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as for the spare head.

going to look at drilling and tapping for 14mm x 1.25 spark plugs. have bigger range of plugs I can use and then the helicoil doesn't matter. I believe I already have this tap in my sets. of course all I have is a 14x1.5. just need to drill to 1/2" or 12.8mm. then tap.

head is not HC head. it has been decked already, but I can tell it has deeper bowls then the one on my car now. which means lower compression. may look at decking it further so compression is raised, especially with today's pump gas.

once I get the old head off i'll beable to tell the bowl size difference and get a machine shop to match deck height since I know the valves clear on the old head.

I know a lot of folks had their 10mm heads drilled and tapped for 14mm spark plugs "in the day", but I question if you really want to do it. First of all, 10mm plugs of proper heat range for your engine are available over the counter. Secondly, the threaded portion of the head with 10mm plugs is thinner than with 14mm, as the thread length of 10mm plugs is less. Thus when drilled and tapped for 14mnm you will have a portion of the 14mm plug threads protruding into the combustion chamber. These will get carboned up and make removal difficult, possibly stripping the threads in the process.

yes the threaded portion for 10mm is 1/4", but i can get 14mm in 3/8" reach. just 1/8" longer. and i can get them in platinum or whatever other more modern material I wish. maybe even Bosch platinum plus 4...never have to worry about gapping them again. have ran +4 in several cars and never had any issues. the newer ones will self clean much easier too as they will reach temps faster.

the only over the counter 10mm i can find is the autolite 3136. it is a hot plug. nothing wrong with that plug, just a basic copper core and i've had trouble with fouling, which people have argued over the smaller size contributing to that.

i'm not saying 10mm sucks or 14mm is better. my car has them now and i didn't think about drilling to 14mm on the old head. i just dont like that one hole is heli-coiled on this spare head and the cheapest most convenient solution is to drill and tap for 14mm. i can do that myself and it will be a good learning experience. if the head did not have a helicoil...i would leave it alone and just reuse my 10mm plugs.

regardless, there are pros/cons to either size, but i don't have any hate for 10mm. i'm just doing what i feel i need to do to get my car fixed.

Helicoils have a long and well earned reputation for being a quality remedy. If you put 100,000 miles on your car (unlikely) you will have to remove/replace the Helicoiloed plug only 10 times, not likely you will wear out the inner threads of it. If that unlikely event should happen you can easily replace the single Helicoil.

Henry, if you go forward with the 14mm spark plugs be sure to get the type that does not have a projected core. This type of plug may protrude too far into the combustion chamber and be struck by the exhaust valve. Maybe an extra gasket would prevent the plug end threads from being exposed to the chamber. Does DAF have a spare 282 head? I suspect your credit is good. Tough break. Take care. JWL

Decking a head to make use of today's gas is questionable. Original heads are about 6.5-7.0 CR, today's gas will withstand 10.0 or so. But you can't deck a 120 head to get 10.0, valves may hit and swirl pattern and flame propogation will be affected well before hitting those #'s causing pre-ignition/knocking. Are you building a hot rod or a driving classic??

i'm just batshit crazy Fred.....

The heads with the 10 mm plugs have much less meat in the thread area. If you drill and tap and re-spotface to accommodate 14 mm you will have very little thread engagement. I do not recommend it.

A crack on the top side of the head is inconsequential. Put a little stop leak in it and just drive it. A crack on the top of the head has nothing to do with the combustion chamber.

If you really want to use the other head, leave the helicoil alone. In aerospace practice EVERY tapped hole is helicoiled.
Do a simple truing up cut on the head and slap it on. Are you going to loose sleep at night wondering if you could have had 3 more horsepower?

its really not about power, its about having something I hope I wont have to worry about later and that cost me just about zilch. the last thing I wanted to do after busting my ass since September was to put a new head on the thing.

maybe some pictures will shed some light on the situation.

the crack is more then it seems. it goes from spark plug hole, across the top, and down the side. i'd be surprised if it did not spread, even with block sealer, which i'm not dumping into my coolant. heck i'd be surprised if the crack isn't on the bottom or at least spreads that way in the future. this head is junk.

on to the new head.

the temp gauge bulb was stuck in it, got that out and I hope the hole is okay, because I can't get the damn plug out the top of the head for the heater outlet. it might as well be welded in. screw it...its got a forever home.

as for the helicoil. part of it was sticking out the bottom as you can see by me lifting it with my finger. I put in a spark plug and it didn't even fit right and when I took it out the helicoil came right out. so much for that.

holes drilled to 1/2" and picking up tap today for 14x1.25. as for spotfacing....I don't have that tool...so either I get lucky or I take it to the machine shop and he is just nice and helps a brother out. cause paying hundreds in machine work right now is out of the question. He is a good guy though and I think he may help me out since I only got 400 miles out of the first one he did. if not....on she goes as is cause a 5 dollar tap and some cheap spark plugs wont break the bank. its also been decked in the past, its just dirty and has some surface rust on it. hit with the wire brush and slap it on.

the coolant is drained, but not before the POS aluminum allen head plug screwed up on me. so I had to drill it out and I got lucky and it spun out before I hit the threads. new steel plug in place. so at least now the crack isn't leaking and I can take my time.

I respect that you guys have so much experience and I don't disregard it. I'm just trying to do my best here. any of you guys are more then welcome to come on down and help me out in the garage, I could use the help. i'm tired..

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Henry,
I have five or six 282 heads on my spare parts. One is an HC. Of you need one later give me a call or PM.
Don