Cracked RH4

Status
Not open for further replies.
comnoz

comnoz

Joined
Dec 10, 2008
Messages
7,253
Country flag
This is the best picture I have ever been able to get of a classic cracked RH4 so I thought I would post it here.
Note that this crack was not visible to the naked eye. It was not until i heated the head with UV dye that I got it to show up.

Cracked RH4
 
Ouch.
Is this the stock port size, or have they been opened out some ?
 
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?
 
Rohan said:
Ouch.
Is this the stock port size, or have they been opened out some ?
Click to expand...

It is a stock head. It was removed from a new bike that was smoking. There was supposedly about 200 miles on it. Jim
 
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?
Click to expand...

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....
 
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?
Click to expand...

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....
Click to expand...


Really interesting & worrying at the same time :roll: :roll:

If your head was cracked in this place would you have any idea from fitting the guides that the crack was present? i.e. would the guide go in super easy or would it move slightly?

You said the bike was smoking, are we talking about a James Bond getaway smoke screen or something more subtle?
 
comnoz said:
This is the best picture I have ever been able to get of a classic cracked RH4 so I thought I would post it here.
Note that this crack was not visible to the naked eye. It was not until i heated the head with UV dye that I got it to show up.
Click to expand...

Were you unable to get a positive with a normal dye penatrant test?

comnoz said:
It is a stock head. It was removed from a new bike that was smoking. There was supposedly about 200 miles on it. Jim
Click to expand...

This sounds very familiar to what happened in about 2003 when I discovered and reported this phenomenon of cracked RH4's. One of the two cracked heads was reported to be a very low mileage, almost a new head, and WAS cracked.
http://atlanticgreen.com/nhth.htm

It is for this reason also, I will check my 7 mile MKIII RH4 head for a crack. I sincerely believe this is a factory induced problem. We shall see.
 
dynodave said:
Were you unable to get a positive with a normal dye penatrant test?
Click to expand...

It was easy to get a positive with just a little spray crack finder.

Getting a picture of it was the harder part. That is why it is showing up a little different.

I put a coating of dye in the port and then I put a few drops of solvent in the spring seat area and warmed the head. The solvent came through the crack and washed the dye away leaving the black line which did show with a camera.

It also showed the crack was longer than I could see just using the spray crack finder. Jim
 
dynodave said:
It is for this reason also, I will check my 7 mile MKIII RH4 head for a crack. I sincerely believe this is a factory induced problem. We shall see.
Click to expand...

I don't think there is a doubt that it was a factory induced problem. The combination of the 32mm port and the larger 850 guide makes for a pretty thin section of metal on the carb side of the guide.

If the factory or anyone else fits a guide with more than about .0015 interference fit -there is not enough strength to prevent a crack. Jim
 
click said:
Really interesting & worrying at the same time :roll: :roll:

If your head was cracked in this place would you have any idea from fitting the guides that the crack was present? i.e. would the guide go in super easy or would it move slightly?

You said the bike was smoking, are we talking about a James Bond getaway smoke screen or something more subtle?
Click to expand...

That depends on how long the crack is. The one thing I have noticed if I try to put a guide in a head with a crack is that the guide goes in with a small angle and does not align well with the seat.

A crack there presents just like a bad valve stem seal. Heavy smoke for a couple minutes after a restart. Just a little extra smoke after that. Jim
 
Matchless said:
What's the reason for 850 guides being a larger dia. than 750 guides ?
Click to expand...

I really don't know other than possibly the fact that iron 750 guides are a bit fragile and sometimes came loose in the head.

Moving up to bronze guides would have been a better but more expensive cure. Jim
 
Looks like another area where the accountants overruled the engineers. The story of British industry sadly.
 
macthless, that is a shallow point of view to reflexly claim Brit short cuts were d/t to internal management only and not them having to respond to much larger pressure of the Banksters in The City and their hired Parliament. Its surprising how well Brit Industry did compared to rest of the world in those conditions. Otherwise only rational conclusion is conspiracy of Brit motor industry to piss off customer to buy foreign.
 
hobot said:
macthless, that is a shallow point of view to reflexly claim Brit short cuts were d/t to internal management only and not them having to respond to much larger pressure of the Banksters in The City and their hired Parliament. Its surprising how well Brit Industry did compared to rest of the world in those conditions. Otherwise only rational conclusion is conspiracy of Brit motor industry to piss off customer to buy foreign.
Click to expand...



This should have it's own thread really, but I saw a TV interview with Hugh Palin who was head of the MC industry body in the 60s. The interviewer asked:

"Aren't you worried about the Japanese motorcycles taking your market share"

Palin: " Oh no, the Japanese only build small motorcycles, and when kids have passed their test on a small bike, they buy a bigger bike like a Triumph or Norton."

The whole management was useless. The British car industry is doing quite well, but it's all been sold to BMW, Tata etc because the British management couldn't run the industry. ( Spoken as a Brit ).
 
I've posted references in other threads to back up my sad summary but reason I bring it up is even though we know company management had their head up in the clouds per your quote - that is more stuck in a rut to improve on products - BuT not evidence of intentional bad parts or designs produced. Someday we'll have a bandaid like patch ya shine a laser on that merges the thin patch with the base alloy stronger than original. So was Norton head weakness & guides on purpose or just over sight?
 
We are drifting here! :roll: Getting back on track. :arrow: You know that railroad train that doesn't go south.
I am going to throw a little mix into the cauldron of RH4 soup that is posted here. If there are no cracks in your RH4 and you want to tighten up the valve to guide tolerance. Would you
1. Pull the guides and install bronze guides and hope not to crack the inlet tunnels or,
2. Ream out to oversize valve shaft diameters or,
3. Bore middle of cast iron guides and install bronze inserts to the original guides?
Inquisitive minds need to know. :idea:
Regards
Thomas
CNN
 
CanukNortonNut said:
We are drifting here! :roll: Getting back on track. :arrow: You know that railroad train that doesn't go south.
I am going to throw a little mix into the cauldron of RH4 soup that is posted here. If there are no cracks in your RH4 and you want to tighten up the valve to guide tolerance. Would you
1. Pull the guides and install bronze guides and hope not to crack the inlet tunnels or,
2. Ream out to oversize valve shaft diameters or,
3. Bore middle of cast iron guides and install bronze inserts to the original guides?
Inquisitive minds need to know. :idea:
Regards
Thomas
CNN
Click to expand...

I install new bronze guides in RH4 heads all the time. I just make sure the interference fit is in the .0010 to .0013 range and pull them in straight. Bronze guides will stay put with less interference than the cast iron guides due to the closer expansion rate. Jim
 
Status
Not open for further replies.
Back
Top