A10 SR valve guides change

[eugenius]

Hi all, I open a new subject about an old topic to have some insights, A10 alloy head valves guide change. I have removed the inlet bronze guides because of an excessive lateral play even when testing with new valves. So far I have left the exhaust ones because they seem ok. The first question is, is it correct to leave 2 guides while changing the other two? And as far as the type of valves, colsibro guides are deemed superior by someone but maybe better replace with something similar to the old ones ? Another problem is the size. I have found very difficult to measure the guides seats size by the caliper, my range of measurements are from 12.90mm to 13.20mm but surprisingly the size of the removed guides were 14.50mm? There must be something wrong in my measure... Please help!     

[chaterlea25]

Hi eugenius,
The guides are nominally 9/16ths of 1 inch
0.5625in. = 14.288 mm
The interference fit would then be .002 in.
0.05mm bigger than above.
Were the old guides tight on the head?

If you cannot get a good measurement of the guide bores in the head, ask an engineering shop.
If all else fails buy the biggest oversize guides and have them machined to the correct size

John

[muskrat]

G'day Eugen.
You need to measure with a micrometer good for 0.0001", verniers are not accurate enough.
Did you push them out cold or heat the head (150-200C)?
Cheers

[eugenius]

G'day John and Muskrat, thanks for replying! I heated the head up to 200°C in the oven to remove the inlet guides by a custom made brass instrument and hammer. They were well tight but  I eventually pulled out them quite easily. I will try to get a more appropriate measure by a specialist because I don't have such a precise instrument. The old bronze guides size is 14.50mm (0.570inch), which seems oversized already?

Eugenio 

[RichardL]

As for doing all at once, I don’t believe it’s absolutely necessary, however, there is this to consider. When replacing guides the valves seats need to be reground to assure alignment. That will most like be done by the engineering shop, so, it is practical to do them all at the same time.

Richard L.

[eugenius]

Thanks Richard! Indeed I'm not going to embark in valves guides replacement by myself and I will bring valves, new guides and head to a specialist shop to do all at once. 

Eugenio

[sean]

if your going to take the head to a shop  ....remove the other 2 guides and replace all 4 ....time is money , and you dont want to pull it down again  when the exh guides go
you dont need colisbro I tend to go over the top with some things bronze guides are fine and tolerances easier to adjust .

[eugenius]

G'day Sean and thanks for replying! I will follow your advice and will change the four valves guides. Following removal of the exhaust ones I will ask for precise measurement of the seats size to decide which oversized guides is better to take. Thanks a lot for the expert insights from you and the all forum

Eugenio