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Best way to deal with these valve guides?
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sgellis
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PostPosted: Thu Jan 23, 2020 7:23 pm    Post subject: Best way to deal with these valve guides? Reply with quote

I picked up an old head with no cracks to have rebuilt. Knocked out the guides and found old repairs.

One exahaust valve was machined out to 14 mm. Also had the boss replaced. Was a bit surprised when it jumped up when the guide moved down past it.

Other exhaust valve is sleeved.

So thinking have the sleeve removed and just oversize the exhaust valve guides and reuse the fake boss. Is this the best way or oversize them all?

This for a 1600 single port with doghouse in a split bus. It won't see high RPM.

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Ohio Tom
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PostPosted: Fri Jan 24, 2020 8:31 am    Post subject: Re: Best way to deal with these valve guides? Reply with quote

Those heads look pretty bad..
Why not replace them?

Aluminum heads loose hardness over time. They get soft and then nothing stays for very long. Guides fall out. Seats fall out. Threads strip out.

To remove the old guids, drill them out to almost the OD.
Don't drill all the way thru. Leave a shoulder at the bottom of the drill.
Then drop a drift in there and hammer it out.

You can buy +.002" and +.004" guides from CB and other places.
Yes, you can re-use that sleeve.

but, as stated before, you are going to alot of work to save some old heads.

Will it be worth it?
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lelef
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PostPosted: Fri Jan 24, 2020 9:17 am    Post subject: Re: Best way to deal with these valve guides? Reply with quote

machined boss are used in 2 springs mods so the head should work without it
the best way is to make a valve guide in one piece with the boss , it's not an expensive work ,today you find everything ready made , years ago was usual to make valve guides with a lathe for a rebuilt or a tuned engine.
It's also true that a couple of new STD NON original complete heads are quite cheap and there are also a lot of options an prices for better and bigger valves.
Some more HP are always welcome
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Clatter
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PostPosted: Fri Jan 24, 2020 10:01 am    Post subject: Re: Best way to deal with these valve guides? Reply with quote

That guide boss thing is called a 'crutch' in some circles, and in the old days was seen now and again.

It is, unfortunately, a sign that this head is getting too old to be worth keeping.

I know single-port heads are getting to be rare(er) on the ground these days,
but,
if you want to be driving for some miles for a length of time,
Especially pushing a bus,
I'd be looking for a better core to rebuild.

Like was said,
once a head gets to this state,
the heat-treat of the metal comes into question.
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FreeBug
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PostPosted: Fri Jan 24, 2020 10:33 am    Post subject: Re: Best way to deal with these valve guides? Reply with quote

Ohio Tom wrote:
Those heads look pretty bad..
Why not replace them?

Aluminum heads loose hardness over time. They get soft and then nothing stays for very long. Guides fall out. Seats fall out. Threads strip out.

To remove the old guids, drill them out to almost the OD.
Don't drill all the way thru. Leave a shoulder at the bottom of the drill.
Then drop a drift in there and hammer it out.

You can buy +.002" and +.004" guides from CB and other places.
Yes, you can re-use that sleeve.

but, as stated before, you are going to alot of work to save some old heads.

Will it be worth it?


That's funny. I am not in any way calling into question your statement, just trying to learn something: heads DO get softer: the cylinder tops can sink in, and guides and seats CAN come loose...but at the same time, the alloy seems to become more brittle, too (so harder?), and starts cracking. Badly heated heads can be cracked ALL over, I saw some old formula V heads you could read a newspaper through.

So I guess the heads get annealed, but also get heat cycled?

just wondering...

Heads: change the heads if you want reliability, or don't if you're adventurous... Laughing
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raygreenwood
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PostPosted: Fri Jan 24, 2020 11:24 am    Post subject: Re: Best way to deal with these valve guides? Reply with quote

FreeBug wrote:
Ohio Tom wrote:
Those heads look pretty bad..
Why not replace them?

Aluminum heads loose hardness over time. They get soft and then nothing stays for very long. Guides fall out. Seats fall out. Threads strip out.

To remove the old guids, drill them out to almost the OD.
Don't drill all the way thru. Leave a shoulder at the bottom of the drill.
Then drop a drift in there and hammer it out.

You can buy +.002" and +.004" guides from CB and other places.
Yes, you can re-use that sleeve.

but, as stated before, you are going to alot of work to save some old heads.

Will it be worth it?


That's funny. I am not in any way calling into question your statement, just trying to learn something: heads DO get softer: the cylinder tops can sink in, and guides and seats CAN come loose...but at the same time, the alloy seems to become more brittle, too (so harder?), and starts cracking. Badly heated heads can be cracked ALL over, I saw some old formula V heads you could read a newspaper through.

So I guess the heads get annealed, but also get heat cycled?

just wondering...

Heads: change the heads if you want reliability, or don't if you're adventurous... Laughing


All metals....but especially aluminum and magnesium "work harden" as they expand and contract millions of times. Magnesium gets more brittle and is prone to cracking.
Aluminum...loses its elasticity. Bluntly put...after a while...through stress relief and metal fatigue.... it quits coming back to its exact cold size.

Thats when seats and guides start to fall out.

However...this can be fixed....but not that many shops do it except high end and racing shops.....and you can buy completely new castings for less money.

The aluminum heads can have their elasticity/temper restored through proper annealing. It entails removing all ferrous metal...studs, bolts, valve seats etc....and putting the head in an oven at a specific temperature and cooling in a controlled manner. It can be restored just like new....but when it comes out of the oven....virtually every single precision surface will have some level of change. Cylinder seating areas, valve seat pockets and in some cases even valve cover rails...will need to be re-machined.

Ray
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FreeBug
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PostPosted: Fri Jan 24, 2020 11:58 am    Post subject: Re: Best way to deal with these valve guides? Reply with quote

Thanks, Ray.
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sgellis
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PostPosted: Fri Jan 24, 2020 12:45 pm    Post subject: Re: Best way to deal with these valve guides? Reply with quote

FreeBug wrote:

Heads: change the heads if you want reliability, or don't if you're adventurous... Laughing


Haha. been adventurous now hoping for a bit more reliability Smile

Traveling through Maine in September I had to pull the engine to remove an exhaust valve in someone's a gravel driveway. Left out the pushrods and have put another 1200 miles running on three. Engine was needing a rebuild anyway.

The old head was to replace the one that lost the valve but I believe the seat could be replaced. No real damage that I could see. Got it turned off quick and it was low RPM at the time.

I will pull my engine in the next week or so and strip the heads, give them a good inspection and go from there. I have lots of duel ports but really want to keep this stock and its a bus so SP works well.

I will do a little research on those Mexican SP heads.

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mark tucker
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PostPosted: Fri Jan 24, 2020 1:12 pm    Post subject: Re: Best way to deal with these valve guides? Reply with quote

not worth wasting$ on.....
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modok
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PostPosted: Fri Jan 24, 2020 7:40 pm    Post subject: Re: Best way to deal with these valve guides? Reply with quote

Ten years ago I had a trouble finding a good PAIR of OE 311 heads for my engine.

Ended up with one head that was extra soft, and the other was extra hard.
Could tell from how they machined as well as how they sounded.
Oversized a few guides, installed larger seats, ext, ect.

Working just fine. Them being hard or soft does mean something....but not much. Probably just has to do with what happened to the heads in teh recent past, but not about what will happen in the future.

WASTE of time?
hmmm, well, I rather DOUBT any of these chinese heads would be able to go the same distance.

There is a point when you should call it quits, but, based on what is said and pictured you aren't there yet.
It is just fine to use "prosthetic" guide bosses on the exhaust guides.
Guides should have .001"-.002" press fit, lube with anti-sieze to install. Not rocket science. If it doesn't work you did it wrong.
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