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Valve Guides - Cast Iron?


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#1 Haynes

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Posted 18 April 2019 - 09:16 AM

For as standard 998 head rebuild is there any reason not to use cast iron guides?

 

Someone mentioned getting some Mag bronze guides, as these seem to be used on all the performance heads.   But minispares are out of stock so will probably go for standard iron ones.



#2 panky

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Posted 18 April 2019 - 10:03 AM

No problem what so ever, get the MPI valve seals while you're at it, better quality.


Edited by panky, 18 April 2019 - 10:05 AM.


#3 Spider

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Posted 18 April 2019 - 11:09 AM

Cast Iron Guides are very good.

 

The Mag/Bronze ones are also good, but MUCH less forgiving than the CI types.



#4 DeadSquare

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Posted 18 April 2019 - 11:36 AM

No problem what so ever, get the MPI valve seals while you're at it, better quality.

 

I like plenty of oil down the valve guides.

 

I call it "Upper Cylinder Lubricant"

 

It is especially beneficial if you are running on Castrol 'R'.



#5 unburntfuelinthemorning

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Posted 18 April 2019 - 12:46 PM

 

The Mag/Bronze ones are also good, but MUCH less forgiving than the CI types.

In what way are they less forgiving?



#6 Cooperman

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Posted 18 April 2019 - 06:44 PM

If the running clearance is too small the valves can seize in the guides.
I always use CI guides with MPI stem seals.

#7 Spider

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Posted 18 April 2019 - 06:44 PM

 

 

The Mag/Bronze ones are also good, but MUCH less forgiving than the CI types.

In what way are they less forgiving?

 

 

If the head over-heats, they usually grab the valves and then float in the head.



#8 unburntfuelinthemorning

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Posted 18 April 2019 - 09:12 PM

 

 

 

The Mag/Bronze ones are also good, but MUCH less forgiving than the CI types.

In what way are they less forgiving?

 

 

If the head over-heats, they usually grab the valves and then float in the head.

 

Ooo, that's not good.  I have a Calver head with manganese/bronze guides.  Better be extra careful not to overheat it!



#9 Cooperman

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Posted 18 April 2019 - 09:43 PM

I fitted the then-new manganese-bronze guides in a 970 Cooper 'S' which had a 286 cam. The valves seemed to run smoothly in the guides when it was assembled, but when it got hot one valve stuck in its guide. I had to take the head off, open out the guide a bit, but then it happened to another valve, so it was not just a 'happenstance' the first time. I stripped the guides out, fitted cast iron ones, reamed them out accurately and it never gave any more problems.



#10 unburntfuelinthemorning

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Posted 18 April 2019 - 09:49 PM

Fair enough.  The maganese/bronze ones can't be all bad though or they just wouldn't be used.






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