Flyinace3

I have a 1980 Corvette with a 350 gm crate engine that I installed about 5 years ago. It started to smoke at idle and getting worse. I did a compression check and my lowest cyl is 200psi and my highest is 210 psi. The engine has about 1500 miles on it. The engine specs are as follows.
350 cu in
Dart shp 180 heads
Comp Cams hyd roller extream energy 276hr
1.6 scorpion roller rocker arms
Edelbrock performer rpm
Quick fuel 650 double pumper.
Compression is 9.8 to 1

Today I removed 2 valve springs to look at the seals. The seals look good except that the small spring on the seal has rode up and dislodged from the valve seal..any idea why this would happen? The valve ride smooth in the guides as well ..
I will try to post some pics for the experts to look at

https://photos.app.goo.gl/DeNvdcp1w7LdZinJ7

derekderek

Pull the seals. Get a dial caliper and measure dia and height of surface cut on exterior of guides for the seals. Buy 16 new ones. At least replace the intake seals. Exhausts sometimes dont even get seals. Almost want them to get a little oil.

vince vette 2

Not an expert, but my understanding and experience is that bad valve seals usually result in just a puff of smoke on start up due to oil build up when the engine is off and residual oil on the valve caps, tops of seals, and valve stem flowing down to and into the valve stem guide. When running the amount of oil that could enter on each cycle would seem to be too little to allow enough to enter the cylinders to be seen in the exhaust. This would be especially true if the issue is just with jone or two cylinders I would think.

REELAV8R

I have a set of dart SHP heads that I have since removed from my 350 and am now running AFR heads.

Where to start with those darts?

The valve spring pockets are too shallow. This allows the springs to move around during operation. In my case it dislodged the valve seals on several occasions.
The distance from coil bind when the valve is at full lift is too great. This allows for spring surge and loss of control of the valve and wears on the guides excessively.

The installed height of the assembled heads is all over the place making for inconsistent seat and open pressures.

I would remove all the springs and measure you valve stem deflection at the top of the guide to check for guide wear.

I would also get inside locators for the springs and measure installed height and set them all even or close as possible with a shim set.

If your lucky the guides are not too badly worn yet.

Dart will not admit to an issue with these heads, but it exists.

Flyinace3

Thanks rev I was hoping you would chime in on this ..I will check the side wear with a dial indicator and the installed spring height... Do the seals I have look the same as what your dart heads had from the factory? I can not tell if the spring is bouncing. I had Steve saanche from total flow set the heads up for me when I bought them. I also ordered a leak down tester and will test each cylinder for the percentage.. I will keep everyone up to date on this... How have the AFR heads been treating you so far?

As a side note I did change the intake manifold 3 times with 3 different new Edelbrock intakes and about 10 gasket sets later . I used felpro and mr gaskets, gaskets the normal and thick gaskets as well trying to resolve the smoking issue...

REELAV8R

Yep same seals as mine.

Night and day difference between the Dart and the AFR heads as far as quality goes. Those advertised 180 Darts are more in the 190+ range.

AFRs dead on 180 cc’s.

darts chamber advertised 64 cc measured closer to 67 cc’s.

Only wish I had bought the AFR first time around. But the Darts did give me the opportunity to learn a bit about porting and practice some. And give me some perspective on middle of the road quality vs good quality manufacturing on heads.

The groove in the shim where the valve spring sits looks to indicate that the spring is moving around a lot.

gg521

Your spring dampeners are chewing into the shims. Yes, you more than likely have excessive spring movement. To fix this, I would employ the use of spring locators. These are available from a variety of sources ( Comp Cams, PAC, Manley, etc.). Measure the guide bosses and the spring pockets to find the correct locators. This will fix the valve stem seal issue too.

Flyinace3

I placed a order for new valve seals and spring locators from summit
COMP Cams 4771-16 - COMP Cams Valve Spring Locators
Dart 26000021 - Dart Valve Stem Seals

Also going to do a leak down test this weekend
Check installed spring height and valve side clearance ..

johnnied

take the springs off of the new seal before you install them, then put them back on

Flyinace3

Thank you I will do it that way

Flyinace3

My leak down tester came in today ..
I only had enough time to do two cylinders . 4&6 but the results look good to me
Cranking compression is
#4 207 psi
#6 210 psi
Leak down results
#4 8%
#6 10%

Vet76te

rebel542

I would guess that the spring came off during assembly. Roll it back in the groove and give it a try. Thats what I'd do. We are talking about a new crate engine. What else could it be?

Flyinace3

​​​​​The smoking issue happened recently. I installed the enengin 5 years ago and I put on about 2000 miles since then. It didn't smoke or use any oil recently.

Flyinace3

Good info . I did not think athink about that

Flyinace3

almost done with installing valvevspring locators and new seals. This is what I found on about half of them. The leak down test on all the cylinders is between 6 to 10%. I will post more info when I fire her up.

Jebbysan

Yes.....
Locators are mandatory on just about any head.....or spring locator cups.....
The I.D. locator to me are a better solution for 1.250 and 1.437 springs.......1.550 and 1.625 are fine with a cup as they have a large I.D.
It is crazy how many heads I have pulled apart and they are just using a hardened washer........anyone who would assemble stuff like that needs to be educated because it is just wrong.

Jebby

REELAV8R

Yep, same problem I had.

Shim up the springs so that they are closer to coil bind at full lift as well. This will help prevent spring surge which may also be contributing to unseating those valve guide seals.

REELAV8R

Dart apparently does not share your opinion. One I agree with, at least in my limited experience.

You would think that a company that has been around this long would know about such things.

Flyinace3

It's finished so far no smoking which I happy about. This winter I will pull the heads and either get new guides installed or just by afr's and be done with it.
thanks for all the help