Changing stem seals / adding valve springs with the heads on

[ofb383]

Hey guys, who's done the method of pressurising the cylinder with air to hold the valves up whilst adding the inner springs after break in or just to do valve stem seals with the heads still on ?
Is this quite straight forward, any do's / don'ts or pointers please ?

Thanks.

 

[65sporty]

It is pretty straight forward, plug any holes in the head with rags so nothing can fall down into the engine. You may have to give the retainer a slight tap with a hammer before compressing the spring to get the keepers out.

 

[rkrochen]

Yes it is fairly straightforward. We used to do it all the time as the seals only last for a certain length of time. You require a hose that can be threaded into the spark plug hole one from a compression gauge can be modified for this purpose. You need a pretty good compressor as there will be some air loss and it needs to keep up. You will also need a way to compress the spring, you can purchase a valve spring compressor for this. we made them out of old rocker shafts and modified rocker with a handle on it worked very well.
Apply air pressure then tighten up the spring compressor. You may need to tap the top of the valve retainer to get them to release. Remove and replace the seal and or spring and reinstall. After I always tapped the top just to insure the retainers were fully
seated. For the first time it may take 3 or 4 hrs.
Hopefully that helps.

 

[ofb383]

Well, I ordered a Air attachment from rockauto with a few parts I need and was thinking of this tool for the job?

 

[rkrochen]

That’s exactly what you need. good luck.

 

[Love Shack]

I’ve done that with the heads on a couple times. I think in the factory shop manual on this. Use caution. I always oil the new seals before I put them on. As stated above, be sure the locks/keepers are correctly seated before moving on to the next one. Good luck.

 

[swisherred]

When i did mine I didnt use air...I just used a skinny screwdriver...I put it in the plug hole and allowed it to hang...it provided enough upward pressure on the valve to hold it in place while i changed the seals and springs. I did not add pressure to it so it wouldnt damage the threads in the hole.

 

[68PK21 440.6bbl]

You may have to give the retainer a slight tap with a hammer before compressing the spring to get the keepers out.

+1

 

[swisherred]

and make sure you put the same retainers back on the same valves...I think mine were different...intake vs exhaust. 2 slots vs 3 slots.

 

[Trace 300 Hurst]

As an alternative to air pressure, feed a foot or two of clothesline (rope) into the plug hole (with some hanging out, of course) and run the piston up BY HAND until it snugs that line up against the bottom of the valves. Works perfectly, and you don't have to fear some sudden air loss and a vanished valve. Doh!

Obviously, you don't do this method stupidly and forget about the rope and crank the engine over, but if you're doing engine work at this level, you shouldn't be doing anything stupidly.

 

[65sporty]

As an alternative to air pressure, feed a foot or two of clothesline (rope) into the plug hole (with some hanging out, of course) and run the piston up BY HAND until it snugs that line up against the bottom of the valves. Works perfectly, and you don't have to fear some sudden air loss and a vanished valve. Doh!

Obviously, you don't do this method stupidly and forget about the rope and crank the engine over, but if you're doing engine work at this level, you shouldn't be doing anything stupidly.

I have never tried this trick, but I have always had the tool to use air. I read about this trick in Hot Rod or Car Craft years ago and it sounded good to me.

 

[70bigblockdodge]

As an alternative to air pressure, feed a foot or two of clothesline (rope) into the plug hole (with some hanging out, of course) and run the piston up BY HAND until it snugs that line up against the bottom of the valves. Works perfectly, and you don't have to fear some sudden air loss and a vanished valve. Doh!

Obviously, you don't do this method stupidly and forget about the rope and crank the engine over, but if you're doing engine work at this level, you shouldn't be doing anything stupidly.

I have had this one backfire on me. The valvehead cut the rope, stubborn locks. Did not know which one because it only cut about a inch and a half off. Of course it was a cylinder on the second head when we chose poorly on which head/cylinder to pull first. Nowadays I would just go to Harbor freight and buy a optical camera but this was in the early 80s.

 

[Trace 300 Hurst]

I have had this one backfire on me. The valvehead cut the rope,

Yes, good point. That can certainly happen. I guess I should have mentioned that you feed the rope in when the piston is about 1.5 inches from its TDC, so you know both valves are closed during that compression stroke for that particular cylinder.

 

[rkrochen]

I have literally done at least a hundred or more of these. Never would I recommend pushing or putting something down the cylinder when you have a perfectly good acceptable procedure already. I have never had any issues dropping valves. Everyone to their own though.

 

[ofb383]

I have literally done at least a hundred or more of these. Never would I recommend pushing or putting something down the cylinder when you have a perfectly good acceptable procedure already. I have never had any issues dropping valves. Everyone to their own though.

Do you opt for the air pressure method to keep the valves up ? If so what press do you use / recommend ?

Same question to the others that opt for the air method ?

 

[rkrochen]

Do you opt for the air pressure method to keep the valves up ? If so what press do you use / recommend ?

Same question to the others that opt for the air method ?

Yes I do. Most compressors run between 125 and 150. Somewhere in that range is good. When you tap the spring to release the keepers a small burst of air may escape but it is only momentary. You will also loose some air past the rings so you need a decent compressor. It doesn’t have to be big though.