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Cylinder head Rebuild Overkill?


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I'm wondering, is it overkill to just replace everything when rebuilding a cylinder head?  Valves, rockers, rocker shafts, springs, rocker hardware, guides, keepers, etc.  Will I save any money at the machine shop if they don't have to spec everything and I bring in all new parts, or am I throwing good money down the drain? I have no idea of the mileage or working condition of my Tii engine and want a good solid build, but don't want to waste money.  I guess this all came about after.my last question about the timing chain sprocket condition and it got me thinking.  For example, if valves are "within spec" should that be considered good as new, or am I still sacrificing some performance and longevity?

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I generally replace rocker arms, eccentrics, both shafts, valve guides and seals.  everything else can be reused after inspected. head and valves get machined and reground.  Upon reassembly make sure everything is very clean and free from any debris left from machining.

 

Cheers,

Matt

 

 

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A lot of "what to replace" is gonna be dependent on the car's mileage, and how well it's been maintained previously.   With frequent oil changes and no stupidities (like over-revving) an engine with 200k + miles may be in better shape internally than one with 75 k that wasn't properly maintained.

 

Early cars had un-bushed rocker arms, which actually wore the steel shafts.  The rockers on my '69 were nice and tight when placed on the unused sections of the rocker shafts, but the shafts themselves were badly worn--after only 100k miles and obsessive maintenance.  If you have bushed arms, check 'em for tightness by placing 'em on an unused section of the shaft and see if they pass the wiggle test.  And make sure the steel pads aren't loose on the aluminum arms.   So long as the adjusters on the rocker arms don't have flat spots worn on 'em, they can probably be re-used.  They're hardened steel so don't wear very much; they're harder than the valve stem that they contact. 

 

I would definitely replace the guides so you can use the later style valve stem seals, and then mic the valve stems for wear, in addition to examining the seating area for pitting.  You can buy better-than-stock quality valves, so if your engine is high mileage, new valves are a good investment. 

 

mike

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4 hours ago, bergie33 said:

For example, if valves are "within spec" should that be considered good as new,

No, they are within manufacturers "serviceable" limits. Theres usually a range. A new valve or component probably has slightly tighter specs.

4 hours ago, bergie33 said:

or am I still sacrificing some performance and longevity?

Minimal if any performance loss, as to longevity.. A properly overhauled engine, properly operated and maintained should run reliably and produce rated power for at least 50,000 miles.

Thats a lot of miles in an 02.

 

There is an article by Jim Rowe and Jim Blanton you should read, its very useful, very informative.

Dont have a URL to it, somebody might. I do have a PDF of it I can send you if you wish, if so PM me.

 

Have recently had 2 M10 cylinder heads at the machine shop for "a valve job"

They disassembled, cleaned and pressure checked prior to valve work.

First one required all new exhaust guides (intakes were ok) 3 new valves and 2 seats.

Second one needed all new guides, 3 new valves and 1 seat, it also had to be skimmed a little. 

 

 

Edited by tech71
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7 minutes ago, tech71 said:

There is an article by Jim Rowe and Jim Blanton you should read, its very useful, very informative.

Dont have a URL to it, somebody might. I do have a PDF of it I can send you if you wish, if so PM me.

 

 

 

I googled and found the articles.  Thanks, they look like they have a ton of great info.

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From a sorta different vantage point, I generally look at things from a 'wear parts' perspective.  As in, valve guides and rockers DEFINITELY wear (always sliding and/or against harder parts), whereas keepers, valves, and springs basically DON'T wear (hard and/or non-sliding), and rocker shafts and seats kinda fall in the middle (rotational/soft, but non-sliding).  So basically I'd order new guides and rockers going into a head job, and would be prepared to measure and order shafts if needed, and I'd still measure but be surprised if I needed to get new valves/springs/etc.  @tech71's post above would catch me off guard regarding the valves to be honest, but maybe that's just been something I'm off-base on then?

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1 hour ago, AustrianVespaGuy said:

@tech71's post above would catch me off guard regarding the valves to be honest, but maybe that's just been something I'm off-base on then?

Guess I didn't  mention why they required replacement , they were all bent so damaged, not worn out.

 

 

Edited by tech71
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Usually just the guides if they're loose, and the eccentrics if they aren't still round.

 

Everything else is reusable if it's in the middle or better of the spec.

 

Valves last an inordinately long time given how quickly a set of guides wears out...

it is worth dye checking the exhausts, as running really hot can crack them.

 

Rockers only with a new camshaft.  Then, always with a new camshaft.

 

t

not bothered

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On 8/31/2021 at 11:11 AM, Son of Marty said:

I'm with Matt, now days I might keep the shafts pending inspection as the price of them have tripled in the last few years.

Yes, I agree, however, most shafts I have seen are to far out of spec (mostly due to neglected oil or debris getting in there).  I have come across some decent ones and been able to polish up and reuse.

 

Thank you,

Matt

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Re: valves, and things I've seen on used valves from an M10:

 

- stems worn -> measure in various locations, I've seen 0.002" of taper (intakes wear more than exhaust)

- ground too many times, such that the seat area becomes too thin after grinding

- tiny cracks around the perimeter of the valve head

 

So, inspect and measure carefully.

 

Add: Some of the new stainless steel 'upgrade' valves found on the market have been of questionable quality (soft material, keeper grooves not ground correctly), hopefully they are better now. That's part of the reason I have quality stainless valves manufactured for use in my M10 engine builds. -KB

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