valve grinding

[conan383]

Hello new to this site, but right to the point-Built an all roller gen 1 sbc stroker with 10.87 : 1 , tight quench, 288/294 HR cam , 2000 ish year topline 200cc heads. Its a screamer! BUT took it apart to check out oiling issue . The sump had come off he pump, bracket broke. But anyhow the valve guide clearance was not acceptable so I had new guides dropped in. I dont know if he machinist was sleepy or what but one intake valve was sank into head more than the others. It was definitely not like that before. Its quite noticable at the tips and found it to be more than .060 deeper than the rest.Now he new he screwed up and put a bronze colored shim in it BUT put it on the wrong one , anyone that would have just put back on motor as is wouldnt have known, but since I dont trust anyone and its good measure to lap valves again I discoved A.- one intake not lapped and not sealing, B.- sunken intake valve C. that he tried to cover it up but put the shim on the next valve. So now the valve actually is shimmed .094, all most .100. I even told him to not touch the valve seats, It wasnt ran long enough to warrent a new grind , Ijust could have lapped em. I initually new they were a little loose but have ran other old school stock motors with more clearance so I went with it , it sucked oil past them even with good seals. So my questions are what are my options. Is .060 not enough to bother with and just go with crap job or will it affect the valve overlap being how intake is way lower than exhaust and cause it to flow more out exhaust? How bout bigger valve to bring it up out of seat? New seat inserts?

[ssmmith]

I would think any time you replace the guides you would have to grind the valve seats. There is no excuse for the other problems though.
Have a great day and good luck.
Steve

[rebelrouser]

sounds like when they installed the guides they got off center with the seat a little bit, and when they ground the valve seats they had to cut too deep to form a seat. If you take it apart if should be evident by looking at the bottom of the seat where the 60 degree cut is, it will be wider on one side than the other. After cutting and installing new guides you sometimes have a little seat run out, but it should not be so bad that you have to sink the valve to get it to seal.

[HDBD]

Now it needs a new guide in straight and a new seat.

[PRH]

It’s easy to second guess what the machine shop may or may not have done without seeing what they had to work with.

The original guide could have been badly worn, and pounded the seat in...... or off to one side, etc.

I’d want to have a conversation with the machine shop to find out exactly how the head ended up like it is.

Imo, If the seat was really so bad it required sinking the valve .060, then a replacement seat should have been installed.
After having that conversation with the customer of course.

And yes, obviously anytime the guides are replaced, the seats need to be touched up.

[mag2555]

To have to have a need to sink the valve .060" to get a good seat contact width back during what is normally a clean up valve job, that would mean that the new guide got shoved in at least .006" off from where the original guide was in, but that all being said, yes your in for a new seat now and a guide, both done by a better shop then who did that work!

Hopefully your chosen new shop can very closely match the valve job applied to the other 7 valves.

[hoodeng]

In some production cylinder heads the true of the valve assy is dictated by the final manufacturing step. That is, the seat bore and guide bore are machined in a one jig step, after the seats are installed the seat angles and guide bore are then finished true to each other. These production step stages have evolved and streamlined over the years, early shouldered guides obviously were installed from the spring side, then the head is re jigged and finished from the chamber side, later production had the shoulder less guides installed from the chamber side in the same jig the seat were installed in then cut true to each other,, at least one less re jigging operation in production, possibly more.

This is where the reconditioning problems occur. The resultant original finished seats and guide bores are true to each other, and not necessarily true to the original head casting seat bore and guide boring process. If we change either the guide or seat by themselves these will now possibly not be true to each other.

As years have gone by doing the same make engine you can see the tightening of production tolerances and processes over time, seventies heads that could have wildly all over the place alignment, and assemblies that reqd individual hand fitting and production QC steps, had steps reduced by changing production sequences.

One engine that came out in 84 and ran to 99 was a good case in point of a unit that benefited from continuous production assessment, the engine design wise didn't change much at all, a lot of areas were interchangeable first issue to last,,, but,, the quality and accuracy of the latter unit was far superior to the first issue.

Cheers.

[PRH]

The head in question is an aftermarket head from about 20 years ago.

My guess is, it had the seats cut as the last step, after the guides were already finished.

Sorta like this video from Dart in 2015:
https://m.youtube.com/watch?v=8S5arecvkYE

Assuming the head came with replaceable guides.......If the factory guide was severely worn, and the seat badly deformed as a result, it would have been a challenge to re-line the guide with any kind of accuracy to the original c/l, and replacement of the guide would have been the best option IMO.
Press out the old one, press in the new one.

In any case, I think most will agree that ending up with the valve sitting .060 lower in the chamber after the “repair”....... is a less than desirable result.

We’ll never know at this point, but it would have been interesting to see what was brought to the machine shop....... along with the various steps that led it to where it is now.

[conan383]

Thanks to all for the reply, and I'll let ya all know how the discussion with machine shop went

[1980RS]

I had that happen with a set of BBC heads and one guide was broken. The guy put in liners and got them all in spec but I told him "do not do the valve job" as I do that myself don't trust anyone anymore. After all the years of sheety valve jobs when I get done with my junk I know they seat. Every set of heads I buy new or used I take them apart and touch the seats and valves. I am happy with my results.

[hoodeng]

Another point i should mention is when replacing guides. It is not uncommon to see replacement guides with an id some number of thousandths undersized to the finished diameter, what we need to see is guides at close to on-size that require only final hone [some use dedicated carbide reamers] of hour glassing + clearance to complete machining. The reason? the more material you have to remove the more error in alignment can occur.
In seventies heads we found at the installation of new guides from a reputable manufacturer that were concentric and parallel, that after installation valves were miles off concentric to seats, this could only have been an error introduced at the manufacturing level.

And yes, there are places that will plunge cut a seat till anything that was good is now in the swarfe bed,,, and not one stem protrusion checked.. reminds me of the 'Norwegian Blue' Parrot in Monty Python.

Cheers.

[jcisworthy]

The head in question is an aftermarket head from about 20 years ago.

My guess is, it had the seats cut as the last step, after the guides were already finished.

Sorta like this video from Dart in 2015:
https://m.youtube.com/watch?v=8S5arecvkYE


I never used that machine but If the head does not float to a level when floating to a center, those seats are not concentric. It is very rare that two guides produce the same guide stick out. It almost neve happens.

If you install a head in a level fixture level and roll through the seats finding center only you will have a mess

[PRH]

If you install a head in a level fixture level and roll through the seats finding center only you will have a mess

The spindle in that machine is mounted on a air floated sphere, so it’s not only aligning the pilot to the guide in the x/y axis.......it’s aligned on all axis.

[jcisworthy]

Ok thanks. I wasn't sure if it was like a VGS and the operator was just floating on center and cutting seats.

[ProPower engines]

Ok thanks. I wasn't sure if it was like a VGS and the operator was just floating on center and cutting seats.

That is an issue that some guys never learn.
You must index to the center of the guide in both directions. Some guys take a new head and just level off a single guide and cut away which is wrong.
Pilot fit and tooling wear also play a part in a bad VJ.
The other issue is those old heads were not as hard on the intake seats as you would believe. But combine that with a shitty VJ and lots of spring pressures you may have pulled the valve into the bowl area and not really seen the difference when torn down till you clean them and start machining.
And if they were heads from the corporate buy out between Top-line and RHS they were not that great of heads quality wise.
We used lots of them and when top-line's days were over RHS just boxed up everything top-line had and marketed it.
We seen our share of defective heads back then. Even had some BBC heads with the exhaust manifold bolt pattern drilled backwards so the manifolds would be mounted upside down

The castings flow very well for out of the box heads but do yourself a favor and put all new intake seats in both heads that way you will not wear out the valve seats again.
the exhausts have 7000 series durabond seats installed at the factory so they will live a long time