Valve seals
Thread Starter
Instructor
Joined: Jul 2003
Posts: 118
Likes: 0
From: Twin Lake Mi
Valve seals
I have a miss in the 350 engine of our 1970. A few issues have been taken care of but it still persists. I have one plug in particular that keeps fouling. I have been told I have bad valve seals. Is this something that I should have done by itself or should the complete heads be rebuilt? In the past I have heard that if the seals are bad, then the whole engine needs a rebuild. What would be a fair price to have justs the heads done? I'm not taking them off myself. I just don't have the time to do it. The speed-o-meter shows about 97,000 miles. The car received a "Top Flight " award with the previous owner in 1995. I am well aware that this in no way assures me the engine was also rebulit properly with the restoration. Last year the car ran smoothly. This year it really shows the miss when you down shift to make a corner & accelerate to shift back into 4th gear. It also used to run well in 4th gear at 25 or 30 mph. Now it does not. Thanks for the advice in advance. We're starting to feel like were driving a money pit.
Burning Brakes
Joined: Jun 2004
Posts: 872
Likes: 3
From: Cortlandt Manor New York
Needing valve seals does not mean you need a rebuild. If you get some smoke on start up that might mean you need valve seals. If they are not functioning oil will leak down into your cylinders after you trun off the car and burn off when you start it up.
It could foul your plugs and cause a miss but you really need someone who knows Corvettes to check the car out and find out what the cause is. It could be simple or it could be a major repair.
If you don't want to spend the money replace the spark plugs and check that you are getting spark to each plug. It could be as simple as a bad wire or plug that is causing it not to fire and foul.
It could foul your plugs and cause a miss but you really need someone who knows Corvettes to check the car out and find out what the cause is. It could be simple or it could be a major repair.
If you don't want to spend the money replace the spark plugs and check that you are getting spark to each plug. It could be as simple as a bad wire or plug that is causing it not to fire and foul.
Thread Starter
Instructor
Joined: Jul 2003
Posts: 118
Likes: 0
From: Twin Lake Mi
At this point in time, I have changed plugs three times. I originally did it last fall just because I figured they were old & needed replacing. The car ran fine before I did that. That is when the troubles started. It had AC R45s & I ordered from a catalog since there were some other items that I needed. The ones I received were R43. It seemed to run smooth at first but after 25 miles or so, I could sense a miss. I checked & found the plugs didn't match what I had originaly so I bought some more. I didn't notice the "s" so I bought R45. It still had the miss so I checked the old plugs again & noticed the "S". I now have the R45s plugs installed. I tried a tight 35 thousandths gap and now I'm going to try a loose 35. I also have a new cap & rotor & new plug wires. I just feel with my luck it will turn out to be more.
Pro
Joined: Dec 2004
Posts: 570
Likes: 0
From: glace bay nova scotia
a simple compression test will tell if it's seals or if you have a real problem.If compression is good,add a set of wires and cap,also points if you are still running them.
try a gap of .45 thats where mine seems happiest.
try a gap of .45 thats where mine seems happiest.
Thread Starter
Instructor
Joined: Jul 2003
Posts: 118
Likes: 0
From: Twin Lake Mi
At this point, I have not tried the points & condensor. I don't know what the previous owner used in the engine but it apparently isn't quite stock. When I first got it I tried to check the timing & was not able to with my timing light. I had the vacuum lined plugged & the timing mark was moving all over. It would not set still so I could see where I was at. I ended up taking it to the Chevy dealer & had them set the timing & points.
Corvette Stories
The Best of Corvette for Corvette Enthusiasts
150 hp to 1,250 hp: Every Corvette Generation Compared by the Specs That Matter
Joe Kucinski
8 Coolest Corvette Pace Cars (and Replicas) of All Time
Verdad Gallardo
Top 10 Corvette Engines RANKED by Peak Torque (70+ Years of Muscle!)
Joe Kucinski
Corvette ZR1X Will Be Pacing the Indy 500, And Could Probably Race, Too!
Verdad Gallardo
Top 10 Corvettes Coming to Mecum Indy 2026!
Brett Foote
Top 10 C9 Corvette MUST-HAVES to Fix These C8 Generation Flaws!
Michael S. Palmer
10 Revolutionary 'Corvette Firsts' Most People Don't Know
Joe Kucinski
5 Reasons to Upgrade to an LS6-Powered Corvette; 5 Reasons to Stay LT2
Michael S. Palmer
2027 Corvette vs The World: Every C8 vs Its Closest Competitor
Joe Kucinski
Melting Slicks
Joined: Mar 2006
Posts: 3,342
Likes: 7
From: Connecticut
When I bought my 73' the Valve guide seals were in bad shape and the engine only had 2,000 miles on a rebuild.
Problem is that it sat for 11 years.
I talked to a local Vette shop (this guy knows his stuff , very well respected but also very expensive)
He said if you dont want to change the seals right now change the spark plug#.
I took his advice, I switched from AC Delco R45T to R45TS
The plug is a little longer than the T which will keep them from fouling.
Everytime I pull one they look PERFECT.
So it smokes for 15 seconds after its been sitting for half a day or more but it rund like a clock.
Im not sure If I want to go with new guide seals or smaller chamber heads so I havnt done anything about it yet........ that will be the next project, new guide seals or new heads......... Hmmmm... what would you guys do?
Problem is that it sat for 11 years.
I talked to a local Vette shop (this guy knows his stuff , very well respected but also very expensive)
He said if you dont want to change the seals right now change the spark plug#.
I took his advice, I switched from AC Delco R45T to R45TS
The plug is a little longer than the T which will keep them from fouling.
Everytime I pull one they look PERFECT.
So it smokes for 15 seconds after its been sitting for half a day or more but it rund like a clock.
Im not sure If I want to go with new guide seals or smaller chamber heads so I havnt done anything about it yet........ that will be the next project, new guide seals or new heads......... Hmmmm... what would you guys do?
Melting Slicks
Joined: Mar 2006
Posts: 3,342
Likes: 7
From: Connecticut
Originally Posted by Amature
When I first got it I tried to check the timing & was not able to with my timing light. I had the vacuum lined plugged & the timing mark was moving all over. It would not set still so I could see where I was at. I ended up taking it to the Chevy dealer & had them set the timing & points.
Something doesnt sound right at all.
I wouldnt blame leaking valve guide seals on lousy performance unless it smokes constantly, and even then, it could be a much deeper issue than seals.
What did the dealer say about the timing problem??????
I would love to know.
Burning Brakes
Joined: Jun 2004
Posts: 872
Likes: 3
From: Cortlandt Manor New York
You really need to get soomeone who knows what they are doing to look at this car. The timing mark shouldn't be jumping all over the place. If the cap and wires were replaced do you have wires crossed? How did it run after the dealer timed it? If it ran good then what was done after that? You are replacing everything but fixing nothing. You have to have someone find out what the problem is.
Pro
Joined: Dec 2004
Posts: 570
Likes: 0
From: glace bay nova scotia
paul 67,what i meant was,a good compression test would indicate a seal rather than a burnt valve or ring.
If the compression test revealed a low cylender,then he doesn't need to worry about seals,he has bigger problems.
sorry about the wrong info regarding the points,i missed the year of the vehicle.
If the compression test revealed a low cylender,then he doesn't need to worry about seals,he has bigger problems.
sorry about the wrong info regarding the points,i missed the year of the vehicle.
Le Mans Master
Joined: May 2006
Posts: 9,993
Likes: 1,136
From: League City Tx
I recently changed the valve seals in both my 71 sb and my dad's 69 BB. Both were smoking on start up and at hot idle. It was pretty often that both of them would start smoking at any given time. Both were fouling plugs. I changed the valve seals with the heads still on the car, takes 3 hrs or so about about $30 for seals and spark plugs. I would try that first, I am sure thats your problem. Put air in the cylinder to hold the valves up.
Both of our cars run well and do not smoke at all, neither has fouled a plug yet either in about 500 miles
Both of our cars run well and do not smoke at all, neither has fouled a plug yet either in about 500 miles
Melting Slicks
Joined: Mar 2006
Posts: 3,342
Likes: 7
From: Connecticut
I have a question
I need to remove my Intake manifold to re seal it..Its leaking a little oil so Im guessing its also leaking vacuum?
Anyhow
With the intake removed is there a way to hold the valves up? (I'm trying to picture this in my head)
I dont trust my antique compressor to hold air long enough to do the job
The compressor is 220 and I dont have 220 in the garage nor do I have a couple hundred feet of hose to make it to the garage.
So... where do I stand with the intake manifold removed?
Thanks!
I need to remove my Intake manifold to re seal it..Its leaking a little oil so Im guessing its also leaking vacuum?
Anyhow
With the intake removed is there a way to hold the valves up? (I'm trying to picture this in my head)
I dont trust my antique compressor to hold air long enough to do the job
The compressor is 220 and I dont have 220 in the garage nor do I have a couple hundred feet of hose to make it to the garage.
So... where do I stand with the intake manifold removed?
Thanks!
Melting Slicks
Joined: Mar 2006
Posts: 3,342
Likes: 7
From: Connecticut
Originally Posted by ajrothm
removing the intake will not affect the valves since you are not taking off the rocker arms and valve springs.
I was trying to think if I could grab the pushrod somehow and keep the valve up but I guess that would do just the opposite
Le Mans Master
Joined: Oct 2004
Posts: 5,269
Likes: 54
From: Orlando Florida
St. Jude Donor '05
Does the spark plug you're suspecting look different than the other 7 ?
Does the engine consume oil ?
IF the valve seal is bad you'll see the burnt oil on the plug.
Your balancer seems to be slipping, that's likely why your timing mark moves. This seems to be very common, a new balancer is however relatively inexpensive.
Any spark plug listed in the parts store's catalog should be fine. there may be some performance differences but any of these, no matter what brand should be good enough to get the engine running without missing....
It could be as simple as a weak coil.
Before you go to a shop: This is a simple Chevy small block engine, they made gazillios of these. It's not a Corvette specific problem that requires a "Corvette expert" who charges $150/hour.
Does the engine consume oil ?
IF the valve seal is bad you'll see the burnt oil on the plug.
Your balancer seems to be slipping, that's likely why your timing mark moves. This seems to be very common, a new balancer is however relatively inexpensive.
Any spark plug listed in the parts store's catalog should be fine. there may be some performance differences but any of these, no matter what brand should be good enough to get the engine running without missing....
It could be as simple as a weak coil.
Before you go to a shop: This is a simple Chevy small block engine, they made gazillios of these. It's not a Corvette specific problem that requires a "Corvette expert" who charges $150/hour.
Thread Starter
Instructor
Joined: Jul 2003
Posts: 118
Likes: 0
From: Twin Lake Mi
I did finally manage to get the car into another garage. In my haste, I had crossed a couple of the new plug wires I installed. That wasn't the big problem though. They found the distributor was shot. When they tried to get at the points, the plate was moving. They said a lot of people like to use chassis grease in the distributor when they rebuild them. It tends to get sticky & grabs enough that the bearing spins in the housing. They rebuilt the distributor , put in new points & plugs & retimmed it. It runs a lot better now. I still think I have an oil fouling problem though. I will check that Friday. They didn't see that since I had removed the deposits from the worst plug.
Melting Slicks
Joined: Mar 2006
Posts: 3,342
Likes: 7
From: Connecticut
Originally Posted by Amature
the timing mark was moving all over. It would not set still so I could see where I was at. I ended up taking it to the Chevy dealer & had them set the timing & points.
Originally Posted by Amature
I did finally manage to get the car into another garage. They found the distributor was shot.
