Hot Rod Forum banner
1 - 7 of 7 Posts

·
Registered
Joined
·
238 Posts
Discussion Starter · #1 ·
I was looking at valve stem seals and find there are many. And I am not real confident on this subject.
I took a look at the Dart web site, it says my heads are cut for umbrella seals. So is there any reason to do otherwise?

The guides have a 9/16" OD (.5625")with a flattened conical and well centered top.

One of the reasons I ask is that the valves and pistons were pretty carboned up. Engine has 5 years of summer use, mostly 2700 to 3300 rpm cruising. With some idle putts and a very few blasts to wide open, and near WOT.
But, I also need to confess this has been my learning experience engine. So it has been run rich plenty of the time which I imagine contributes to carbon deposits. AND, I am certain that I hacked the first umbrella seals as I put them over the valves.

One the one hand I'd like to not carb up my valves and piston tops, on the other I do not want to starve my guides of lubrication.

I should be better at keeping the products of combustion down now. I got myself an AFR setup and vacuum gauge last year and it made a lot of difference.

So, umbrella seals?
 

·
Registered
Joined
·
15,316 Posts
Umbrella seals work till they don’t, that of course can be said of positive seals as well.

Umbrella seals really aren’t a seal in the sense that they don’t wipe oil from the stem they really are a deflector redirecting oil away from the stem and guide not actively preventing oil entry as a seal would. Generally if you’re running a spring more complicated than an outer with a flat damper there isn’t space for these. They do work loose on the stem which lets them move from redirecting oil from the stem to actively pumping it down the stem. Then they eventually harden and break apart.

With the upper guide diameter at .5625, you would have to machine the OD to either .531 or .500 to fit the available seal stem ID clearance and even smaller at .494 if you run nested springs. Tools are catalog available if you choose this route. You need a pilot, cutter, and decent half inch drill motor, drill motor cost aside you’re looking at about 100 bucks for tooling. Hard seals can actually run the stem and guide too dry. This is more a problem on the exhaust side than intake as exhaust stems are hotter and see pressure at the guide base where intakes are cooler and see a vacuum at the guide base.

Bogie
 

·
Registered
Joined
·
1,159 Posts
Rubber umbrella seals slide up and down with the valve. They do a good job to keep oil from running down worn valve guides. Kind of a band-aid really.

I suspect your Dart heads are machined to take "positive" seals which you tap down onto the valve guide boss. They are typically made of Viton and are available in a few diameters.

Umbrella seals:
Automotive tire Sports equipment Rim Circle Auto part


"Positive" seals:
Wheel Tire Automotive tire Azure Rim
 
1 - 7 of 7 Posts
Top