Cracked RH4

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comnoz said:
Dances with Shrapnel said:
Glad you posted this as a separate thread because I want to ask - what are the viable remedies other than the obvious "get a Fullauto head".

Would heating up the head and trying to extrude some JBWeld into the crack be a viable patch or just a bodge?

I don't think JB weld would do the trick. There needs to be enough strength to support the valve guide.

I have attempted welding but it took so much heat that everything was crooked when I was done and the head was too soft in the guide area to hold a guide. It machined like chewing gum.

I have a head on the shelf that I have welded up but never did the machining. I figured I would let it set for a few months and see if it got harder with age. It should be hard by now as that was about 10 years ago....

So is it fair to say there is no good remedy for a cracked RH4 head as shown other than to bin it?
 
Dances with Shrapnel said:
comnoz said:
Dances with Shrapnel said:
Glad you posted this as a separate thread because I want to ask - what are the viable remedies other than the obvious "get a Fullauto head".

Would heating up the head and trying to extrude some JBWeld into the crack be a viable patch or just a bodge?

I don't think JB weld would do the trick. There needs to be enough strength to support the valve guide.

I have attempted welding but it took so much heat that everything was crooked when I was done and the head was too soft in the guide area to hold a guide. It machined like chewing gum.

I have a head on the shelf that I have welded up but never did the machining. I figured I would let it set for a few months and see if it got harder with age. It should be hard by now as that was about 10 years ago....

So is it fair to say there is no good remedy for a cracked RH4 head as shown other than to bin it?


1. My opinion on why were the 750 guides 1/2" and 850 upsized to 3/4". Also as to why "upgrading to bronze" instead of 3/4" iron was not ideal either.
The shrink fit of bronze guides causes a squeezing of the guide and reduces the bore size. Now it has a waisted shape. when ever I ream the guides bore It only clears the center of the guide and the extreme tips which might be peened a bit by the tapping home of the guide. In this condidion you can not spot bore guage the hole. Only a full lenght dowel go/no go will approximate the "working" size.
If the guide is clear reamed all the way through the guide will be now "worn out big".

2. Possible bodge/bandaid for cracked RH4 heads. Clean the intake port crack using all solvents possible. gasoline, acetone, brake cleaner, methylene chloride followed by oil contamination removal with compressed air. After drying, seal the crack with "wicking" loctite 290 which is low viscosity and has a possible chance to penetrate and seal. Loctite should have a chance to hold up since the intake port should not be as hot as the exhaust.
Obviously clean the port crack before guide removal if you are going to do that, then repeat after installing new guide, then loctite seal.
 
dynodave said:
1. My opinion on why were the 750 guides 1/2" and 850 upsized to 3/4". Also as to why "upgrading to bronze" instead of 3/4" iron was not ideal either.
The shrink fit of bronze guides causes a squeezing of the guide and reduces the bore size. Now it has a waisted shape. when ever I ream the guides bore It only clears the center of the guide and the extreme tips which might be peened a bit by the tapping home of the guide. In this condidion you can not spot bore guage the hole. Only a full lenght dowel go/no go will approximate the "working" size.
If the guide is clear reamed all the way through the guide will be now "worn out big".

2. Possible bodge/bandaid for cracked RH4 heads. Clean the intake port crack using all solvents possible. gasoline, acetone, brake cleaner, methylene chloride followed by oil contamination removal with compressed air. After drying, seal the crack with "wicking" loctite 290 which is low viscosity and has a possible chance to penetrate and seal. Loctite should have a chance to hold up since the intake port should not be as hot as the exhaust.
Obviously clean the port crack before guide removal if you are going to do that, then repeat after installing new guide, then loctite seal.

Quality bronze guides will be considerably undersize throughout the length both before and after installation. A clean ream job is not a problem with a carbide reamer. A hone finishes the job.
I would not install a bronze guide by applying pressure to the ends of the guide. It will work harden the metal around the hole and make it harder to ream. I install bronze guides with a tool that contacts the flange and pulls them in with a hydraulic cylinder.

I have used locktite 290 on a few jobs with small cracks. It holds for a while -at least until the crack grows larger. Jim
 
Well, you can add me to the cracked RH4 group. I just checked the head on the MK3 that I'm rebuilding, and discovered the dreaded crack at one of the intake guides. Its visible without the need for dye penetrant checking. It looks about 3/8" long, but might be longer if checked properly. Supposedly, the bike had around 20,000 miles when it was torn down and put in boxes, which is how I got it. The other port doesn't show any cracks to the naked eye, and it didn't seem worth it to do the dye penetrant check. Fortunately I have an RH10 head off a race bike that looks pretty good, other than needing exhaust thread repair and stud inserts. More work for comnoz. I have another MK3 that I'm about to tear apart, hoping that the head is ok. Sure would be nice to find a method to repair these heads. Must be a lot of them out there by now. I would consider trying to weld it, but I haven't had really good luck trying to weld on Commando heads, other than for fin repairs. The castings tend to be really porous, and you can never seem to get all the oil out. Those Fullauto heads are looking better and better to me.

Ken
 
lcrken said:
Well, you can add me to the cracked RH4 group. I just checked the head on the MK3 that I'm rebuilding, and discovered the dreaded crack at one of the intake guides. Its visible without the need for dye penetrant checking. It looks about 3/8" long, but might be longer if checked properly. Supposedly, the bike had around 20,000 miles when it was torn down and put in boxes, which is how I got it. The other port doesn't show any cracks to the naked eye, and it didn't seem worth it to do the dye penetrant check. Fortunately I have an RH10 head off a race bike that looks pretty good, other than needing exhaust thread repair and stud inserts. More work for comnoz. I have another MK3 that I'm about to tear apart, hoping that the head is ok. Sure would be nice to find a method to repair these heads. Must be a lot of them out there by now. I would consider trying to weld it, but I haven't had really good luck trying to weld on Commando heads, other than for fin repairs. The castings tend to be really porous, and you can never seem to get all the oil out. Those Fullauto heads are looking better and better to me.

Ken

Bummer, if you can see 3/8th inch without dye then it is probably at least twice that long.
A fix would be nice. I think my cracked RH4 collection is at 13. Jim
 
"Bummer, if you can see 3/8th inch without dye then it is probably at least twice that long.
A fix would be nice. I think my cracked RH4 collection is at 13. Jim"

Looks to me you have enough to practice on.
 
I find the topic of a cracked R4 head depressing. As I read the posts it appears that there is really no fix which is considered "best practice" and permanent other that a Fullauto head of course.

If this is true, I would have to pay over half of the market value of my bike for a permanent fix, and the probability of it happening is fairly high.

Depressing.
 
Diablouph said:
I find the topic of a cracked R4 head depressing. As I read the posts it appears that there is really no fix which is considered "best practice" and permanent other that a Fullauto head of course.

If this is true, I would have to pay over half of the market value of my bike for a permanent fix, and the probability of it happening is fairly high.

Depressing.

If the head was not cracked when the guides were installed at the factory -then the likely-hood of it cracking at a later date is pretty small -unless someone does a poor job of fitting new guides when rebuilding. Jim
 
Thanks Comnoz


I feel much better about the likelihood of my head cracking, and I know now that if anything like valves or guides are needed, I will let a pro do it.
 
How would one detect the kind of cracks we areal king about here in a used bike? In other words, what are the symptoms, in use, of such cracks?
 
Eddie is it possible oil from the rocker compartment can find its way through the crack , then into the cylinder? would a pressure soak of the head in sealing resin seal up the crack ...Norvil do this to "cure" porous heads, so mayby this treatment would do the trick?



Fast Eddie said:
How would one detect the kind of cracks we areal king about here in a used bike? In other words, what are the symptoms, in use, of such cracks?
 
Fast Eddie said:
How would one detect the kind of cracks we areal king about here in a used bike? In other words, what are the symptoms, in use, of such cracks?

A crack presents the same symptoms as a bad valve stem seal -only worse. If the bike is shut off for a few hours and then restarted you will have a lot of smoke from the oil that has leaked into the port. Jim
 
hobot said:
Would the propane torch melt alu repair rods from Muggy Welding have application here?
http://www.muggyweld.com/
Although mapp gas is hot enough to melt the repair rod, what is requires is the material your are heating/repairing to melt the flux and subsequently the rod. Oxy/acetylene is really needed to concentrate the heat to where it is need where you can facilitate the repair before heat disapation. If you can successfully braze a cast iron repair, you can surely handle an aluminum/aluminium repair.
Repairs of this nature are a step up from JB Weld and such repairs should be limited to filling holes, cracks, fins and such, and not for anything requiring structural integrity. Just sayin.
 
+1 Pete, seen this process at the bike shows, the guy welded up a hole in a coke can :?: big deal!!! It was called Lumiweld.


pete.v said:
hobot said:
Would the propane torch melt alu repair rods from Muggy Welding have application here?
http://www.muggyweld.com/
Although mapp gas is hot enough to melt the repair rod, what is requires is the material your are heating/repairing to melt the flux and subsequently the rod. Oxy/acetylene is really needed to concentrate the heat to where it is need where you can facilitate the repair before heat disapation. If you can successfully braze a cast iron repair, you can surely handle an aluminum/aluminium repair.
Repairs of this nature are a step up from JB Weld and such repairs should be limited to filling holes, cracks, fins and such, and not for anything requiring structural integrity. Just sayin.
 
Lumiweld etc can work well. When I used it, you had to scrub the surface with a stainless steel brush prior to melting the rods onto the surface, then, with the product still molten, you had to score through it with a sharp stainless steel rods to properly 'tin' the surface.

When I think about that, and if the process is still the same, it makes me think that it would be impossible to get the molten rods to be properly 'drawn' into the crack, and even if it did, it would not 'tin' properly at all.
 
Dances with Shrapnel said:
comnoz said:
Dances with Shrapnel said:
Glad you posted this as a separate thread because I want to ask - what are the viable remedies other than the obvious "get a Fullauto head".

Would heating up the head and trying to extrude some JBWeld into the crack be a viable patch or just a bodge?

I don't think JB weld would do the trick. There needs to be enough strength to support the valve guide.

I have attempted welding but it took so much heat that everything was crooked when I was done and the head was too soft in the guide area to hold a guide. It machined like chewing gum.

I have a head on the shelf that I have welded up but never did the machining. I figured I would let it set for a few months and see if it got harder with age. It should be hard by now as that was about 10 years ago....

So is it fair to say there is no good remedy for a cracked RH4 head as shown other than to bin it?

Bore out the inlet port all the way to the bowl. Insert, press or weld in heavy wall tubing. This gives you new material for the guide area and also gives you the opportunity to raise the port. Requires machining a new valve guide bore. Sounds like lots of work but it is doable (and is being done presently).
 
Is there a reasonable cost benefit to machining a repair vs new Fullauto head, fully populated and ready to install?
 
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