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Have a new 383 sbc in my 71 convert with approx. 1800 mi. Installed some AFR heads over the weekend (replacing ProMaxx) and found two potentially concerning issues.
The first is the carbon build up. Too much for a young motor – see pics below. What could cause it? Is carbon due to burning oil? It did blue smoke a bit when new but that seemed to diminish lately. If so, know that is likely heads or rings. Valve guides/seals were checked and good, and can’t check oil rings, but compression and leak down numbers were good.
The second concern is with discoloration of the lifters. Pic below are the worst ones, but many have some degree of browning. Is that heat or bad oil? They slide well in the bores, and wear seems normal with mild vertical scuffing you cannot feel with your fingernail.
Car ran well, and did not overheat. Any tips would be greatly appreciated.
Some are better than others. Other bank looked similar. One of the worst examples. These are the worst examples of the discoloration. Others were not as bad.
2020 Corvette of the Year Finalist (performance mods)
2019 C3 of Year Winner (performance mods)
2016 C3 of Year Finalist
My 427 looked like that. The intake didnt deal. My commetic gaskets didnt let it seat fully and i dont usually use any sealant on the intake gaskets. When i dropped the 396 in as a temporary replacement i sealed both sides of the intake gaskets with nonhardening permatex #2. Big difference in idle
Have a new 383 sbc in my 71 convert with approx. 1800 mi. Installed some AFR heads over the weekend (replacing ProMaxx) and found two potentially concerning issues.
The first is the carbon build up. Too much for a young motor – see pics below. What could cause it? Is carbon due to burning oil? It did blue smoke a bit when new but that seemed to diminish lately. If so, know that is likely heads or rings. Valve guides/seals were checked and good, and can’t check oil rings, but compression and leak down numbers were good.
The second concern is with discoloration of the lifters. Pic below are the worst ones, but many have some degree of browning. Is that heat or bad oil? They slide well in the bores, and wear seems normal with mild vertical scuffing you cannot feel with your fingernail.
Car ran well, and did not overheat. Any tips would be greatly appreciated.
Some are better than others. Other bank looked similar. One of the worst examples. These are the worst examples of the discoloration. Others were not as bad.
Your lifter bores many not be perfectly round causing the discoloration. Just think about putting a piston in an oval can. There’s no vertical binding, but you’ll see the wear pattern where the piston’s sides touch the can walls.
I see many engine builders hone out the lifter bore for this reason.
Scotchbrite the scoring on the lifters...clean and reinstall.....the fine scrub marks you put on the lifter housing will retain a little oil...and will help with the scoring....which BTW, isn't bad.....these are spider lifters so what lift are you running and what spring pressures?
The carbon is definitely oil......what do the intake valves look like?
what brand gasoline do you use ?
what brand oil ?
Do the lifters clean up like it's varnish or are they permanently stained ?
does this engine "huff" much out of the valve covers when running if you pull the PCV valve from the valve cover ?
do you see any oil on the floor of the intake ports of the promaxx heads you just took off ?
Thanks everyone for the comments, and will post answers to the questions in the next day or so..
Always thought if the oil burning was bad intake sealing, it would not be so consistent across cylinders. Meaning a couple cyls would not have sealed and got sooty, but some would have sealed OK and looked clean, right? Mine weren't all to the same degree, but each cyl had soot for sure.
The seal on the ProMaxx heads and Edelbrock 2701 manifold was done with Felpro 1205 gaskets, RTV front and rear China walls, and thin RTV around the intake ports and water jackets.
However, might have found a smoking gun. Cleaned the mating surfaces of the intake manifold and flat filed them to remove any burrs or nicks made while prying it off (RTV made removal tough). Put each side of the manifold on a plate of glass and noticed slight rocking. Was able to slip a sheet of paper under the middle where the ports were with no problem. Both sides. Not precision measurements I know, but guessing a warped intake surface could affect sealing even with a thick gasket and RTV. In any case, bought a replacement manifold which arrives tomorrow.
Hoping that with new heads, manifold, gaskets, and using Permatex #2 around ports instead of RTV might do the trick. Been chasing this oil burning issue for longer than I care to admit.
Thanks everyone for the comments, and will post answers to the questions in the next day or so..
Always thought if the oil burning was bad intake sealing, it would not be so consistent across cylinders. Meaning a couple cyls would not have sealed and got sooty, but some would have sealed OK and looked clean, right? Mine weren't all to the same degree, but each cyl had soot for sure.
The seal on the ProMaxx heads and Edelbrock 2701 manifold was done with Felpro 1205 gaskets, RTV front and rear China walls, and thin RTV around the intake ports and water jackets.
However, might have found a smoking gun. Cleaned the mating surfaces of the intake manifold and flat filed them to remove any burrs or nicks made while prying it off (RTV made removal tough). Put each side of the manifold on a plate of glass and noticed slight rocking. Was able to slip a sheet of paper under the middle where the ports were with no problem. Both sides. Not precision measurements I know, but guessing a warped intake surface could affect sealing even with a thick gasket and RTV. In any case, bought a replacement manifold which arrives tomorrow.
Hoping that with new heads, manifold, gaskets, and using Permatex #2 around ports instead of RTV might do the trick. Been chasing this oil burning issue for longer than I care to admit.
Set the intake on with no gasket and observe.....then set it on there with gaskets and look again.....how does everything look.....look at the front and rear profile with no gasket, that is a big tell......
I asked what your intake valves look like.......and who built the heads.....it may have **** valve seals in it......crappy valve seals will make all cylinders carbon up.....
I asked what your intake valves look like.......and who built the heads.....it may have **** valve seals in it......crappy valve seals will make all cylinders carbon up..... Jebby
@Jebbysan To confirm, you are referring to bad seals that sit on the stems, and not the valve seats themselves, correct? If so, I replaced the seals on the ProMaxx heads with new ones when I put heavier springs on.
2020 Corvette of the Year Finalist (performance mods)
2019 C3 of Year Winner (performance mods)
2016 C3 of Year Finalist
editted as post above already stated they were checked prior for straightness.
If you arent sucking oil in through your intake gasket the only other way is tough the valve stem seals, the valve guides them selves,, or the PCV system
Last edited by Rescue Rogers; Jul 6, 2023 at 12:58 PM.
you can take the heads to a machine shop and have them decked to flatten them out...they can take just enough to get them flat without effecting compression and keep intake square
Already have new heads on the motor. Really trying to find the reason for the excessive carbon buildup.
2020 Corvette of the Year Finalist (performance mods)
2019 C3 of Year Winner (performance mods)
2016 C3 of Year Finalist
maybe your intake is warped. Can you clean up the heads and intake and put new gaskets and torque it down, then remove them and measure them for compression...see if the top and bottom crushed the same. I had an protruding head gasket keeping my intake from bottoming out
editted as post above already stated they were checked prior for straightness.
If you arent sucking oil in through your intake gasket the only other way is tough the valve stem seals, the valve guides them selves,, or the PCV system
Have eliminated the valve guides (were checked), seals (were replaced), and PCV as it has no indication of oil in the hose or coming in to the vacuum port on the back of carb. Also have good baffles in valve covers.. Thanks.
@Jebbysan To confirm, you are referring to bad seals that sit on the stems, and not the valve seats themselves, correct? If so, I replaced the seals on the ProMaxx heads with new ones when I put heavier springs on.
Yes....valve seals.....the ones to use are the blue Viton ones....Summit and Others sell them....they are made in Michigan at USeal EOK.....I really don't trust any other brand of seal and it is what most use....(Dart, AFR, etc....)
Yes....valve seals.....the ones to use are the blue Viton ones....Summit and Others sell them....they are made in Michigan at USeal EOK.....I really don't trust any other brand of seal and it is what most use....(Dart, AFR, etc....)
Jebby
Yes, the seals I installed were Viton seals. Guess I am back to the intake gaskets for the oil burning as have eliminated everything else but rings.
Put the current 2701 intake on the newly installed AFR heads with no gaskets, and they rocked a bit. Then test fit with the gaskets and it appeared to fit well. The ends had gaps of around 1/8" but were very level from side to side, so will be using RTV-only on those.
Yes, the seals I installed were Viton seals. Guess I am back to the intake gaskets for the oil burning as have eliminated everything else but rings.
Put the current 2701 intake on the newly installed AFR heads with no gaskets, and they rocked a bit. Then test fit with the gaskets and it appeared to fit well. The ends had gaps of around 1/8" but were very level from side to side, so will be using RTV-only on those.
I forgot to ask if the intake rocker studs were sealed were the go into the intake port....
Concerns with New Engine
