cracked head - intake port; best fix?

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km-eek
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cracked head - intake port; best fix?

#1

Post by km-eek »

10 years ago when I had the heads redone on my '63, there was a crack in the intake port of the rear head which the shop welded up. Hardened steel valve seats were also installed. They have held well during 15-20k miles of riding, often at 70+ mph. Presently, the rear cylinder only fires intermittently until the engine warms up after about 2 miles, then it runs fine. After a long trip I see that the left exhaust pipe is brownish-yellow (normal richness) while the right pipe is black (rich- but typical for an old harley). Its not the plug (changed plug-same thing), its not the wire (changed wire-same thing), I tightened the manfold clamp (still the same).

Next is a manifold pressure test, which Mr. Cotten always stresses, but at this point I'm about 95% certain that old crack has opened up again, and closes once the engine warms up. My concern is that conventional welding or "brazing" with pot metal that melts at 700*F will further crack the head. JB weld, an epoxy, can be heated red-hot & still seems okay. Also, perhaps I can work some into the crack while the head's cold, while with welding or brazing the crack will close during the process, only to open again as the head cools. WHAT ARE YOUR THOUGHTS ON THIS MATTER? Panhead Ken
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Re: cracked head - intake port; best fix?

#2

Post by nmaineron »

You should take it to a good welder that knows his stuff with aluminum.
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Re: cracked head - intake port; best fix?

#3

Post by Hog54 »

Yeah sounds like a bad weld.
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Re: cracked head - intake port; best fix?

#4

Post by Diesel 68MC »

The head will need to be heated evenly before welding a industrial hot plate table works for this then the head will need to cool off slowly in a controlled temp. enviroment a oven works well for this. ive done this before on various things that needed this process. the wife didnt like parts in her oven but hell with her lol.
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Re: cracked head - intake port; best fix?

#5

Post by 58flh »

DEF. take the head to someone with exp. on panheads!---The hardened seats could have loosened-up to!--Never should hardenedseats be in stalled on panheads!--They were originaly cast in with the mold & nwere ZINC>!--The thing to do is reline the old zinc-seats with new ones of the same matieral! Then do a valvejob!-,Valves will have to be tipped for correct hight & this is the proper way for freshening-up panheads!--The cracks that you get from plug-hole to valve can be welded by somebody who has done this dozens of times!, I weld the plug-cracks!--But even though I know how to do all forms of welding THATS as far as I would push my limits on panheads!---There are some good threads in the knowledge-base on this!--Also (HEAD-HOG)-is the best for bringing our brittle heads back to life!--You can call & ask for DON!--Tell him your situation!-Also have pics. to e-mail him so he could see what the extent of the damage is!--BEST of LUCK!---RICHIE 8)
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Re: cracked head - intake port; best fix?

#6

Post by Cotten »

Ken!

You will need a #9 rubber stopper with a hole in it for testing the head without the manifold attached.

The worst possible scenario is if the crack intersects with a headbolt insert.
This usually occurs when the crack is caused by the installation of a hardened seat.

.....Cotten
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Re: cracked head - intake port; best fix?

#7

Post by 58down »

got a source for the zinc seats?Have several heads that need repair.Thanks, :?
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Re: cracked head - intake port; best fix?

#8

Post by UPSROD »

I believe the original seats are bronze not zink.
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Re: cracked head - intake port; best fix?

#9

Post by Cotten »

Somebody posted that Kibblewhite was making bronze seats,
and some OEM replacements still exist,... somewhere.

The risk is that the combustion chamber may already be relieved beyond those seats, and a raw, un-sized seat is needed.

I have un-sized K. O. Lee seats, but alas, they are tool steel.

....Cotten
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Re: cracked head - intake port; best fix?

#10

Post by 58down »

cotten,
Which seats would YOU run?
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Re: cracked head - intake port; best fix?

#11

Post by Cotten »

58down wrote:cotten,
Which seats would YOU run?
58down!

Someday I hope to get around to the set with hardened seats I installed myself,
but they seem to last forever on the shelf.

If I should ever need to get back into such things,
bronze would be choice number one, two, and three.

....Cotten
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Re: cracked head - intake port; best fix?

#12

Post by steve_wood »

Ken,

Headhog can install a bronze seat for you. Normally he uses his patented process to build up the bronze of the original seat, but he also has the material to manufacture and press into place a bronze seat.
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Re: cracked head - intake port; best fix?

#13

Post by km-eek »

Thanks for all your input. I went over to my neighbor, a marine mechanic, to do a bit more testing. I limped over on one cylinder hitting.

First, with the engine idling, we sprayed starting fluid on the O-ring seal area and on the head in the intake port area of the rear cylinder. If these areas were leaking we would expect to see the engine speed up as the rear cylinder gets fuel instead of air. It did not.

Next we checked compression. 60 psi rear, 140 front. A few squirts of oil in the rear cylinder would determine weather it is rings or valves. If its rings the pressure will come up with oil. If valves, likely not. 140 psi after oil in the rear cylinder. The cylinder has a piston/ring issue - possibly scoring from overheating.

The engine hit fine on both cylinders for about 1 minute after I started it again, then settled into missing after the oil squeezed out. I'll check for a cracked head when I take it apart.
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Re: cracked head - intake port; best fix?

#14

Post by Cotten »

km-eek wrote: .....First, with the engine idling, we sprayed starting fluid on the O-ring seal area and on the head in the intake port area of the rear cylinder. If these areas were leaking we would expect to see the engine speed up as the rear cylinder gets fuel instead of air. It did not......
km-eek!

You only proved that you do not have a big leak.
Bubbles tell all.

....Cotten
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Re: cracked head - intake port; best fix?

#15

Post by steve_wood »

And a small leak could be the reason the rear cylinder overheated to the point of damage.

Keep digging!
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