LS PM guides, stem clearance?

[turbo camino]

LS 243s, stock PM guides, Manley 11360 intake valves, reusing OE exhaust valves

Intake valve stems: .3130-.3131, this is about 6 tenths smaller than the OE intake valves that came out

Intake guides:
.3154
.3153
.3152
.3153
.3155
.3153
.3155
.3156

Yes .0026 is technically still within the factory production limit, but man. Sure does feel like a pile of slop. Are they really OK being run this loose?

[turbo camino]

Should I have used a more clickbaity title, something like "Singh grooves and minimum CSA"?

[turbo camino]

The issue here, I'm realizing, is that the Manley valves are undersize (and also inconsistently undersize from valve to valve). They list the spec as .3133", these measure from a low of .3130" to a high of .3132". Is this typical of Manley valves? This is the first time I've used them.

Each and every one of the original used valves with who-knows-how-many 100k's of miles on them measure exactly the same .3136".

[68corvette]

I have used 0.03mm on intake and 0.04mm at exhaust as clearances.
With stainless, chrome plated valves, I would prefer to use liners, or bronze guides to ensure that no galling is happening.
Chrome stem works well with "iron" guides as long as chrome is not worn.
When chrome wears, stainless will start seizing fast to the guides.

Also with bronze guides you could use slightly less clearance.

[PRH]

Wouldn’t the factory exhaust valves be stainless with plated stems?

[turbo camino]

Exhaust is stainless (or something non-magnetic so I assume some flavor of stainless) with chrome stems. OE intakes are also chrome stems. Manley replacement valves are also also chrome stems.

I can only find about one tenth wear anywhere on the stock valve stems, comparing against the plated but unworn section between retainer and seal location.

I can only find about 3 tenths wear in the guides, comparing the largest point at top/bottom and inline with the rocker against the least-worn area in the middle of the guide and 90* to the rocker. There is slightly more than 1 tenth out of round in the worn sections at top/bottom.

The guide geometry is more than acceptable for reassembly, I'm not thrilled by the variation in sizes but based on the wear it would seem that's just how they were made at the factory.

Why are the Manley valves undersize? They aren't a conversion valve, they shouldn't need new guides to fit the application.

[turbo camino]

I have built many SBC heads and replaced and sized many SBC guides, but I have never seen a situation where the replacement valves were undersize whether a stock replacement or aftermarket stainless. Also never seen 2 tenths variation in stem diameter in a single set of new valves. But then, I have only used 'cheap' stainless valves like PEP or equivalent, never the high-dollar name brand stuff like Manley. Maybe this is just what the extra money buys. If PEP made a valve for this application we wouldn't be having this discussion.

Just to restate: These Manley valves are 3 tenths smaller than their published spec for stem diameter, and 6 tenths smaller than the valves they are supposed to replace.

[engineguyBill]

Valve guide to valve stem clearance of .0024" to .0026" is fine. As long as the stem clearance is within factory specs, all is well. Tightening the clearances is not a good idea, especially if you are running positive valve stem seals. Too little clearance here will cause the valve stems to gall and/or seize.

[turbo camino]

I used to do this for real in a previous life, I would have called .002 as borderline but probably OK to reassemble for the pig farmer's truck, anything over that would have got new guides.

The factory specs are .001-.0026 production, and an unbelievable service limit of .0037. Obviously too tight is worse than too loose but at what point does valve sealing and/or seat damage/wear become a concern? If you were replacing guides and had an unlimited budget what numbers would you shoot for with a "8mm" stem and PM guides?

[Truckedup]

Seems like allot of clarance? I build vintage air cooed bike engines ,not car engines. Using modern single axis valve seat machining, clearances of 001 intakes and .just under. 002 on the exhausts. Bronze guides with seals on the intakes, 5/16 stems.

[houser45]

The .0027” clearance would be considered worn out. With new valves I would have the clearance honed to .001 intake .0015 exh. Put liners in them from k line

[PRH]

I see new assembled heads right ootb with .002 clearance all the time.

And depending on the application........ on the exhaust side....... that may not be enough.

I’m not saying what’s right or wrong for the OP’s application....... but it sounds like if he wants to tighten up the clearance the choices are:
Find valves with larger diameter stems, or put liners in and size them accordingly.

[PackardV8]

The .0027” clearance would be considered worn out. With new valves I would have the clearance honed to .001 intake .0015 exh. Put liners in them from k line

Today's oils and pump gas don't always play well with tight guides.
Rebuilders who do many engines every day and have to warranty them would never put together .001"/.0015". They've seen too many hung valves, sometimes even on startup.

Having said this, they're using inexpensive .015" oversize stem rebuilder valves in a reamed and honed guide. If one is using bronze liners and expensive valves, your opinions and experiences may vary.

[turbo camino]

I have ordered a set of cheap stock replacement SBI 02000's which claim a real honest-to-God stock replacement .3136 stem diameter. We'll see.

[Truckedup]

The .0027” clearance would be considered worn out. With new valves I would have the clearance honed to .001 intake .0015 exh. Put liners in them from k line

Today's oils and pump gas don't always play well with tight guides.
Rebuilders who do many engines every day and have to warranty them would never put together .001"/.0015". They've seen too many hung valves, sometimes even on startup.

Having said this, they're using inexpensive .015" oversize stem rebuilder valves in a reamed and honed guide. If one is using bronze liners and expensive valves, your opinions and experiences may vary.

I siezed a few valves on the bikes trying to tighten up valve to guide clearance. I was told unless the seat to guide bore was dead on concentric I couldn't do it even with nitrided stems in bronze guides.Now I use a shop wth a CNC Newen valve machine and tight clearances are no problem. There are a few guys who claim they can do an equal job with tradtional valve facing tools.
My stuff runs good but do the tight clearances make more noticably more power?