bb water cooled exhaust valve guides

[Chris H.]

I was reading in the Restorer CD that these guides can sometimes leak coolant into the exhaust port. I noticed that one of my exhaust ports has a sort of "shiny" residue and was wondering if that could be remnants of coolant into the the exhaust port.

[Joe L.]

Re: bb water cooled exhaust valve guides

Chris-----

I do not understand how there could be a connection between valve guides and coolant leakage to the exhaust ports, or anywhere else, for that matter. On Chevrolet V-8 engines with cast iron cylinder heads, the valve guides are "integral" with the cylinder head. In other words, they are simply holes which are bored through cast bosses on the cylinder head. I suppose it's possible that cracks could develop within the guide area, but I've never heard of the exhaust valve guides being particularly subject to this.

[motorman]

Re: bb water cooled exhaust valve guides

not on BB chevys,the guide are pressed in and then drilled for the valve stem. that is why when you replace the guide it is sometimes off center of the valve seat. yes they do go through the water jacket. if you have a leak into the exhaust you will see rust around the guide.

[Joe L.]

Re: bb water cooled exhaust valve guides

motorman-----

Interesting. I guess I've never looked close enough to see that the guides are not an integral part of the cylinder head for big blocks as they are for small blocks. In any event, GM has never had a replacement valve guide available in SERVICE for big blocks.

[motorman]

Re: bb water cooled exhaust valve guides

the aftermarket does but as i stated before the guides in the head some times does not have the hole concentric with the OD and replacing the guide will cause you trouble. the best way is to bore out the orignal guide and sleeve it. if you have a leak around the guide i would try moroso block sealer.

[Joe L.]

Re: bb water cooled exhaust valve guides

motorman-----

Now I think that I understand most of the reason for my confusion on this subject. Whenever I've seen big block cast iron head valve guides replaced, I've always seen the procedure used which is the same as that used for small blocks (i.e.boring out the existing valve guide hole and installing inserts). Since, in most cases, cylinder heads with removable valve guides have the old guides pressed out and the new pressed in, I guess that I just assumed that the big block guides were the same as small block.

Based upon your information regarding the occasional lack of concentricity between the guide OD and the valve guide bore, I would strongly suspect that during manufacture these guides were pressed into the cylinder heads in the unbored condition, more like a "plug". Then, the valve guides were bored so that the bore was perfectly concentric with the valve seat, which would be critical. If an entire valve guide were to be replaced, the concentricity of the valve guide bore to the valve seat could be lost. In fact, if the heads were manufactured as I suspect, the only way that one could be assured the necessary concentricity would be to overbore the existing valve guides and install inserts (as you described) or install unbored guides and bore them so that they are concentric with the valve seat.

I learn something new every day.

[Chris H.]

Re: bb water cooled exhaust valve guides

Joe, if you have the restorer CD do a search on TRW on up will pop the article. It's an internal TRW paper that addresses the coolant leaking bb exhaust valve guide. I tried to do a cut and paste from the cd but it didn't work.

[motorman]

Re: bb water cooled exhaust valve guides

joe, i consider a day wasted if i do not learn something new! motorman