We rebuilt our L78 solid lift engine and have some vibration issues and a semi rough idle. The break in oil was Rotella 10-30 with Lucas Break in zink additive. Ran from 2000 - 2200 RPM for 20 minutes. I did have an issue with fuel and had to do several start attempts with more than normal cranking prior to the 20 minute run. Rings seated after about 5 minutes and everything seemed OK. Let it cool for a couple hours and start it with mild vibration but from 800 - 2000 it is very rough idle. Starts great no back fire timing responds fine. Has a stock distributor and dwell stays at 30. I do not here any strange noises but the solid lifter flat tappet make a lot of noise.
During Break-in 396 vibration problems
copol78
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We rebuilt our L78 solid lift engine and have some vibration issues and a semi rough idle. The break in oil was Rotella 10-30 with Lucas Break in zink additive. Ran from 2000 - 2200 RPM for 20 minutes. I did have an issue with fuel and had to do several start attempts with more than normal cranking prior to the 20 minute run. Rings seated after about 5 minutes and everything seemed OK. Let it cool for a couple hours and start it with mild vibration but from 800 - 2000 it is very rough idle. Starts great no back fire timing responds fine. Has a stock distributor and dwell stays at 30. I do not here any strange noises but the solid lifter flat tappet make a lot of noise.
I pulled the plugs. # 1 looks new (my son installed the plugs and this one may have not been fully seated) # 2 thru 7 look normal with light tan color. # 8 looks fowled burnt with black carbon fully covering the end of plug. The plugs are AC Delco R43XLS. The heads are 3964291 1970 BB heads.
I would re install all of the plugs and take it for a drive if the car is mobile.
The plugs will probably be fairly sooty looking and wet unless you do a WOT pull and shut down as that's how you read plugs.
It is an outlier that you have a plug that does not look like the others, it could be anything at this point. Make sure your plug wires are snapped firmly on the cap, and plugs, check for vacuum leaks as well. Make sure all the vacuum ports are capped off that aren't being used.
The plugs will probably be fairly sooty looking and wet unless you do a WOT pull and shut down as that's how you read plugs.
It is an outlier that you have a plug that does not look like the others, it could be anything at this point. Make sure your plug wires are snapped firmly on the cap, and plugs, check for vacuum leaks as well. Make sure all the vacuum ports are capped off that aren't being used.
Thanks AJ.....Cannot drive the car yet. We did a frame off and still have work to complete. One thing that I worry about is cam lobe damage. This would by my first after 12 restorations. I always follow the same process on break in. Same engine builder on 12 big blocks. One note is my 499 distributor was repaired on the area where the point mount plate sits on the sleeve. Repair looks solid but could be a variable. There was so much vibration oil started leaking from the front timing cover seal at harmonic balancer.
How is the engine being run? On the subframe or some kind of stand?
I'm not sure if you installed a larger cam, and if stock, I'm not super familiar with the specs on the l78, but even larger cams should smooth out around 1,500-1,800rpm. Some shaking is normal, most of these engines will rock in the engine bay, and shake the car pretty well, I know mine does, but it should smooth out.
It may be worth finding and HEI or something simple to install to rule out the distributor.
A flat cam is very possible, but unless you just got a bad core, or have a lot of valve spring, it's probably ok... Comp had a bunch of bad cores pre '08 I believe, but it is possible.
Can you back off of the rockers and get a telescoping magnet and pull out the lifters? I've had to do this before when a link bar broke on a dragster engine in between heats... I'm not sure if the iron heads have as much space to do so as the new heads do, but if you think it could be a lobe, I would try that and pull them out 1 by 1 and re install. You may be able to tell if the cam is bad by taking the pan off and looking up at the cam. Drain the oil through a screen as well and report back.
I'm not sure if you installed a larger cam, and if stock, I'm not super familiar with the specs on the l78, but even larger cams should smooth out around 1,500-1,800rpm. Some shaking is normal, most of these engines will rock in the engine bay, and shake the car pretty well, I know mine does, but it should smooth out.
It may be worth finding and HEI or something simple to install to rule out the distributor.
A flat cam is very possible, but unless you just got a bad core, or have a lot of valve spring, it's probably ok... Comp had a bunch of bad cores pre '08 I believe, but it is possible.
Can you back off of the rockers and get a telescoping magnet and pull out the lifters? I've had to do this before when a link bar broke on a dragster engine in between heats... I'm not sure if the iron heads have as much space to do so as the new heads do, but if you think it could be a lobe, I would try that and pull them out 1 by 1 and re install. You may be able to tell if the cam is bad by taking the pan off and looking up at the cam. Drain the oil through a screen as well and report back.
Good input. The engine is sitting in a project that has just been through a frame off. Today was the first start up and break in. I have owned about 10 of these 396 and 427 solid lifter motors that went through a rebuild. This vibration is not normal......too rough at acceleration from idle to 2000. The cam specs are the stock 396-375 HP for 1969 made by comp cam. I have another distributor that I will swap out. My plan is install different distributor, new plugs, adjust valves again, drain oil and screen with a paint strainer. Then I can set points, set timing and check manifold vacuum. Run engine and report back. Did I miss anything?
A 396/427 are neutral balanced, 454's are externally balanced.
Could any 454 parts gotten installed?
I would run a 44 spark plug.
Use a temp gun and shoot each exhaust runner when engine is cold in finding a lower temp cylinder - one not firing or getting too much/too little fuel.
Cast iron intake or alum intake?
Either way, is the chosen one seated against the heads?
If alum is chosen, the supplied rubber ends used, the alum manifold may be warped from bolt torque and not sealing against the head making for a lean cylinder - temp gun on exhaust manifold port will find this as a lower temp.
Could any 454 parts gotten installed?
I would run a 44 spark plug.
Use a temp gun and shoot each exhaust runner when engine is cold in finding a lower temp cylinder - one not firing or getting too much/too little fuel.
Cast iron intake or alum intake?
Either way, is the chosen one seated against the heads?
If alum is chosen, the supplied rubber ends used, the alum manifold may be warped from bolt torque and not sealing against the head making for a lean cylinder - temp gun on exhaust manifold port will find this as a lower temp.
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I would replace the dark sooty spark plug. Also check the ohms on the spark plug wire and another one the same length. Pull the harmonic balancer check behind the harmonic balancer for a weight bolted to the inside. If an auto trans. check the flexplate for any weights also.
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1,424 Posts
Here are a couple of ways to adjust the valves with the engine off. http://www.centuryperformance.com/valve-adjustment-procedure.html Another way is EO/IC. Exhaust opening, intake closing.
Example;
You are working on cylinder #1,.... Rotate the engine by hand until you see the #1 exhaust lifter just start to open. Stop there and set the lash for the intake valve. Continue to rotate the engine by hand. Now the intake lifter will rise, go to max lift and start closing. Stop there and adjust the lash for the exhaust valve. Repeat for the other 7 cylinders.
On any cam, when the exhaust valve just starts to open, the intake lifter will be on it base circle and ready to be lashed. When the intake valve has opened and is starting to close, the exhaust lifter will be on it's base circle of the cam and ready to be lashed. That lash setting will be spec'd with your particular cam. I prefer the EO/IC for adjusting solid lifters or mechanical roller lifters. My machinist showed me this procedure many years ago and I have used it ever since. BTW if you have aluminum heads and cast iron block subtract .006 from your cold lash. After starting my engine and running until normal temperature I shutdown and rechecked the lash, it was dead on what the camshaft company recommended. With the engine cold my lash was .020" & .022" after subtracting .006 and then after running it was .026" & .028". Unreal ain't it.
Example;
You are working on cylinder #1,.... Rotate the engine by hand until you see the #1 exhaust lifter just start to open. Stop there and set the lash for the intake valve. Continue to rotate the engine by hand. Now the intake lifter will rise, go to max lift and start closing. Stop there and adjust the lash for the exhaust valve. Repeat for the other 7 cylinders.
On any cam, when the exhaust valve just starts to open, the intake lifter will be on it base circle and ready to be lashed. When the intake valve has opened and is starting to close, the exhaust lifter will be on it's base circle of the cam and ready to be lashed. That lash setting will be spec'd with your particular cam. I prefer the EO/IC for adjusting solid lifters or mechanical roller lifters. My machinist showed me this procedure many years ago and I have used it ever since. BTW if you have aluminum heads and cast iron block subtract .006 from your cold lash. After starting my engine and running until normal temperature I shutdown and rechecked the lash, it was dead on what the camshaft company recommended. With the engine cold my lash was .020" & .022" after subtracting .006 and then after running it was .026" & .028". Unreal ain't it.
Excellent input.
FYI I drained the oil and screened using a paint strainer and found zero metal flakes. PTL.......
I adjusted all the valves and found 7 opened from .024 to .030 gap. All others were as set prior to running. Thought I would install new set of plugs and different dist. cap rotor. (all these on the car were used off an older dist. assembly I had). I will buy a temp gun and do that test. SO at this point thought I would re assemble, set timing/dwell and try again. Thanks to everyone for support! If vibration still exist I will pull balancer.
FYI I drained the oil and screened using a paint strainer and found zero metal flakes. PTL.......
I adjusted all the valves and found 7 opened from .024 to .030 gap. All others were as set prior to running. Thought I would install new set of plugs and different dist. cap rotor. (all these on the car were used off an older dist. assembly I had). I will buy a temp gun and do that test. SO at this point thought I would re assemble, set timing/dwell and try again. Thanks to everyone for support! If vibration still exist I will pull balancer.
I changed the oil/filter and screened the old oil.....did not find any traces of metal (even used a telescope magnet inside oil pan drain plug). I installed a new # 8 plug and new rotor cap. Purchased a rebuilt dist. from auto parts store but could not get it to fire so I installed the old dist and engine fired right up. Idle is good....no backfire through carb or exhaust. Manifold vacuum is 9-10. Still have serious vibration from 1000 up to 1800. Motor acts like it has 3 plug wires off
Mabey next step is to check balancer to see if it is a 454.
Mabey next step is to check balancer to see if it is a 454.1 - 20 of 33 Posts
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