How to repair valve guide boss

-
4spdragtop

4spdragtop

FABO Gold Member
FABO Gold Member
Joined
Aug 28, 2009
Messages
39,464
Reaction score
22,740
Location
Ontario Parts Unknown
Was taking cyl head #2 apart, and discovered this crack. This is 2nd crack now, 1st one was on other head and in bowl area.
This one looks worse. These heads were freshly machined 25 years ago and have been bagged and stored.
This crack hasn't migrated any deeper than where the seal starts.
I'm thinking maybe an epoxy of some sort?
Suggestions?
Thanks
20190411_184945.jpg
 
That happens a lot installing new guides. When I was doing head work and installed new guides, I milled the top of the old guides OFF. It's not a "guide boss" but just the top of the factory guide. There's absolutely ZERO need for it to be there. You can mill them off with the appropriate guide cutter (whatever the OD of the new guides are) and run a positive seal that will install tightly around the new guides.

That's how "I" would do it.
 
Yeah that's what I read in regards to crack in bowl area. Crack wasnt near as big as this one though lol.
Heres pics of seal style I'm using. Can I use same style but with an ID to match the OD of the guide? This is assuming that the guide itself is left untouched in the machining process.
Thanks!
RustyRatRod said:
That happens a lot installing new guides. When I was doing head work and installed new guides, I milled the top of the old guides OFF. It's not a "guide boss" but just the top of the factory guide. There's absolutely ZERO need for it to be there. You can mill them off with the appropriate guide cutter (whatever the OD of the new guides are) and run a positive seal that will install tightly around the new guides.

That's how "I" would do it.
Click to expand...

20190411_211530.jpg


20190411_211617.jpg
 
Yup. You can use that same style but match the OD of the guide. The cutter might barely skim it, but it won't remove enough the seal will fit loosely.
 
It would likely not crack any further, but if your luck is like mine, it would crack, break off and fall on top of the camshaft. Game over. Anybody else could run it like that for 100K.
 
Put a hose clamp around it. JK you can have a new guide pressed if you want, but that wont hurt much if removed.

20190411_192332.jpg


20190411_192327.jpg
 
Last edited:
he already has anew bronze guide inside the factory one
what RRR said
machine all the factory ones down to the spring seat and run viton seals
what's the od of the new bronze guide
old rubber seals are junk after 25 years even if not run
viton cost about two orders of magnitude than rubber- silicon is just slightly more than buna-n / butyl compared to viton which is the premium stuff
 
New guides in both heads. They arent pressed inside old ones as you mentioned?? Maybe I misunderstood?
Seals currently on it are Vitons I thought? On intake valves. Exhaust have new umbrellas.
Wyrmrider said:
he already has anew bronze guide inside the factory one
what RRR said
machine all the factory ones down to the spring seat and run viton seals
what's the od of the new bronze guide
old rubber seals are junk after 25 years even if not run
viton cost about two orders of magnitude than rubber- silicon is just slightly more than buna-n / butyl compared to viton which is the premium stuff
Click to expand...
 
The first picture is a bronze guide pressed into the original iron one. It's one way to replace them. It's fine to run that way, and cracking is common when it's done in that manner. A performance shop would have removed the iron guide boss, and run the better positive seals.
 
Wyrmrider said:
he already has anew bronze guide inside the factory one
what RRR said
machine all the factory ones down to the spring seat and run viton seals
what's the od of the new bronze guide
old rubber seals are junk after 25 years even if not run
viton cost about two orders of magnitude than rubber- silicon is just slightly more than buna-n / butyl compared to viton which is the premium stuff
Click to expand...
Yes captain obvious..
I'm talking about cutting the cracked shell off in the outside aka what left of the as cast guide. Thought I'd show people the guide that is sometimes used in their heads, mostly people slip in k liners... or steel guides for stocker stuff... they last.
 
Last edited:
moper said:
The first picture is a bronze guide pressed into the original iron one. It's one way to replace them. It's fine to run that way, and cracking is common when it's done in that manner. A performance shop would have removed the iron guide boss, and run the better positive seals.
Click to expand...
Exactly.
 
Since the heads are off and apart use a guide top cutter and machine the cracked guide boss from around the new bronze guide and get some new seals to match.
 
those cracked old guides usually do not break off
usually
but find the seals in the new size you need before machining
 
Thanks guys, I new the valve guides were new. I assumed factory used bronze as.well?? I'll take them to machinist and get him to remove the cracked ones. Should the guide be cut down as well? I would assume so ...but?
Thanks all.
 
The factory “guide” is just a hole drilled in the iron.
What you have are bronze repair sleeves installed.
The original guide bore is drilled and reamed, and the repair sleeve is pressed in.
If the reamer is cutting to a slightly small finished size(getting worn out), there is a little more press on the new repair sleeve....... and you end up with a cracked boss.
Sometimes they just crack even when everything is “right”.

The guide top needs to be short enough to provide adequate clearance between the retainer and the seal for whatever lift cam you’re going to use.
I like to have about .100 clearance, but .060 is adequate.
I prefer to have a little extra in case there’s a cam swap to something with a little more lift at some point in the future.
 
If these bronze guides or even K-line inserts are new do not change them
just double check the clearance
as said above this procedure when used with solid bronze guides can crack the original cast iron- usually not a problem
if the clearance is off too loose or too tight then machine off the cast iron after you have new seals the right size for the bronze guide (after machining if necessary for size or retainer clearance)
I would knurl the new guides for oiling and refinish/ resize
I also od hone the valves- especially new ones as some have a finish that acts like a round file on your new guides- the hone helps holding oil and teh knurl supplies oil
welcome to unleaded gas
 
Wyrmrider said:
those cracked old guides usually do not break off
usually
but find the seals in the new size you need before machining
Click to expand...

Usually not. But if those were my heads, them sumbitches would break off, fall into the engine, take the cam out on their way to gettin sucked up by the oil pump. Jes sayin. lol
 
Hi, I just came across this thread and I have a similar issue (as per photos).

So as plainly as you can explain it, what's the best way to repair these?

The guy rebuilding my engine was going to scrap my heads and use replacements, but I think my existing heads are a higher spec.

IMG-20220722-WA0002.jpg


IMG-20220824-WA0011.jpg
 
Lot's of rebuilt heads in use, with cracks like that in them..
 
Indiges said:
Hi, I just came across this thread and I have a similar issue (as per photos).

So as plainly as you can explain it, what's the best way to repair these?

The guy rebuilding my engine was going to scrap my heads and use replacements, but I think my existing heads are a higher spec.

View attachment 1715980350

View attachment 1715980351
Click to expand...


Find a new machinist. It looks like it has a false guide in there already. Press it out, press a new one in there. It ain’t hard.
 
Indiges said:
Hi, I just came across this thread and I have a similar issue (as per photos).

So as plainly as you can explain it, what's the best way to repair these?

The guy rebuilding my engine was going to scrap my heads and use replacements, but I think my existing heads are a higher spec.

View attachment 1715980350

View attachment 1715980351
Click to expand...
If a shop was going to scrap your cylinder heads due to those valve guide cracks, that shop is telling you they are either
1) don’t have a clue what they are doing
2) only after your money
And in response you should take your work elsewhere.
 
And i learned something!
Lots of smart guys here on FABO!!
 
You must log in or register to reply here.
-

Back
Top