suspect cracked head

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hershey

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Bought a mk3 this past spring at an estate sale of a friend I use to work with. The bike smoked from both cylinders but a lot more on the left side. Tore the motor down and found the cylinders were both pitted, rebored .020 and installed new rings and pistons.Inspected the head all valve guides are in very good condition , valves themselves in very good condition. I hand lapped the valves and planed the head just enough to make sure it was flat. Rebuilt the motor and fired it up and found that the left cylinder smoked as much as before the rebuild. The right cylinder is smoke free. I remember my friend saying years ago that the left cylinder always did smoke. I understand that the RH4 head is prone to cracking and allowing oil into the cylinder. Does anybody know where the RH4 commonly cracks so I,ll know were to check for the crack. thanks hershey
 
I believe it is around the valve guides allowing oil to seep into the cylinder, but others here will be able to more accurately help you out.
 
The RH4 normally cracks on the carburetor side of the intake valve guide.
You may be able to see it by just removing the carb and looking down the port. Sometimes it takes a dye test. Jim
suspect cracked head
 
I also had a smoking cylinder on my 850. Stripped top end off and fitted new piston rings, removed the pistons more for something to do than a real cause. Anyway, put it all back together with new wrist pin circlips . Started it up and left cylinder smoked like a trooper. Took it apart again and a circlip had come out and tram lines the bore. It was then I found out about the wrong size circlips being included !
sam
 
Yes RH4 are crack prone. I had documented my research... now 19 years ago
From my website article : http://atlanticgreen.com/nhth.htm
http://atlanticgreen.com/nhth.htm
Norton Heavy Twins Heads
David Comeau-Aug 2000

"It has recently become apparent that the thin intake port wall under the spring perch results in a very high percentage of RH4 heads being cracked at one or both guides. A simple dye penatrant test reveals this unfortunate reality, which evades detection by a casual glance into the port."

My advise to all is... absolutely every RH4 head that comes off an engine should have a dye penatrant test done with the valves removed. Very very few have the visual acuity to see the crack from the port without the aid of the dye. Only about 50% of the heads I tested were OK.
 
comnoz said:
The RH4 normally cracks on the carburetor side of the intake valve guide.
You may be able to see it by just removing the carb and looking down the port. Sometimes it takes a dye test. Jim
View attachment 12238
Click to expand...
Jim do you still do work on norton heads? You checked another RH4 head for me a few years back, it turned out okay, but the one I have now I feel sure it has a major crack. Oil even weeps out the exhaust port threads and blows back the side of the bike when ridding. Can most cracks be repaired or would it be better to just try and find another head? Thanks Jack
 
hershey said:
Jim do you still do work on norton heads? You checked another RH4 head for me a few years back, it turned out okay, but the one I have now I feel sure it has a major crack. Oil even weeps out the exhaust port threads and blows back the side of the bike when ridding. Can most cracks be repaired or would it be better to just try and find another head? Thanks Jack
Click to expand...

Jack,
I work on Norton heads every day.
The crack in the intake port is difficult to repair and it is usually better [more economical] to find a used head.
I can test it and let you know what I would recommend. Jim
 
comnoz said:
Jack,
I work on Norton heads every day.
The crack in the intake port is difficult to repair and it is usually better [more economical] to find a used head.
I can test it and let you know what I would recommend. Jim
Click to expand...
Thanks Jim I,am going to remove the head the first of next week and see if I can see the crack. I,ll get back to you next week. If I can see a crack in the intake tunnel would you have or would you know where I could purchase another head. Thanks Jack
 
hershey said:
Oil even weeps out the exhaust port threads and blows back the side of the bike when ridding.
Click to expand...
I've recently had these symptoms on a T160 after exhaust valve guide replacement. It turned out to be the guide had snagged on fitting and there was a small channel for the oil to get into the exhaust port, hence oil on the front of the engine from the port and some smoking from the exhaust. So I'd have a look at the exhaust port / valve guide as well and see if it's wet with oil there.
 
Thanks I,ll check the guides out when I remove the head . Everything looked okay when I had the valves out to hand lap them and I did install new valve seals but then again I wasn,t looking for cracks or leaks in the head I figured the rebore and new pistons would take care of the smoking. Does anybody have a RH4 head or know where I could purchase one if I find mine is cracked in the intake tunnel.There is one on ebay but it has been planed down into the first fin. I don,t know if that is too much stock taken off. Thanks Jack
 
dynodave said:
Yes RH4 are crack prone. I had documented my research... now 19 years ago
From my website article :
http://atlanticgreen.com/nhth.htm
Norton Heavy Twins Heads
David Comeau-Aug 2000

"It has recently become apparent that the thin intake port wall under the spring perch results in a very high percentage of RH4 heads being cracked at one or both guides. A simple dye penatrant test reveals this unfortunate reality, which evades detection by a casual glance into the port."

My advise to all is... absolutely every RH4 head that comes off an engine should have a dye penatrant test done with the valves removed. Very very few have the visual acuity to see the crack from the port without the aid of the dye. Only about 50% of the heads I tested were OK.
Click to expand...


Please excuse my dumbness, but are there alternatives to the RH4 for 850's ? If not, is there any point in buying a second hand head which may have the same issue ? Are there any realistic fixes for these cracks?


Cheers,

cliffa.
 
I’m looking for a 750 head also, tired of screwing with mine. Like to find one crack tested (dye check) valves, guides, seals. I’ve had mine off 3 times and still right cyl smoke occasionally.
 
cliffa said:
Please excuse my dumbness, but are there alternatives to the RH4 for 850's ? If not, is there any point in buying a second hand head which may have the same issue ? Are there any realistic fixes for these cracks?


Cheers,

cliffa.
Click to expand...

Yes, the RH10 head is an alternative that doesn’t appear to have the same tendency to crack. It also has better ports.

A 750 head can be converted too, but that’s a bit of extra work.
 
cliffa said:
Please excuse my dumbness, but are there alternatives to the RH4 for 850's ? If not, is there any point in buying a second hand head which may have the same issue ? Are there any realistic fixes for these cracks?


Cheers,

cliffa.
Click to expand...

There are basically 2 interchangeable 850 heads. RH4, 32mm port,was used in 73 and 75. RH10, 30mm port was used in 74.
See here: http://atlanticgreen.com/nhth.htm
Unless you have a source for a NOS norton head from 50 years ago, you are taking one off a bike...
FWIW, I have not personally seen a cracked RH10 though I have tested several.
Laser welding sounds like a viable solution. My uncle did laser welding a long time ago for a big corporation, but finding someone in the USA, today, may be difficult or very expensive.
 
dynodave said:
There are basically 2 interchangeable 850 heads. RH4, 32mm port,was used in 73 and 75. RH10, 30mm port was used in 74.
See here: http://atlanticgreen.com/nhth.htm
Unless you have a source for a NOS norton head from 50 years ago, you are taking one off a bike...
FWIW, I have not personally seen a cracked RH10 though I have tested several.
Laser welding sounds like a viable solution. My uncle did laser welding a long time ago for a big corporation, but finding someone in the USA, today, may be difficult or very expensive.
Click to expand...

When one of the alternative is a Full Auto head is laser welding really that expensive?

Anyone want to send me a cracked head and I can take it to this place to see what they say.

https://www.lafargeandegge.com/welding/

There is several high tech metal companies in this area, most notably Precision Castparts. There are several others that specialize in unique and specialized metal tech due to the high tech businesses such as Intel.
 
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Thanks all for the answers. I suppose that RH10 heads are rarer than a rare thing now?

Rumor has it that there may be more Fullauto type heads available in the future - any truth in that ?

Cheers,

cliffa.
 
comnoz said:
Jack,
I work on Norton heads every day.
The crack in the intake port is difficult to repair and it is usually better [more economical] to find a used head.
I can test it and let you know what I would recommend. Jim
Click to expand...

i take it the crack is letting oil into the port
and possibly the guide is fairly loose when the casting is up to operating temp

is the acess so bad it cant be welded ?
how about the old fashioned method of drilling and tapping to accept small soft brass or copper studs coated in retainer , with a,50 percent overlap leave them slightly long
then peen the ends and flush off the exess , it works on cumbustion chambers so its worth a go
 
In the past I was supplied with valve guides that were tapered
They were wider at the bottom of the guide and appeared to be tight in the head but it smoked really badly
I finally diagnosed what it was and took the guides back to the shop
I went through their stock with my micrometer until I found a set of completely parallel guides
Once fitted the engine was smokeless
I must add this was on a 750 combat
Cheers
 
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