The potential pitfalls of 2nd hand heads

[Chancer]

I'm thinking of getting hold of a 2nd 4L HO head and doing a bit of porting and lapping in my copious free time. The donor vehicle has only done 47k, but had piston knock - what do the panel think: is this a lemon or will it be OK? If I can get it for the right price, I'd entertain some limited head work to rectify any damage, but what should I be looking out for, and what work should I be ready to have done to it?

 

[MudDawg]

Take the perspective head to a good automotive machine shop...have it disassembled, cleaned, magnafluxed and checked for warpage and valve guide/valvestem wear...if it is ok....have at it. Otherwise you could spend considerable effort only to find out the hard way that there is a problem. Only the most severe types of damage are visible to the eye.

 

[5-90]

As long as the compression on the engine is fine, more thanhalf of your worries aren't.

Piston slap is not only just a block issue, but a known issue with the 4.0 and doesn't seem to be that much of a cause for concern. If the price is right, I'd go for it.

Before you do any work, tho, you may want to invest in a "dye check" kit - what you get is a few small spray cans with some cleaner, some penetrant dye, and some developer that reacts with the dye. Follow the instructions, and the kit is used to check for surface cracks.

Check around the valve seats (mainly) with checks of the head deck for insurance.

The key questions I'd ask on a used head, if the owner is available:

"Has the engine been severely overheated?" (iron heads are more tolerant of heat than aluminum, but can still be cracked by overheating.)

"Have you ever had the head off?" if yes...

"Did you let it sit overnight before you pulled it?"
"Did you follow service literature when you pulled it?"

Those are the first that come to mind. The 4.0 head is a rather heavy iron casting and fairly resilient, so you probably don't have any worries -doesn't hurt to check, tho.

5-90

 

[bzdel2441]

See I am in the same boat here. I want an exta head to work in in my spare time but then again I dont want to get a crap head and spend a week working on it.

How much would you be looking at for "have it disassembled, cleaned, magnafluxed and checked for warpage and valve guide/valvestem wear" I mean you can get a reman head for less than $200.

Also alot of 4.0 at the junk yard dont even run so should I stay clear from thouse all together or could i still get a good head?

Thanks
Chris

 

[Dr. Dyno]

You might still get a good head from a non-running 4.0 in a junkyard but you'll definitely need to check it for warpage and have it magnafluxed for cracks. If the engine that it came from has oil that looks emulsified (with water in it), the head could be cracked or warped. Clean oil is a good sign.

 

[75SV1]

I P-n-P a 4.0L head a few months back. Engine still not done, but calculus is. Anyways, I think it was $25-30 to have it cleaned and magnafluxed. I don't think it was more than $50. I did see someone selling a 4.0L head on E-Bay saying they had $90 in the head being cleaned and magnafluxed. I remember thinking they got hosed. I would get the head cleaned anyways if you are going to port and polish it. You will still get some cast iron grime from handling it, but it should be a lot easier to to the job.
Tom

 

[Chancer]

Wow, thanks everyone. An awful lot to think about. The head in question is out of an XJ that's being broken, and it would be shipped to me, so I'd have to ask the questions (and buy it) without actually seeing it, so I guess it would be a bit of a lottery as to how good it is. However, from what you all say, it sounds that the heads are pretty tough and that as long as I can check it over for a reasonable price, then it would probably be worth it - is that right?

Excuse my ignorance, but what does a dye check do, and can you do the check with the thing separated from the rest of the engine? Also, would I be best just taking the thing to a reputable machine shop for checking over before anything else?

 

[5-90]

A "dye check" is essentially a "quick and dirty" Magnaflux - only instead of using megnetic fields and indicator particles, you are using a penetrant dye and a developer. Advantage: the kit fits in your pocket. Disadvantage: It only chatches surface defects. For our purposes, however, that's not a problem.

http://www.midwayautosupply.com/detailedproductdescription.asp?171

This link will give you an example - but I don't know how you'd go about getting such a kit across the puddle. You may want to start with jobber shops, machinery shops, and places like that to find this thing - it can be quite handy sometimes (I also check yokes when I change U-joints, for instance) and usually retails over here for about $30.

Good luck!

Oh - and I'd defenitely have the head checked out at a machine shop before I did any work on it.

5-90

 

[Dr. Dyno]

Wow, thanks everyone. An awful lot to think about. The head in question is out of an XJ that's being broken, and it would be shipped to me, so I'd have to ask the questions (and buy it) without actually seeing it, so I guess it would be a bit of a lottery as to how good it is.

It would definitely be a lottery since you won't actually see it unless you get it. The fact that it's coming from an engine that's only done 47k miles yet it had piston knock does raise a red flag. If the engine was severely overheated, the head could be warped or cracked and you won't find out until it's too late. The '99+ heads with casting no. 0331 are more prone to crack than earlier heads so you really need to watch out with these.

 

[Chancer]

Thanks for all of that. I've found out that Magnaflux is over here, indeed they even have a list of distributors on their website - very handy.

As for asking about the condition of the head, it's a 93, so is slightly tougher than the later ones, and I've asked the relevant questions about ownership/ mileage verification/ overheating and oil and water consumption, so I guess I just have to wait now and trust to honesty! I'll keep you posted.

Thanks again.

 

[MudDawg]

Just in case this thread is still being reviewed....I agree that the fee to check the head will average around 50 bucks...more, up to around 100 bucks in a shop where they actually MEASURE everything....as for the valves and guides, if they are not within spec the engine will use oil and the nice 3 angle valve job will be down the tubes quickly. The only long term repair is to replace the guides and worn valves...do not let anyone "knurl" the worn guides to "repair" the problem...that is a "used car lot" repair....It will not hold up more than a couple of thousand miles..

 

[Chancer]

Thanks - yes, I'm still reviewing the thread. I've found a good shop near to me who'll check the head for £35, which ain't bad. They also do a lot of restoration work, including vintage and veteran cars (Fraser Nash 1927 racers and stuff - cool...), so I think they should see me right.