Cracked head?

If any of you read it, I had a thread going about trying to get my Amal premiers to idle. At the end of the thread I thought I had found an issue with the head. I figured I should start a different thread for this. The problem that I am having is with getting a consistent idle. I was spraying carb cleaner around to find an air leak and noticed something. When I put the nozzle in the nook in the head behind where the intake manifold bolts up and spray, the engine instantly dies. I sprayed the insulated gaskets between the head and intake and that didn't have the same effect. I have attempted to add a picture of the nook. Do you think it's a cracked head? It is higher than the head gasket. Both cylinders have compression of 140 warm/130 cold. I am already upside down on this bike and don't have a ton more money to spend on an engine repair/rebuild.
Josh

Is that a crack in the RH manifold?

If it's not a cracked manifold, I wonder if it's just a porous casting between the port and fresh air?

I thought the manifold might be cracked also, but spraying there doesnt make any changes. If it is a porous spot on the head, i suppose I will need to have it welded before i get a smooth idle.
Josh

Les, isn't that the casting mark?

swooshdave said:

Les, isn't that the casting mark?

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Yes, casting line.

You need a better photo using a light. When all is said and done you may need to pull the head for inspection. No biggie , kinda fun.

Bowtoy70 said:

.......... I am already upside down on this bike and don't have a ton more money to spend on an engine repair/rebuild.
Josh

Click to expand...

Unfortunately that seems to be "the nature of the beast" with these beauties. :wink:

I could get a better photo with a light. Although even with a light, I couldnt see any cracks. Theres a lot of space in there hidden behind where the manifold bolts up. I was just curious if this was a common area for cracks?

None I've ever seen. You my friend have a bad head gasket. Pull the head. :!:

I had thought head gasket, but theres about an inch worth of fins seperating this area from the head gasket. I tried spraying the carb cleaner around the head gasket area without any effect.

Bowtoy70 said:

I could get a better photo with a light. Although even with a light, I couldnt see any cracks. Theres a lot of space in there hidden behind where the manifold bolts up. I was just curious if this was a common area for cracks?

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It is not a common area for cracks, but anywhere can be a common area for a casting void. Chances are there is a pore in the casting and if you can find it you can fix it with a little JB weld or other high temp epoxy.

Take the manifolds off and look down the ports. Then spray some carb spray where you did before and see if you can see a wet spot in the port. If you find it just clean the area and put a little epoxy on your finger and push it into the void from inside the port. jim

grandpaul said:

swooshdave said:

Les, isn't that the casting mark?

Click to expand...

Yes, casting line.

Click to expand...

Yes, I thought it probably would turn out to be a shadow from the casting joint, but one had to ask, just in case.

comnoz said:

It is not a common area for cracks, but anywhere can be a common area for a casting void. Chances are there is a pore in the casting and if you can find it you can fix it with a little JB weld or other high temp epoxy.

Take the manifolds off and look down the ports. Then spray some carb spray where you did before and see if you can see a wet spot in the port. If you find it just clean the area and put a little epoxy on your finger and push it into the void from inside the port. jim

Click to expand...

Yep - that's exactly what I'd do - except that I'd spray some crack detection powder down the port first to help find the wet spot. If I didn't have the right stuff to hand, a little flour, talc, or other fine powder rubbed over the area would do the same thing.

You didn't say anything about what head it is. A RH4?
I have one that cracked right where you described on a RH 4 head

Here's an idea for you...

remove the carbs. Take a piece of clear plexiglass and cut it to the dimensions of the inslulating washer, but don't drill out the port hole. Instead, mount a air tool nipple in the bore area. Bolt it up in place of the carb. (one side at a time) pressurize the port to 10-20lbs (with the intake valve closed) Spray soapy water at the outside of the casting to see if it bubbles outward under pressure to find your leak...

Obviously, this is a pain in the ass to do, but from your responses here you seem to be tracking the problem down. I know how tedious this crap is because I just had a cracked manifold myself which had all the same symptoms you have. Most auto repair places don't go to this length to find and fix this kind of thing. Instead, the head is replaced and they give you the bill. If it turns out to be something else, then you just bought a new head you didn't need... and the search will go on...

If you do the above procedure and find a crack or porosity, you'll be on your way to a fix, rather than just start throwing parts at it... Throwing parts at a problem does also work much of the time without having to find the exact flaw in the replaced part... but as an OCD person I like to find the cause of the problem because it helps me see the bigger picture of how things work which pays me back somewhere down the line with greater intuition...

It is a combat head, serial # 206xxx. Not sure if that makes it the head you are talking about.

we used to put chainsaws together with Pliobond. It is petrol resistant and bloody hard to remove. You have obvious cleaned the head where the leak is with plenty of carb cleaner or something. Get a 1/2 paint brush , full it with Pliobond wen the head is hot and jam it In there. The hole has to be going sideways into one or other of the inlet trackts.
iT S NOT GOING TO HURT IT AND YOU WILL GET THE PLEASURE OF RIDING STRAIGHT AWAY FOR VERY LITTLE COST.

Dereck

Pulled the carbs again. Sprayed carb cleaner down into the little nook, and looked for wet spots inside the intake tract. Couldnt see any obvious wet spots. I did however find a small pool of oil on top of one of the intake valves. It seems that I have a bad valve stem seal, so I guess Im committed to a rebuild now. If I pull the head, can a shop do a pressure test of some sort to check for cracks/porous spots? Thanks

Many years back I drove the bike past a metal recycling yard on Eastern Ave. S. , with the gates open and glimpsed what looked like a small pile of Norton heads in the bigger pile of metals. No , couldn't be. Came back around and yes it was. 10 or 12 of them. Had to leave but not too later learned of the porous Norton heads situation from rider buds and was grateful mine wasn't one of them.