What's new
CK5
Register an account today to become a member! Once signed in, you'll be able to participate on this site by adding your own topics and posts, as well as connect with other members.

Using Compressed Air for Valve Seal Replacement...question

B

Big6ft6

1/2 ton status
Joined
Apr 26, 2010
Posts
251
Reaction score
6
Location
Madison, WI
Will putting compressed air in the spark plug hole cause the engine to rotate?

OK guys, I am going to hook my compressor up to the spark plug hole in my tbi 350 to help diagnose low compression. You want to keep both valves closed during the process. I have the engine rotated to the correct spot to both valves on this cylinder are closed...but suddenly I was worried that if I applied the air it might rotate the engine.

Anyone done this for valve seal replacement to tell me how it worked out? Putting the tranny in park doesn't lock the engine (flexplate) in place does it?
 
Rotate the engine so both valves are closed so the cylinder will hold air pressure. You only really need like 20 pounds of air pressure to keep the valves up maybe even not that much I can't remember what I had mine set to the last time I did mine. With that little pressure it won't be enough to rotate the motor.
 
Like stump said LOW PSI. If no regulator is available, I've used a pair of needle nose vice grips to lower the pressure (start tight and loosen slowly). Too much will rotate the engine.
 
Put the piston at BDC and you'll have no worries about rotating the engine.
 
Phil513 said:
I'm gonna use the nylon rope method. I think.
Click to expand...

I have used that method,I do not trust air pressure to hold the valves closed--too many times I had the engine suddenly turn over,even with it at perfect TDC and had a vise grip clamped on one of the v-belts,it spun the other way and made almost a full turn!--and was lucky I had wrapped a rubber band around the valve stem to prevent it from dropping out of sight into the cylinder,right after I took off the spring..on an older high mile motor,the valves may not seat perfectly enough for air pressure to work too..(if that is the case,the right thing to do would be pull the head(s) off and do a valve job..

The rope method does take longer,but not as long as having to pull the head off to retrieve a dropped valve..

By the way,I have used a air hose nipple with 1/4" NPT threads to apply air in a cylinder to check for leak down,or hold valves,without the need for an adapter--the tapered pipe threads are a pretty close fit to the 14mm plug hole threads--finger tight with a wrap of teflon tape works for me..I have also used the hose off my compression tester as an adapter,it has an air chuck coupling on one end,and spark plug threads on the other (both 14mm and 18mm)...
 
Diesel4me....that was my original idea to use my compression tester adapter, I had it all set up but no air would go through???...then I looked and at the end of the adapter that threads into the spark plug hole and I could clearly see a one-way valve inside of it to only let air out of the cylinder and not in....I was really bummed I thought that was going to work perfect.
 
Its a schrader valve. like in a valve stem in a tire. If you have a removal tool it will unthread.:waytogo:
 
You must log in or register to reply here.

Latest Posts

Top Bottom