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1800 Cylinder head cracks?

Posted by hanker 
Hank R
Denver, CO, USA   usa

I've got a buyer for a used 74-1/2 thru 80 cyl head. I need to clean it up and get it magnafluxed. WHERE ARE THE MOST COMMON PLACES THESE CRACK. I want to make sure the guy is getting a good head.

Thanks in advance for any input.
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twigworker Avatar
Jack Austin
Blowing Rock, NC, USA   usa

Most common? Try between #2 spark plug boss and the nearest head stud or across to the edge of the head surface.

Also look closely at all of the combustion chambers, particularly for radial cracks emanating for the plug boss hole and moving toward either of the valve seats.

Jack



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ron neal Avatar
Coastal, South Carolina, USA   usa

I just sent head number 5 to the machine shop looking for one with no cracks. Good luck. I am going into the boat anchor business next.

Ron
dickmoritz Avatar
Dick Moritz
Philly 'burbs, PA, USA   usa

Also in the area of the number 3 spark plug hole...

Dick



Errabundi Saepe, Semper Certi
(Often wrong, but always certain)
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twigworker Avatar
Jack Austin
Blowing Rock, NC, USA   usa

Oh no Ron !

Keep collecting and sell them to the Indian gent who comes around picking up scrap to make manhole covers!

Jack



---------------------------------------------------- Services to Interesting British Automobiles-- www.jackscars.net ----------------------------------------------------------------
-------------I like to think that I don't service automobiles so much as I provide entertainment, fulfill dreams and revive wonderful memories --------------

I am in the northwestern North Carolina mountains, right up against the Blue Ridge Parkway. Lawn chairs are in the shop and always time to talk. Drop in any time.

Member Services:
Over 40 years of caring and capable services to British cars and their owners. For help or advice please call 828-295-0224, email to jackscars@charter.net or go to www.jackscars.net.
curtis7420 Avatar
Curtis Wright
Univerisity City, MO, USA   usa

here's an article with pics...

http://www.flowspeed.com/cracked.htm

should be all you need winking smiley
Basil Adams Avatar
About 12 miles from Sears Point, CA, USA   usa

On the late heads, there's often cracks in the exhaust seats. Sometimes between the push rod tubes and up from a spark plug hole to a valve guide. Check everywhere. Best of luck. Basil



Basil C. Adams
1956 MGA Coupe (Show Car)
1957 MGA Roadster (Driver)
1958 MGA Coupe (Racecar)
1959 MGA Coupe (unrestored)
1960 MGA Coupe (unrestored)
1960 MGA Roadster (Driver)
MKIII Elva Courier (E1056)
1967 427 Cobra
1972 Alfa Romeo Montreal
A coupla late MGBs
1960 Austin Healy BN7
More Cars than Brains
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Rob Medynski
Canterbury, N.H., USA   usa

The head should be checked everywhere. I've found cracks on the outside around the plugs, between the chambers and around the seats. On the later heads, one of the two small water holes around each spark plug on the head surface are not drilled. I would line the head gasket up, center punch the holes and drill them out to improve the coolant flow. I've talked about advancing the cam before. 18V engines have 4 degree retarded cam timing. Advancing the cam, also lowers the combustion temp along with giving you torque and better mileage. Distributors used from the early 70s on, often have retarded ign timing for emissions. I would often change it to a early 25D with performance specs. Retarded distributor timing cooks the head. That is the main reason, it's hard to find a good later head and a long story made short, ended up manufacturing distributor vacuum advance units.
Rob
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Dave Headley
Cortez, 4 corners, Colorado, USA   usa

The very early 12H906 heads rarely crack externally, but I've seen several with combustion chamber cracks.confused smiley

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Hank R
Denver, CO, USA   usa

Thanks for all of the input. I'll clean the head, get it magnafluxed and cross my fingers.
Bustr01 Avatar
Steve H
Denver, CO, USA   usa
1978 MG MGB "Minnie Grace"

Hank,

I'd like to know what shop you select for the magnaflux. I have a used head I'd like to get checked, too. Thanks in advance.

Steve
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ron neal Avatar
Coastal, South Carolina, USA   usa

I finally got one good head which was a early smog head, 2 bad 18v late heads and 2 bad 18v big valve heads are all boat anchors or the next manhole cover.

If you think you have a stash of heads that may be good I would have them checked for cracks. Your stash may be boat anchors. My odds were 1 out of 5.

Ron
Hank R
Denver, CO, USA   usa

Well guys, my head had one small, not visible to the naked eye, 1/2" long crack in #2 and #3 exhaust seats. Maybe repairable by installing hard seats? Has anyone tried and succeded in that kind of repair? I no longer have the head advertised for sale, but just wondering. Another manhole cover perhaps?
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