I frequently read suggestions about warped heads on OHC engines. I'd like to hear comments of others on this matter. My reason bring this up is, I have seen camshafts broken in half because the cam bearing bores are no longer in line
horizontally. With aluminum heads I know they can be bolted to a surface
plate and heated several times in an electric oven to pull them back. Cast iron
heads such as the Ranger engine would require surfacing and boreing and sleeving the cam bearing bores. Comments please.

 

Just my $.02's, if it's that bad, it will cost more to correct the issue than buy a replacement head...

--Mike

 

I was driving a GF's Datsun 510 and had the camshaft break. It was wierd but I was able to figure out that the cam was broken just past the first cylinder. It would run (rather badly) and I was able to drive it home on that one cylinder. Aluminum head.

 

Once a head has warped for any reason the camshaft bore must be re-machined as well as the head surfaced all around.

 

My late aunt had a Datsun b-210, the old boxy one. Her "friend" mechanic sold her a valve job or head gasket replacement. His 'mechanic' did the valves, and then, when re-assembling the cam to the head, broke the camshaft which had been working fine before disassembly. He told her 'these things break all the time, you need a new one'. I was 400 miles from home or I would have hauled it out of his shop and fixed it myself, so she said OK, and it was finally repaired.
The reason the cam broke? The 'mechanic' tightened the cam bearing/hold downs completely starting at one end of the head, instead of torquing them each down a little bit at a time, or did the same when releasing the tension on the valve springs. There is no other way that camshaft broke, and she, about 75 at the time, was being taken for a ride by her 'friend' that had maintained her cars for over 10 years. Made me sick to see this 'religious' person do that, especially to someone who knew so little about cars. Oh, I was so mad I could have spit tacks.
Regarding warpage, I think that it would be a good idea to check the line bore on the cam bearings after an OHC head has overheated. It can be done with a long straightedge. You'd see the 'bow' one way or another if you laid a good straightedge in the bearing bore, top and bottom.
tom

 

Some of those AL heads don't even have bearings. The cam rides directly in the aluminum. I had an IZUZU like that. I scrapped it after the head blew for the third time.

 

Yup. Many Aluminium heads don't have separate bearings. Cologne 2000 and Lima 2.3 do have separate bearings. The Mazda designed DOHC in the latest Rangers.. Can't state for fact if they have replaceable bearings.
Things have changed while I have been looking the other way. Used to was that you could buy an el-cheapo car, put some labor into it, and make a few bucks. Kind of work your way up from budget transportation to something you'd drive cross-country. Now it seems that cars are made of parts that are un-repairable, made of high-priced material or highly complex parts, such that you can not afford to repair them. Back in the mid '80s, you could get a 2-3 year old Ford Escort with a cracked (aluminum) cylinder head, and it was not economical to repair. The cylinder head cost about half of what the car was worth, including something for labor. Many a low-mileage Escort was in the boneyard for want of a reasonable repair cost. I have put rings in stove bolt chevy engines, and turned the rod bearings top to bottom and put it back together. It burned as much oil as gas until that 12 hour 'rebuild'. At a cost of less than $50. Can't do anything near that today. People probably throw away Taurus that have a leaky heater core, or Explorers with the bad heat control mechanism because of the repair expense for minimal parts. The same thing holds true for all of our electronics. Fix? Ha. Off topic, but I'd bet it is going to be hard to find a machine shop in a few years, except for specialty (read:hot rod,race, etc) work. People will not spend anything to repair, and we don't seem to be training many people. I think when some look down their nose at people with a skill and knowledge(read:technicians) that they can't even come close to understanding, something is wrong. Spit and bailing wire just won't do it any more.
tom

 

Yeah, I know. Off topic. And too long. tom

 

Off topic suits me fine.

Used to was that you could buy an el-cheapo car, put some labor into it, and make a few bucks. Kind of work your way up from budget transportation to something you'd drive cross-country.

That describes most of the cars I've ever owned. Drive 'em for years and they run better than when I first get them.

 

I understand completely.

 

Man do I agree Tom. Thats why I'm going backwards with a '77 f150 and propane. Will work on it and drive it and let someone else buy the disposibles. I guess that's ok if you know thats what your doing but I'm done with that game.

 

Some of the old Ford tractors did not have cam bearings either, and that's in cast iron.