Ryan Underwood wrote:
> jim beam > writes:
>
>
>>doing the valve & replacing the head doesn't "improve" the compression,
>>merely restores it to the cylinder that had lost it.
>
>
> Yeah, but presumably the rings have worn too. So bringing the cylinder back to
> spec may cause an issue there.

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.

>
>
>>detroit mythology. honda heads will happily stay on a block for 2, 3, 4
>>or more hundred thousand miles.
>
>
> What I meant was that OHC/aluminum heads seem to invite regasketing/warpage
> with mild overheat scenarios. Not as resilient as traditional heads.

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

> Though
> aluminum blocks are probably a bigger culprit in this area.

not if they're designed right.

>
>
>>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.
>
>
> 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.
>
>
>>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!!!
>
>
> 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.

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.

>
>
>>>So the idea is, either buy a new or rebuilt short block from a professional
>>>rebuilder with a warranty, or leave the rings alone?
>
>
>>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.
>
>
> I asked the question for future reference.

no problem. ask as many times as you need.

>
>
>>replace the valve, clean up the head & the block, put the head back on &
>>drive the car until you have another problem with it.
>
>
> That was the plan. Except now I'm not sure whether to get an exchange head or
> to have this one rebuilt

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.

>, given what you've mentioned above.
>
> Thanks.
>