Which are better, the white plastic seals or the black rubber seals? The black ones are listed as being high temp and cost more, is the price difference worth it?
Chevy umbrella exhaust valve seals.
- Thread starter Clone TIE Pilot
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If the heads are off the car, then have the guides machined for positive valve seals. The umbrella seals are not very effective. Also, many an engine builder will advise that seals on the exhaust valve are not really needed because there isn't any vacuum in the exhaust chamber at the base of the valve stem (but I always put them on.)
Regarding your question, I'm not familiar with any umbrella style seals other than the black, soft type.
Are the heads on or off the car?
Regarding your question, I'm not familiar with any umbrella style seals other than the black, soft type.
Are the heads on or off the car?
I've only ever used the black rubber ones, never had any problems. I never put them on the exhaust valves and I've never had anything burn oil after doing so.
They do help, I replaced broken and melted ones on Olds 5A heads on a 350 block. It was like driving an old chevy, blue puff on start up, good thing it was in my 94 Z71. For Olds the black and white look like the same material. Between that and freeing up the piston rings, it cut oil consumption in half. It was mostly exhaust valves where the melting and damage occurred. The last two sets of #6 heads had the positive seals added. When I swapped from the well used set to a pair with fresh guides and seals, oil consumption went down a lot. It shows, worn guides are worn guides, seals being same. Would new positive seals on the well used pair help, maybe.
This is for my HO 305. In stock form they used positive seals on the intake valves and umbrella seals for the exhaust valves. However, I am not sure which type of umbrella seals to use as the part sellers list both types.
Good Day Clone Pilot & all; First we need to know if your guide bosses are machined for the positive style (PC) seals? If Not do Not use the PC style they will not work! Way back during my shop years the boss preferred to use both the umbrella & O-ring style on the bosses that were Not machined. And few heads were machined back then, so that was the norm. Assembly sequence, shim, umbrella seal, spring, retainer, O-ring seal & keepers. Other note if guide is worn the PC style will fail soon as it doesn't have a lot of flexibility. And of course the OE umbrella style tend to get crisp sooner on the exhaust valves, they're closer to the heat. The O-ring style embedded between the retainer & keeper tend to have a cooler working environment. Closer to the cool (OK hot, but cooler than exhaust valve boss) oil source. Take care, Ole' Bob.
Thanks varnah. I looked at my GM pdf repair manual for 86 MCs and Caprices, and it shows all 305s of that year use positive seals on the intake, and umbrella seals on the exhaust. I would assume that at least the intake bosses are machined if they use positive intake seals from the factory. These are smog motors and positive intake seals do lower emissions and reduce vacuum leaks for improved idle vacuum. Not sure if the exhaust bosses are also machined so I am just going to order the black umbrella seals that are marked high temp which are nearly double the money over the white plastic umbrella exhaust seals.
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