C3 backfire.
Race Director
Joined: Jul 2015
Posts: 13,082
Likes: 3,398
From: SW Florida.
The rope trick. You feed in a bunch of rope and then you turn the front balancer with a wrench to jam the Piston up against the Rope wedging the valves in place. feeding the rope in by itself doesn't do any good until you do that.
Le Mans Master
Joined: Aug 2017
Posts: 8,336
Likes: 2,809
From: Cool Northern Michigan
If you have exhaust manifolds, you could go with the compressed air sparkplug hose adaptor. If you have headers, it will be a S.O.B. to try to get that hose adaptor in there.
With all the sparkplugs out, work on one cyl at a time. The rockers will help you figure out if you are at TDC on that cyl. The piston has to be at TDC or the compressed air will rotate the engine slightly.
Before installing the spring compresser, take a rubber mallet and bang on the valve stem. That will prepare the splitlocks / retainer for removal. When you order springs, just worry about diameter first, then find a low pressure stock type spring. Order good stem seals ($20-25) instead of junk umbrella or "O" rings.
Its not a horrible job. Number one fear is dropping a valve in the cyl. You can control that with strategy. Take your time, you will get it.
With all the sparkplugs out, work on one cyl at a time. The rockers will help you figure out if you are at TDC on that cyl. The piston has to be at TDC or the compressed air will rotate the engine slightly.
Before installing the spring compresser, take a rubber mallet and bang on the valve stem. That will prepare the splitlocks / retainer for removal. When you order springs, just worry about diameter first, then find a low pressure stock type spring. Order good stem seals ($20-25) instead of junk umbrella or "O" rings.
Its not a horrible job. Number one fear is dropping a valve in the cyl. You can control that with strategy. Take your time, you will get it.
Last edited by HeadsU.P.; Dec 28, 2017 at 06:48 PM.
Instructor
Joined: Aug 2017
Posts: 180
Likes: 24
From: Jacksonville Florida
I don't, but I'm sure I can find one, or build one. I've never been this far into a Chevy, I come from the Mopar side of the world. Could I replace my bad spring and be on my way? Or should I do all 16? Or pull head and make sure I still have something resembling a valve seat? Heads are bone stock L82's.
Le Mans Master
Joined: Oct 2006
Posts: 7,123
Likes: 433
From: Gladstone MO
C3 of Year Finalist (appearance mods) 2019
If you're going to replace all 16 springs, I'd get on the phone and call someone like Comp Cams- TELL them you're replacing the stock springs and would like to get better quality stock pressure springs. Bet they can fix you up. Comp Cams is only a suggestion, any of the good parts people could point you in the right direction- Straub, vortecpro, you pick.
If you get infected with the dreaded :whileimatititis" disease, you could swap to tool steel 10* retainers and new locks too, along with a new set of PC valve stem seals.
If you get infected with the dreaded :whileimatititis" disease, you could swap to tool steel 10* retainers and new locks too, along with a new set of PC valve stem seals.
Drifting
Joined: Aug 2013
Posts: 1,263
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From: perth Aus w.a
2020 Corvette of the Year Finalist (stock)
C3 of Year Winner (stock) 2019
I had two broken springs in my L68 . I used the air to hold up the valves and made sure each piston was at the top while doing the springs .My machinist found some Isky springs that worked for me .Once I got all 16 springs in ,set the valve lash and was good to go. 
Is my vette stock?? HAHA
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From: Im not allowed to tell you
2020 C3 of the Year Finalist - Modified
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Race Director
Joined: Jul 2015
Posts: 13,082
Likes: 3,398
From: SW Florida.
the rope works better. gives you something to bang the keepers loose against without being a hard piston top. and the valve cant drop in. do #1 then just follow the firing order around 1 at a time.
Racer
Joined: Nov 2017
Posts: 289
Likes: 32
I can't imagine trying to stuff the end of a rope through a spark plug hole. I have been using about 20 psi of air pressure all my life to hold the valves closed and with that cylinder on TDC of its compression stroke. About 40 years ago I made air fittings from old spark plugs; a 14 mm short reach, a 14 mm long reach, and an 18 mm for the earlier Fords. I have an 18" length of hose attached to the fitting and screw it into the hole just like a compression tester then I couple my air chuck to it. I give the side of the spring retainer a gentle tap to break the keepers loose then compress the spring with a home made lever. It only takes about an hour to replace all 16 valve seals or springs by using 20 psi of air pressure.
Melting Slicks
Joined: Dec 2009
Posts: 3,195
Likes: 632
From: Thunder Bay
I can't imagine trying to stuff the end of a rope through a spark plug hole. I have been using about 20 psi of air pressure all my life to hold the valves closed and with that cylinder on TDC of its compression stroke. About 40 years ago I made air fittings from old spark plugs; a 14 mm short reach, a 14 mm long reach, and an 18 mm for the earlier Fords. I have an 18" length of hose attached to the fitting and screw it into the hole just like a compression tester then I couple my air chuck to it. I give the side of the spring retainer a gentle tap to break the keepers loose then compress the spring with a home made lever. It only takes about an hour to replace all 16 valve seals or springs by using 20 psi of air pressure.
I've been doing it with compressed air for about 40 years. (Although I use about 30 psi, and yes this is enough to force the piston down if its not at the bottom, and is probably more than you need.) Quick and easy. Isn't anyone worried about introducing dirt into the cylinder by stuffing rope in there?
Last edited by drwet; Dec 29, 2017 at 03:04 PM.
Thread Starter
Cruising
Joined: Dec 2017
Posts: 13
Likes: 0
Just got back into town and was able to do more than start up and idle.
Still pops through exhaust something terrible under acceleration. Seems to be when engine is under load. Idle is much better. Still only passenger side. Throttle response much better.
Vacuum is much better, but has a 2hg rapid fluctuation (down from the 10-12 hg rapid flux.)
Have strong 150 psi of compression on all 4 of that side.
My thoughts:
1. Could need to reset valve lash
2. mixture? Seems to run/idle okay, just pops through exhaust under load)
3. Timing (Set at 37@2800 total)
I could possibly upload a video to explain my problem more clearly.
Still pops through exhaust something terrible under acceleration. Seems to be when engine is under load. Idle is much better. Still only passenger side. Throttle response much better.
Vacuum is much better, but has a 2hg rapid fluctuation (down from the 10-12 hg rapid flux.)
Have strong 150 psi of compression on all 4 of that side.
My thoughts:
1. Could need to reset valve lash
2. mixture? Seems to run/idle okay, just pops through exhaust under load)
3. Timing (Set at 37@2800 total)
I could possibly upload a video to explain my problem more clearly.
Thread Starter
Cruising
Joined: Dec 2017
Posts: 13
Likes: 0
Had good compression, couldn't fathom a bent valve would yield me decent compression...
Plugs and plug wires are brand new.
Le Mans Master
Joined: Aug 2017
Posts: 8,336
Likes: 2,809
From: Cool Northern Michigan
Back to drawing board. Sharpen chaulk.
Maybe the valvelash is a little on the tight side on that one valve. Sometimes when setting the lash a lifter has bled off (slack). Then when you go to start it up, it builds up pressure in the lifter, slack or lash is removed. But now, does not allow the valve to close completly. Pop thru the EXH.
Maybe the valvelash is a little on the tight side on that one valve. Sometimes when setting the lash a lifter has bled off (slack). Then when you go to start it up, it builds up pressure in the lifter, slack or lash is removed. But now, does not allow the valve to close completly. Pop thru the EXH.