xflow valve guides.

[techbod]

Winter refresh got to dealing with the head now.

 

All the valves (inlet and outlet) have side to side play in the guides - am I right in thinking that there should be none, even when cold, and the guides need replacing?

 

I know the guides run in the head, but local machine shop have given a reasonable quote on fitting inserts into the head.

[Roger King]

Firstly, there should be a small running clearance. If there is none, you will seize a valve. But it should certainly be minimal - without going into measurements, you should just have a perceivable amount of play if you hold the valve about 3/4" off its seat and try and wiggle it.

 

Some of the valve materials that Caterham have used in the past were good quality, but were unfortunately incompatible with the standard cast iron guides drilled directly into the cylinder head - this lead to rapid wear.

 

Assuming you have no need to change the guide design to accommodate better stem seals (or for any other reason), the simplest and cheapest way would be to fit a bronze liner in each guide. This requires specialist equipment and may be what your machine shop is proposing. I would strongly advise against just fitting replacement cast iron guides; a bronze running surface is compatible with just about any valve material and is also OK with unleaded.

 

Do make sure that they are equipped to cut seats properly though - this WILL need doing afterwards and when done well will allow the seats to lap-in in one go.

[Eugene]

Check for unleaded seats too 😳

[techbod]

Thanks for the replies - very much appreciated.

 

The movement is more than just perceivable - for want of a better description you can 'click' the valves from side to side quite noticeably. It may be the reason I'm getting oil collecting in the combustion bowl, most noticeably of piston #1. (Rings/bores being checked as well).

 

The machine shop is proposing using bronze guides and then re-cutting the seats. Judging by the large number of heads being dropped off and picked up this is something they do day in and day out. I'm probably being a touch disingenuous calling them a machine shop, they only do engine work and having asked them lots of dumb questions, their advice seemed to match, so fingers crossed and I've handed over the head to them to sort out.

 

cheers.