best head gasket for 90 EX 16V

Mostly, retorquing isn't needed these days, hasn't been for a couple decades now. For starters many head gaskets are the "no retorque" kind. Also, if you have "torque to yield" head bolts, as many engines do, to do a retorque means removing the head bolts and throwing them all out and putting new ones in.

For the aluminum block, you can use a wire brush but be careful with it - don't use a wire brush on a drill, use a hand brush and stop brushing when aluminum starts to appear under the old gasket material.. There are chemical products out there that are designed to clean off old gaskets you might try those. For a scraper, use a plastic ice scraper, not a metal one.

Don't sand, wire brush, or steel wool directly on the aluminum.

I would also recommend chasing the threads in the block with a tap. Some people just drill all of them out and replace them with HeliCoils.

Yes, if the head bolts are torque-to-yield you must replace all of them.

How many miles on this? Frankly, an engine that was owned by an owner who neglected oil changes is a poor candidate for new heads. Your better off just rebuilding the entire thing.

Ted

I was going to use brake cleaner and a plastic scraper as a start and save the aggressive stuff for later.

Ok, I've heard that there are two kinds of taps - real taps, and thread chasers, made out of different material, where thread chasers are made for cleaning up existing threads. Supposedly a thread chaser runs less risk of inadvertently doing something really bad to the threads. I was planning to get a thread chaser, but can you shed any light on this difference?

200k. Well, I should clarify. By neglected, I mean he usually let it get up to 5-10k between changes. This is neglect by my standards, but may be within reasonable tolerance. The reason I noticed it was because the valves were noisy when cold and I asked him about it.

Looks like a crank kit is about $300 and rings another $80. Plus the motor would have to be pulled to do the mains and the oil pump. If the compression is good and there is no play in the pistons, could the bottom end be that bad? What about just replacing the rod bearings from the bottom, and doing the rings through the top after getting rid of the ridge? I also don't know if the cylinder would need to be re-honed for the type of rings in this motor to seal up again, or if cleaning it would suffice.

Thanks for the reply.

oem.

as the head builder says, clean the surfaces only. any scratching can lead to leakage over time. new oem heads are mirror finished.

seals & tensioners are good.

that noise is not due to neglect. it's just a fact of life and to some extent, a function of the oil you're using. fortunately, a burnt valve is /no/ reflection on the wear status of the rest of the engine.

i'd be scrupulous about cleanliness for the block. new rings and seals are debatable at this mileage, but if it was good before and was not burning oil, personally i'd leave them. rebuilds usually fail in 1/3 or less time than the original build. analysis shows this is almost always due to microscopic abrasive contamination left on the cylinder wall after re-honing. if you can avoid doing that [and you /must/ hone if you re-ring] you could continue to get good service from this engine. caveat: "conventional wisdom" is strip, hone, ring, etc. but the fact remains that rebuilds don't last and for the reasons i've stated. i would not follow my own advice in a shop environment because i cannot be "negligent" for following conventional practice, but if it were my own car, and i /knew/ the block was good, sure i'd leave it as is.

Well, that's what I was hoping at least. The biggest concern of mine is that a new head, being perfectly sealed, will increase the load on the compression rings causing them to fail sooner, or at least increase blowby (fouling the oil more quickly and perhaps overloading the PCV system). But from what I've read, this seems to apply to older ring types and not to "moly" rings that new cars and especially Asian cars have been using, so this is nothing to worry about. (I'd love a correction here.) If so, that would definitely be a good thing, because most of these cars are also using OHC aluminum head designs which seem to invite eventual head rebuilds or gasket jobs for various reasons.

Aside from that issue, I'll just be on the lookout for detonation both from improved compression from the new valves, and from the unintended rise in compression that comes from the head being milled down.

So the idea is, either buy a new or rebuilt short block from a professional rebuilder with a warranty, or leave the rings alone?

How about bearings and seals? I seem to be under the impression that unless a bearing spun, they should be safe to replace (with a factory sized replacement) without a hot bath or crank job. Likewise seals, unless something catastrophic happened to the part they are sealing, just to use emery cloth or very fine sandpaper on any shaft burrs before installing the new seal.

Of course never having done any bottom end work, I'd prefer to have my head screwed on straight and do it right the first time or to not do it at all. That's an area where trial and error can get expensive and inconvenient, as one error can pile on more problems very quickly.

Thanks.

doing the valve & replacing the head doesn't "improve" the compression, merely restores it to the cylinder that had lost it.

to be honset, don't know what honda use these days or the dates. it's not really relevant to a valve job.

detroit mythology. honda heads will happily stay on a block for 2, 3, 4 or more hundred thousand miles.

1. you don't get increased compression from new valves.
2. you have no reason to skim the head just because a valve burnt.
3. if you /do/ skim the head, you need an oversize gasket.

again, you have no reason to skim the head. alloy blocks & heads often /do/ warp very slightly in use. but the important point most machine shops [trying to sell you their services] never care to mention, is that they warp in sympathy, so they still fit. unless you have a serious distortion, such as caused by a cooling failure, do not skim the head!!!

why do you want to touch the block? you burnt a valve. that does /not/ affect the block.

there's no point stripping the block, unless you plan to replace pistons, bearings, rings & seals, but again, i don't understand why you're contemplating that course of action. you're turning a $500 job into a $2500 job. maybe you want the experience, which is valid, but it's cheaper to pick up a $200 [or cheaper] motor from a junk yard and strip it down rather than be forced into much bigger $'s rebuilding this motor. and you'd be robbed of most of the experience anyway because in order to get any warranty, you'd have to let the shop do the rebuild.

replace the valve, clean up the head & the block, put the head back on & drive the car until you have another problem with it. /then/ figure out what to do. for a 90, replacing the engine with a used japanese motor is /way/ more cost effective [and probably reliable] than messing about with extensive rebuilds for the reasons i mentioned before.

Unless your engine is just dog tired and worn out this doesn't seem to be as big of a factor as it used to be. Were it mine I would get the head done and slap it all back together.

Unless you have a particular reason to suspect bearing problems in the bottom end I would leave it alone. If you start having oil pressure problems in the future you can always do the bearing then without having to redo the work you are doing on your heads now.

Take it from someone who doesn't know where to stop.... You have to keep the project to a managable size and avoid all the "might as wells" that pop up along the way. If a "might as well" is cheap and would cause you to have to redo a massive amount of work then do it otherwise leave it for another day.

Steve B.

Yeah, but presumably the rings have worn too. So bringing the cylinder back to spec may cause an issue there.

What I meant was that OHC/aluminum heads seem to invite regasketing/warpage with mild overheat scenarios. Not as resilient as traditional heads. Though aluminum blocks are probably a bigger culprit in this area.

Sorry, I didn't mention the new head is coming from an exchange rebuilder. So the choice whether or not to mill it down would be theirs, not mine.

Humm. Given this, is it a *bad* idea then to get an exchange head for an aluminum block? The new one wouldn't have the same "sympathy" warp that the block does.

[..]

I asked the question for future reference.

That was the plan. Except now I'm not sure whether to get an exchange head or to have this one rebuilt, given what you've mentioned above.

Thanks.

Solid advice, and the "might as wells" are exactly the problem I have when knowing where to stop. I'll try not to make a federal case of this one.

absolutely not. all that will happen is that your car will suddenly run well again. pistons running without load don't wear as fast as the ones with load, so if anything, this piston will be healthier than the rest. valves burn because they're not seating right or because they have a defect. it's got _nothing_ to do with what's going on 0.1" further south.

cast iron heads crack & warp just as effectively as aluminum.

not if they're designed right.

any "sympathy" warp is usually minimal. don't fret it - i just mentioned it in case you need ammo with the head shop - but i may have muddied the water because most places neither know nor care. but it's still best to use your old head if you can.

no problem. ask as many times as you need.

rebuild the old one. presumably it's just one valve. that makes the job $13 for the valve, $165 for the gasket kit, $70 for the chilton, $20 for the valve tool rental, and one half of a weekend. suddenly, you're back on the road. and pretty one-up on your buds too.

Thanks for your input. I may still get an exchange head for it just because of the mileage on it and the fact that I won't be the driver for much longer (being passed down to a teenager). Your comments give me a lot more confidence that this will be a successful job in the end.

200k is really not serious mileage for a honda.

Is it realistic to expect no other valvetrain problems given that at least one has already gone? Or say it's a broken spring instead of a burnt valve. The others wouldn't be far behind?

Maybe I've got the "Detroit" perspective going here again...

sure. unless they're badly adjusted or you have a problem like a broken spark plug insulator getting lodged under it, valves very rarely burn.

broken honda spring? they're as common as chicken lips. you need to be careful with a spring - any mechanical damage such as dropping it can leave small marks on the surface of the wire which act as fatigue initiators, but properly installed? no, honda don't break.