View Single Post
  #4  
Old July 17th 05, 03:54 PM
jim beam
external usenet poster
 
Posts: n/a
Default

Ryan Underwood wrote:
> jim beam > writes:
>
>
>>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.

>
>
> 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).


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

> 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.)


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

> 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.


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

>
> 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.


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!!!

>
>
>>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.

>
>
> 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.

>
> 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.


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.

>
> 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.
>


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.

Ads