The Stovebolt Site Forums The Shop Area Engine Shop cracks in valve guides

Hello,

I have a '54 235 block with 848 head in my '54 Chevy. It was "professionally rebuilt" about 3000 miles ago, but I think a better description might be "bare mininum to get it out of shop". Anyway, I recently lost compression on cylinders 2 and 3. Removed head and found the copper Fel-pro head gasket was blown between cylinders 2 and 3. The engine has always smoked at idle, so I figured that I best inspect and replace the valve stem seals while the head is off. In this process, I noticed the exterior of some valve guides are cracked.

Is this common, and do they need to be replaced?

I have tried the search function and did not come up with much. I have been doing a lot of reading here lately trying to familiarize myself with the in's and out's of these engines.

Thanks!

Yes, and it would probably be the best idea to replace all the guides while you're at it. Also get the head resurfaced- - - -it's unusual for a gasket to blow if the head and block surfaces are flat within less than a couple of thousandths. It's best to core-drill the guides to leave only a thin shell before trying to drive the old ones out- - - -you really don't want to crack the head in the process of changing the guides. Stovebolt guides are 5/8" in diameter- - - -0.5625". I have a 7/16" drill bit with the first 3/4" ground down to 11/32" to use to thin the guides and stay on center.
Jerry

Edit: Asking "car questions" on Stovebolt will probably get you 40 lashes with a wet noodle by a moderator. It might be a good idea to keep engine questions generic, as to the vehicle it's in.

Thank you!

Are the aftermarket guides (SBI and Qualcast) suitable?

I have a lot more reading to do.

I used to travel to Lincoln Co TN often for work. Very nice place and lots of good people.

My calculator must be broke. It says 5/8" = 0.625"

More info after further inspection. The machine shop used bronze/brass inserts in the valve guides. I am guessing that was the safe move at the time that avoided possible damage to the head if the guides were stuck.

I wold guess they drilled out the original guide and put new bronze guides down the middle of the originals. Post a picture of your head.

Hahaha! HRL must have fat fingered the keyboard.

That is exactly what I do. A good number of years ago, I had an 848 head that was giving me a difficult time getting the original cast iron guides out. One in particular. But I was determined. I was going to get that guide out. Right up to the moment I caused a crack in the head pounding on the guide. Turned a completely usable 848 head to into a boat anchor. So from at least the 1980s I have always drilled the guide out to use a bronze liner. Then machine the top of the guide for a Teflon seal. So if your guides are already prepared for a bronze liner, you may just be able to remove what's left of the bronze liner and install a new one.

I've used dozens, if not hundreds of bronze guide liners. They're OK for a quick repair, but if a guide is pressed into the head like on a stovebolt it's simpler to just change the whole guide. Thinning the original guide and using an air hammer with the right sized driver gets it moving pretty easily. I do the bronze liner method on Chevy and Ford V8s that have the guides cast into the head.
Jerry

Well, you and I will have to respectfully disagree on that as I have been using them for my high performance heads for 45 years, lol. So in my view, they are more than just ok. I just ran a 261 I built in 2015 at the trifive nationals. Ran the motor to 5800 rpm multiple times, multiple runs, as I have at every trifive nationals since 2015. In fact, I won the street tire class this year. That motor has to have near 100 runs on it. Yep, bronze liners.

I happen to believe that the bonze helps the lubrication of the valve stem, using less oil (and teflon seals) then just teflon seals and cast iron guides. I have no empirical data to support my belief other than I have built dozens of these motors and all used the bronze liners and not one single issue.

That being said, I don't think there is anything whatsoever wrong about using new cast iron guides. I just prefer the bronze liners.

My friend owns the machine shop that I use. This is his son drilling out and installing a set of liners for one of my 848 heads. This is from a couple of years ago but you can get the jist of the procedure.

Actually, I just checked- - - - -the decimals were right- - - -the fraction was wrong. Stovebolt guides have a 9/16"OD, not 5/8"!

On race engines, I bore the cast iron guides out and install full thickness bronze ones. I just don't do race stuff on street engines- - - - -I got over doing that kind of work just for the brag factor a long time ago. However, I'm not against taking somebody's money if they insist on it- - - -once I've expressed my opinion.

www.ebay.com/itm/321311845582?

Jerry

This is actually a great topic at this point, I have an "848" head cleaned up and prepped for the machine shop. I had planned on having the valve guides replaced with Bronze as well as a few other tweaks. I had a set of 327 heads prepped this way a number of years ago and have had no issues. I figure it's just good insurance.

Just to be clear, I am not replacing the cast iron guides with bronze guides. The original cast iron guides are left in place. The worn original guide is corrected by drilling through with a pilot drill. You are only removing a small amount of metal but this corrects the guide for straightness. In other words, makes a nice round straight hole through the guide.

Once the original cast iron guide is corrected for straightness and slightly enlarged to accept the liner, the bronze alloy liner is installed. The liner is then reamed to fit the valve stem to provide sufficient clearance between the guide and valve stem. You want enough clearance for some amount of oil to lubricate the guides and valve stem. Once the liner is installed, reamed to size, the nice straight guide is the basis for the valve job. Everything pilots from the guide.

For me, the bronze liners do not require a lot of excessive oil for lubrication so between the bronze liners and the newer style Teflon seals, I can do a better job with oil control down the valve stem then what the little stock type O rings do (and those things fall apart abut 30 minutes after you install them) and thus keep excessive oil from the combustion chamber and tailpipe.

The cast iron guides, in my opinion, they need a bit more oil for cooling and lubrication. So if using a Teflon seal, the machinist has to make sure the clearance is not too tight, erroring on the wider side for the guide, stem and seal, just to make sure not too much oil, just right, to avoid excessive oil in the combustion chamber.

Many ways to tackle rebuilding a 848 head. Some good some not so good. This just happens to be how I do mine. Maybe my way is not so good, lol. Truth be told though, I zing my 235 and 261 motors pretty good and have done so for many many years, like 48, lol. So I stick to what works for me.

Craig, the problem will be finding bronze guides long enough, and big enough diameter to fit a stovebolt head. Stovebolt guides are longer, and larger diameter than the guides used on small block V8 heads- - - - -by a considerable amount. I was making a living as an engine builder and machinist when the bronze guide liners came onto the market, and they made a big splash back then. They have fallen out of favor in the past 20-something years, which is why there are thousands of them available on sites like Ebay from the surplus sellers. Yes, they work- - - - -no, they're not profitable for use in a high volume machine shop with the equipment to bore a head for replacement guides. There's just too much labor time involved in reaming a guide, installing a liner, reaming again, and finally doing a valve job once a worn guide is repaired.
Jerry