Trying to solve a LT-1 engine problem

[Ronald D.]

Re: Trying to solve a LT-1 engine problem

It sounds like your leak is from one of the heads and you have had the same problem with two other sets of heads. Of the other four heads, do all of them leak or can you use one of them along with the non-leaking head of the present set? Hardened valve seats are a bad idea because of the risk of cutting into the water jacket, but it is not a 100% risk. Of six heads, you should have two that do not leak.

Patrick the original heads that came with the car in 1971 were rebuilt with new seats, one of them was bad, I found a complete matching set with good date codes also rebuilt with new seats, one of those is leaking, my first one I sold since I had a matched set, now one of those is bad, and the other one I think doesn't leak, I will find out in a few days after I remove the manifold and get it under pressure, if I find a new or replacement head I will have to swap out the valves, springs etc to the replacement one, then I can hope it isn't bad also, my luck with heads isn't very good, and yes I will not have hardened seats installed

[Duke W.]

Re: Trying to solve a LT-1 engine problem

I'll add that correct casting number heads are more likely to have the 1.94/1.5" valve sizes than the 2.02/1.6" sizes that were unique to the LT-1 in those years. In such a case retain the standard valve sizes rather than grinding out the seats to the larger valve sizes. The difference in power is minimal.

If you want "more power" than OE, massaging the heads is the way to go. The best flow data I have in my library is a very well massaged set of big port heads that have the standard valve sizes. They outflowed all the massaged SHP heads with the big valves.

Duke

[Ronald D.]

Re: Trying to solve a LT-1 engine problem

Duke, thank you I have been looking, the problem is the 1.94/1.5 valve heads have pressed in studs, and no push rod guide plates, when I get judged and they look in the oil fill hole it will be noticed, and I don't trust press in studs, that sort of takes me back to after market heads, they won't have date codes, or head markings in the ends, but will be correct when looking inside and I won't have this to deal with anymore, my only concern can I still get Top Flight with them installed, if yes thats what I will do, if not I won't, Ron

I'll add that correct casting number heads are more likely to have the 1.94/1.5" valve sizes than the 2.02/1.6" sizes that were unique to the LT-1 in those years. In such a case retain the standard valve sizes rather than grinding out the seats to the larger valve sizes. The difference in power is minimal.

If you want "more power" than OE, massaging the heads is the way to go. The best flow data I have in my library is a very well massaged set of big port heads that have the standard valve sizes. They outflowed all the massaged SHP heads with the big valves.

Duke

[Joe L.]

Re: Trying to solve a LT-1 engine problem

Duke, thank you I have been looking, the problem is the 1.94/1.5 valve heads have pressed in studs, and no push rod guide plates, when I get judged and they look in the oil fill hole it will be noticed, and I don't trust press in studs, that sort of takes me back to after market heads, they won't have date codes, or head markings in the ends, but will be correct when looking inside and I won't have this to deal with anymore, my only concern can I still get Top Flight with them installed, if yes thats what I will do, if not I won't, Ron

Ron------


You can have the heads with pressed-in studs converted to screw-in very easily. In fact, GM used the same castings for both type of heads. For the screw-in stud versions they machined down the rocker stud boss and installed the hex base screw-in studs. A machine shop can do exactly the same thing now. If you wish, you can even use the GM studs which are currently available under GM #10168410. Push rod guide plates can also be easily installed when this is done. They're GM #3973418.

[Michael W.]

Re: Trying to solve a LT-1 engine problem

fter market heads, they won't have date codes, or head markings in the ends, but will be correct when looking inside and I won't have this to deal with anymore, my only concern can I still get Top Flight with them installed, if yes thats what I will do, if not I won't, Ron

Best learn a little more about the judging system and point deductions. You're going down the wrong path.

[Ronald D.]

Re: Trying to solve a LT-1 engine problem

OK, I am going to locate a good casting, so long as its 3487 head, the problem one is passenger side so date codes won't be looked at just the outside casting marks, since the current heads have been milled a little I can have the old one, assuming the drivers side is ok, checked for the amount that was shaved and do the same to the new one, have the studs and valves springs transffered over then have it pressure tested before install

[Patrick H.]

Re: Trying to solve a LT-1 engine problem

You don't have to shave the replacement if it doesn't need it. Your engine won't care about the nominal difference between the two.

[Duke W.]

Re: Trying to solve a LT-1 engine problem

Like Joe said a set of standard valve heads can be easily converted to screw in studs/guideplates, and you can use the the existing parts from the scrapped heads. I'm assuming that you will replace both heads since the driver's side has exhaust valve seat inserts, which could be a problem in the future.

If the head and deck mating surfaces are flat as measured with a machinist's bar and .0015" feeler there is no need to machine them and a Felpro 1094 shim gasket should seal. Assuming you used OE replacement pistons, the actual CR is probably no more than 8.7:1 with a thin gasket and the engine should operated detonation free.

Using a composition gasket could drop the CR down to close about 8:1, which will leave a lot or torque, power, and fuel economy on the table. Whatever you buy you should check to see if the mating surface was machined in the field. This will be indicated by circular tool marks rather than broach marks, and it will also be a good idea to measure head chamber volumes and deck clearance on both sides to ensure that side to side CR difference is close to zero.

For low compression LT-1 rebuilds I recommend a set of big dome KB hypereutectic pistons to get the CR back up into the 10-10.5 range, which will be a significant performance and fuel economy enhancement - essentially gets the engine back to the '70 high compression configuration and unleaded pump premium will work fine without any significant detonation.

Also, converting the ported vacuum advance to full time and retuning the spark advance map to 365/375 HP spec will do wonders to performance and fuel economy.

Duke

[Ronald D.]

Re: Trying to solve a LT-1 engine problem

Update, I located a replacement head, only the right side had issues, it goes to the machine shop next week, it's all original never been rebuilt, once I get it to the shop they will check for cracks, if all is OK, I plan on removing the valves, springs, studs and guide plates I am hoping this will fix my problem, thanks for all the input, Ron

[Ronald D.]

Re: Trying to solve a LT-1 engine problem

It looks like Edward hit the nail on the head, what happened was the system had more coolant in the right exhaust system from the prior valve seat leak that I thought. I removed the valve covers, no water, I removed the exhaust manifolds, and spark plugs and pumped up the cooling system to 15 pounds, it held for 90 minutes, no leaks, no loss in pressure, it wasn't a complete loss of time, when I installed the heads last time I used exhaust manifold gaskets from manifold to head, I wanted to remove them so it would be correct anyway. One thing I am not looking foreward to years from now is replacing the spark plugs on the drivers side the heat shields are almost impossible to work with, it looks like removing the manifolds is the best way to get to the plugs, not the best design, but in the 70's there was a lot of that.

Ron, it best to make sure that no coolant is left in the system, If the car is registered take for a drive, keeping a eye on the temp. make sure coolant level is topped off. after the test if all clears up you should be good to go. I myself have done hundred if not a few thousand head gaskets job. over the years and if coolant has entered the exhaust system its can take a good long road test to heat the exhaust system enough to burn off the antifreeze.

[Terry M.]

Re: Trying to solve a LT-1 engine problem

It looks like Edward hit the nail on the head, what happened was the system had more coolant in the right exhaust system from the prior valve seat leak that I thought. I removed the valve covers, no water, I removed the exhaust manifolds, and spark plugs and pumped up the cooling system to 15 pounds, it held for 90 minutes, no leaks, no loss in pressure, it wasn't a complete loss of time, when I installed the heads last time I used exhaust manifold gaskets from manifold to head, I wanted to remove them so it would be correct anyway. One thing I am not looking foreward to years from now is replacing the spark plugs on the drivers side the heat shields are almost impossible to work with, it looks like removing the manifolds is the best way to get to the plugs, not the best design, but in the 70's there was a lot of that.

While Gen 1 spark plugs, especially 1970 with all four ignition shields over the plugs, can be a pain; Gen II LT1 from the 1990s is no less so. And the Gen IIs don't even have ignition shielding. Changing the spark plug wires on Gen I is far easier than on the Gen II. And we won't even talk about distributors. Enjoy what you have Ron, it could be worse.

PS: I am glad you found your problem. Thanks for posting about your solution. It will help others down the road.

[Edward J.]

Re: Trying to solve a LT-1 engine problem

While Gen 1 spark plugs, especially 1970 with all four ignition shields over the plugs, can be a pain; Gen II LT1 from the 1990s is no less so. And the Gen IIs don't even have ignition shielding. Changing the spark plug wires on Gen I is far easier than on the Gen II. And we won't even talk about distributors. Enjoy what you have Ron, it could be worse.

PS: I am glad you found your problem. Thanks for posting about your solution. It will help others down the road.

Terry, been there, done that, gen 2 LT1 tune ups are no picnic, It's a two 6 pack type job,

[Joe L.]

Re: Trying to solve a LT-1 engine problem

It looks like Edward hit the nail on the head, what happened was the system had more coolant in the right exhaust system from the prior valve seat leak that I thought. I removed the valve covers, no water, I removed the exhaust manifolds, and spark plugs and pumped up the cooling system to 15 pounds, it held for 90 minutes, no leaks, no loss in pressure, it wasn't a complete loss of time, when I installed the heads last time I used exhaust manifold gaskets from manifold to head, I wanted to remove them so it would be correct anyway. One thing I am not looking foreward to years from now is replacing the spark plugs on the drivers side the heat shields are almost impossible to work with, it looks like removing the manifolds is the best way to get to the plugs, not the best design, but in the 70's there was a lot of that.

Ronald------


Ever wonder why you see a lot of Corvettes missing the spark plug ignition shielding? That's why. However, removing and re-installing the shielding really isn't all that bad once you get the hang of it.

[Mark E.]

Re: Trying to solve a LT-1 engine problem

Ronald------Ever wonder why you see a lot of Corvettes missing the spark plug ignition shielding? That's why. However, removing and re-installing the shielding really isn't all that bad once you get the hang of it.

It's surprising, but I find replacing spark plugs on big blocks to be easier than small blocks. And of course, it's much easier to change BB plug cables.

[Mark E.]

Re: Trying to solve a LT-1 engine problem

Ron,
I did the plug out at the dealer and the customer insisted on watching. It was a straight 6 cylinder and when I turned it over the water came out the spark plug hohe and blew his glasses off.Dom

Really? That's too funny. Who knew that kind of pressure and volume could develop.