23 replies to this topic

[Minitransition]

Stripping and rebuilding an A+ automatic.

 

Took head off, removed valves and turned head over - heard a tinkle sound !

 

On cylinder 2 the exhaust valve seat had fallen out and cylinder 2 inlet valve was loose enough to remove with my finger !

 

Anyone else had this please ?

 

Can you buy oversized valve seats ?

 

How else to repair a perfectly good head?

 

On reflection a clue was that bores 1,3 and 4 were carboned up, cylinder 2 amazingly clean - probs been like this from new?? Inadequate seal and not firing properly.

 

Many thanks Andrew

[Pigeonto]

Get in touch with Keith Calver. I gather he has adjustable cutter set therefore he could make new inserts to  just over the size of yours which fell out and fit new ones properly

[Ethel]

I'd look closely for cracking, but you may not see any even though there is one. They're an interference fit, so I don't think anyone could say without measuring if you can get away with just having a new one pressed in.

 

Machine shop job I'm afraid, which may not be worth it if it's a stock head.

[matty...]

You can buy valve seats in finished form or unfinished, that will require cylindrical grinding to size.

Your best bet would be to take it somewhere that can machine and fit them, then you'll know they are fitted correctly. We always fit them by warming the head up and freezing the seat to -40 degree C, they should just fall in like this. The likely hood is they were fitted by pressing them in, which doesn't work as it resizes the hole as the seat is pressed in.

Have you checked that the head isn't cracked between the seats or anything, seems odd they have both fallen out.

Edited by matty..., 29 October 2015 - 09:24 PM.

[Spider]

You can buy valve seats in finished form or unfinished, that will require cylindrical grinding to size.

Your best bet would be to take it somewhere that can machine and fit them, then you'll know they are fitted correctly. We always fit them by warming the head up and freezing the seat to -40 degree C, they should just fall in like this. The likely hood is they were fitted by pressing them in, which doesn't work as it resizes the hole as the seat is pressed in.

Have you checked that the head isn't cracked between the seats or anything, seems odd they have both fallen out.

 

That's pretty much what I do with them when fitting them up, though most shops hammer them in (with a proper dolly) and that's the normal accepted practice with cast iron heads - that always makes my toes curl up!

 

I usually buy the seats ready to fit, but if it needs to be an odd ball size, I have a bar of the correct material (a type of Stainless) that I turn them up from.

 

The interference should be 0.003 - 0.004" per 1 inch of diameter of the cut out.

[ACDodd]

I did an experiment once, I drifted in a valve seat insert and then pulled it out to see the damage. There was none. The recess retained its fit diameter.

 

AC

[ACDodd]

Happy to take a look at your head, although we have to see what caused the seat to become loose. If crackes as already mentioned, no chance really of a reliable repair. However, it needs to be inspected to determine what can be achieved.

 

AC

[Guess-Works.com]

A picture would be helpful

[Minitransition]

Thanks, have inspected and no crack visible, it is a standard 998 head. Thanks for offers of look / fix, I have a nearby machine shop (Classic & Modern) and will pop it along to see what can be done. Why do exhaust valves have inserts anyway?

[Minitransition]

I probably mean why do both inlet and exhaust valves have inserts? Is it  exhaust that needs hard seat for unleaded ?

[Guess-Works.com]

the inlet should not have an insert, or at least would not normally have one. which is why I suggested a picture as I'm as intrigued as you are...

[Minitransition]

Please see attached - hope photos work !

 

One of both inserts having come out of cylinder 2.

 

One of cylinder 4 which hopefully shows inserts in inlet and exhaust !

 

Mystery !

 

 DSC_0084.JPG   50.49K   33 downloads  DSC_0086.JPG   39.34K   24 downloads

[Guess-Works.com]

Well it's certainly not factory, so probably been done, badly one might add, at a local machine shop.

 

IMO, you may as well ditch the head and get another...

[Spider]

Seats are usually only fitted to the Inlets if the original seat has eroded or gotten damaged to the point that it can't be re-dressed without the valve becoming too recessed. It's not too common to need them on Inlets, but like Guess Works, I gotta wonder why, on a head like this, it's hardly an economical repair and it appears that whoever did them previously didn't know what they were doing.

[ACDodd]

Woah there, factory 998 heads do have an insert for both inlet and exhaust valves.

Ac