Dan H.

Hello all,
I have a 50k mile '71 LT-1. Was driving to work and a couple weird things happened. Got on the highway and suddenly I'm getting what I call the leaky exhaust old pickup truck noise. This is where you hit the gas and have the loud chugging exhaust noise, and when I let off the gas, no loud noise. I pull off to the rest stop and pop the hood.

I am looking around the manifold/exhaust pipe flange looking for a leak. I take an old shirt and mess with the heat riser while its running and it doesn't effect the noise at all. What I found is that I have the typical lifter noise on the driver side. However, I am getting a ton more noise out of the passenger side valve cover. Forgive my newbie reference here, but it sounds like I poured the change jar in the valve cover and put it on the car. Valve noise was much louder out of the passenger side versus the driver side.

So got the car towed home a couple days ago, tonight i popped a valve cover to poke around and found this. Looks like a spring retainer is cracked halfway around (see pic). Also, all the rocker arms seem loose. I would imagine that one or two should rock a little since some should be closed, however, several of these are loose at once, is there a problem here? (see the attached video)
http://youtu.be/JaRttYOmVSo

Car sat for 10 or so years without running. I have heard that some springs sitting compressed while other have no compression can cause problems, is this one of them???

63mako

LT1 is solid lifter cam. The valves that are closed should have some play or rock. They will feel loose. That damage could come from not adjusting the lash and running it to loose. #2 intake looks really loose. That will take the cam lobes and lifter bottoms out as well usually requiring a complete rebuild. Have you set the lash recently? Was it done correctly? It is a routine maintainance item with your cam. Are you using a high ZDDP oil or regular oil. If you are using regular oil I will bet you have wiped cam lobes.

Dan H.

Running Amsoil 10-40 high ZDDP oil since I have owned it, which is only the past 1.5 years. In that time, I've only driven 1000 miles. Prior to me it sat for 10 years without running. Before 10 years of storage, it was changed twice a year with regular castrol gtx 10-40. Not sure when zinc was removed........

63mako

Oil isn't the issue. Could be fatigued springs as you suspect. Hope the cam is ok. I would adjust the lash and turn the engine over by hand and see if all the valves go up and down the same amount visually. If so change out the springs, adjust the valves and drive it to see if your good.

Dan H.

63mako, Thanks for the advice, appreciate it. I'll turn it over and check the movement in the next couple nights and report back.

63mako

http://www.lbfun.com/warehouse/tech_...n/SBvlvadj.pdf
Cold lash adjustment procedure. Lash adjustments are difficult with these due to the long duration. Typical adjustment procedure used with hydraulic cams and inserting a feeler guage will result in to wide of lash since the lifter will not be on the base circle when you think it will. Follow these instructions exactly.

Dan H.

63mako,
I've read through the instructions and it sounds straight forward. Thank you for sending and for your help!

One thing I'm fuzzy on is where am I measuring? Am I measuring the gap between the rocker arm and the end of the valve stem? Or am I supposed to measure somewhere else?

69 Chevy

Yes.

1971 LT-1 solid lifter cam specs are .024" intake and .030" exhaust HOT clearance NOT the 30-30 or so called 30 across cam specs. Measurements are taken with the engine at operating temperature.

You should really do both engine banks while you're at it.

To me, it looks like the umbrella is damaged, not the retainer.

63mako

Cold settings are .016 intake and .023 exhaust as shown in the instructions.

Dan H.

Over the weekend I turned the motor by hand and had good movement on all the valves. I'm going to replace the umbrella/shield and o-rings on cylinder #2 (where the cracked umbrella is). I also get build up on the plug from #2 spark plug making me think I have a disintegrated o-ring. I think I should replace the umbrella/shield, lock nut, and o-rings on both the intake and exhaust valve. The rocker arms were all very loose.

Next steps are to get a piston stop, get #2 to the top of the stroke, pressurize the cylinder, and remove the umbrella retainer and o-rings.

My big question, is where can I get these parts from? I have the corvette "parts and illustrations catalog" for 1953-1982. The part #'s in here don't get me any results online. I've looked at paragon, gmpp, jeg's, summit, rock auto, and none of them get me these part #'s.

69 Chevy

You might give A&A Auto Stores in BETHLEHEM a call. 610-821-0303 You'll need to ask for the required parts by name rather than those obsolete GM part numbers.

A mechanical piston stop isn't needed to make sure the valve doesn't fall into the cylinder bore although I think A&A can get one for you.

Lt1er

If you were smart you would improve the 50 year old design. Modern Valve springs and chrome moly retainers with 10 degree locks are cheap. Your old crap springs lost their tension long ago and those rotators and umbrellas are a very poor design.

I just run better springs from Comp Cams along with the roller tipped rockers

Put all that old stuff in a bag.

cv67

Lt1er

63mako

A new set of Elgin Z28 springs and retainers will do it.
http://www.ebay.com/itm/Z28-Valve-Sp...e226d3&vxp=mtr
Cheap and easy. Set them up @ 1.700 and your good to go. New seals while your at it and a good valve adjustment (see link.)

Dan H.

Sorry about the lack of updates guys, I have been traveling for work for the last week (and very happy to finally be home).

I am certainly not opposed to changing all the springs, retainers, and locks. I agree that over time, these things loose their tension.

I can follow the directions and adjust these per the link. Are these parts on ebay what I need? If these are the exact ones, I will pick them up and install them. I think that the nuts need to be replaced as well as the o-rings. Not sure if these are single use or not, but I don't want them to back off.

Also, how do I set them to 1.700 as you stated?

Any tricks to marking the harmonic balancer with degree marks? The adjustment procedure has me adjusting at 0, 90, 180, and 270.

I'd like to thank the person that recommended A&A in Bethlehem. I went there today and it was refreshing to talk to someone behind the counter that understands a 350.

63mako

The springs I recommended will be fine. They are the typical replacement spring for factory solid flat tappet cams and are made in usa last I knew.
http://www.lunatipower.com/Tech/Valv...pringTech.aspx
I use a flexable tape measure like a taylor would use. Wrap it around the balancer and divide circumference by 4. Mark with chalk. Lash is measured between the rocker tip and valve end.
http://www.summitracing.com/parts/CCA-4604-16/
I like poly locks on solid cams. They hold adjustment and are reuseable

Dan H.

Hey guys, Finally able to spend some time in the garage.

So I took some video of the valve stem movement in the guide. I don't know if this is a lot or a little, I'm learning as I go (which has made this slow, but fun). This is cylinder #2 both intake and exhaust. Can you guys take a look and let me know what your opinion is?

http://youtu.be/O685z7pMvMw

The o-rings were still on both the valves. They were brittle and cracked when I removed them. I found that on the exhaust valve, the plastic umbrella had a chunk missing.


Here is the cracked metal umbrella removed


I picked up new springs, retainers, and locks. I don't know if this is a big deal or not, but unsprung these are different heights.

63mako

That is a lot of play at the guide. Typical new guide to valve stem clearance would be about .002 which is .001 on each side. I know you don't want to hear this but I would pull the heads and get new guides installed, valves and seats ground, seals and have the new springs set up at proper install height by a quality machine shop. This will not be a real expensive job. It will also give you a chance to check the condition of the cam and lifters. Before reassembly check your pushrods, rockers and rocker ***** and seats. Then you know the top end is solid which is critical in a solid lifter flat tappet cam engine. Make sure all components stay matched to their current location. The difference in spring height in the photo is a non issue. Your stock springs may well have been the same height new. 40 years of being under load will do that.

Dan H.

I was thinking it was to much wobble also, but I don't have the experience to know for sure. Thank you for your response. Most may see this as bad news. I'm looking forward to taking it apart and getting everything is good running order. It'll suck to have it apart for a couple months, but it comes with the territory of a 40 year old car.

I just have to make sure I take my dads car out when I go upstate to get some hot rod seat time!

63mako

SWEEEEEET!!!!
An LT1 with 50,000 deserves proper mant and needed repairs done on a timely basis. You are using a High ZDDP oil right?