Valve Guide Wear

[SprintMWU773V]

Looking at the repair manual I see the indicated limit for valve guide wear is just over 5mm when giving the valve a wiggle. This seems like a huge amount to me. I've definitely got some play in at least two of my guides but nothing like 5mm. Was therefore thinking time to replace the guides but on that basis it would be unnecessary.

[tony g]

Its another typo in the manual. 0.020" thou is 0.5mm Not 5mm

Tony

[MIG Wielder]

Yes, that's quite right. Section 12-13 para 12 in the Sprint manual shows how to measure this 20 thou as well. When Kyle & I were working on his 1850 head my local machine shop used a new "cold process" for doing valve guides. The original workshop manual method involves heating the head, removing the valve guides and replacing then with the special tool. The head is then machined to remove any distortion induced by the heat process.
What is done these days is that the old valve guides are reamed out, special inserts are put in and these are then reamed internally to suit the valve stems. It looks like these are made of phosphor bronze or similar from looking at them. The valve seats are then re-cut and only need a light grind in to get a perfect seal.
Tony.

[Richard the old one]

I have recently found an interesting problem on one of my 1500 engines. The car has only done just over 30,000 miles but when I was checking the valve clearances I noticed that one of the exhaust valve collars was turning black. On further investigation I found that this the associated valve guide had a considerable amount of wear and I believe that exhaust gas was traveling up the valve guide and heating up the top of the valve. All the other valve guides did not suffer from any wear. I removed the rocker shaft and there were no signs of oil starvation in that area but I have replaced the rocker shaft as a precaution.

I had a spare head so I had it refurbished which included fitting hardened exhaust valve seats and new valve guides as the ones fitted in this head were worn. The head came from an engine that had done a lot of miles.

I decided to fit an external rocker oil feed to ensure that the rocker shaft would get plenty of oil. Previously I had removed the external oil feed from another engine because there is a question mark over the use of this modification.

Finally I decided to see how easy it was to replace the worn valve guide as I did not have anything to loose. The old guide tapped out quite easily and with care I was able to tap in the new guide using a brass bar and hammer so that I did not damage the guide. The valve seat had not suffered much wear so I now have a serviceable spare head.

I believe this problem has been noted before but I have not found any person who can explain the cause other than that the original guide must have been defective. Can anyone help?