seems like many flathead builders are trimming down the guides in conjunction with porting. Maybe the non-tapered end provides more mass to cool the exhaust valve? But then again there's more guide mass sitting right in the hot exhaust flow. Hmm.

[Bryan]

I'll either leave them alone, or just shorten the intake ones.  The exhaust guides, I'm worried about heat absorption into the block away from the valves, wouldn't want to mess with that.  With the screw method that's the only thing that worked for me.  I was shattering the tops with the air hammer.  Important is when you get the guide moving, if it stops again, check that it's not hitting the larger socket you have under it to draw the guide into.   Anything that is larger than the guide that fits up under it can be used.   I had to sometimes use progressively smaller washers (from large to small) sometimes on the nut at the bottom to keep it from being drawn up into the socket. Good luck.

[martanke]

Wel the guides are out, ended up using a hydraulic press. After cleaning and magnafluxing the block I have discovered a couple of pretty bad freeze cracks. I knew of two that I was going to fix using the lock-n-stitch method, but now I'm up to four cracks, some of which are in pretty bad places.

So now I'm looking for a good engine block. The marine and automobile versions are the same as far as I know and any 323.5 cu in from 1946-50 should work. Does anyone know of one?

Thanks

[Dodgeb4ya]

MyMopar has Vol.3 #3 "The Story of Valves" film on the valves/guides and why they are made the way they are etc....and proper installation.

I have a couple 323's straight eight engines...Seattle

PM only for more info.

 

Edited April 8, 2022 by Dodgeb4ya

[martanke]

Thanks for the tip, I will check out the film. And I will PM you about the engines.

[rallyace]

The valve guides are installed to better control the heat transfer from the valve stem. The intake valves are cooled by the intake charge, the exhaust valves do not have this cooling as they see all of the heat from the charge.