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1968 Malibu sport coupe, 489 ci. 590 hp 600 tq, RV T-400 Freakshow 3200 stall, 3.73 12 bolt posi
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I'd check all the push rods, doesn't Adv. a cam bring the exh. valves closer to the piston and Ret. the cam bring the int valves closer or is that the other way around?
 

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Discussion Starter · #22 ·
Not a builder, but I don't see how the guides in that bank can't be AFU as well. Valves were likely pushed hard into one side of the guide, I'd expect cracking or at the very least uneven wear.

Honestly, it looks like you've averted a total disaster - one valve head snapped off and it hits the fan very, very quickly.
I'm Going to pull the heads apart here in the next few days to see just how lucky I got
 

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Discussion Starter · #23 ·
I'd check all the push rods, doesn't Adv. a cam bring the exh. valves closer to the piston and Ret. the cam bring the int valves closer or is that the other way around?
I'm not sure, but my timing was locked out at 34 degrees. I looked at all the push rods they were in good shape with no deformation or bends. Only the cam lobes for those cylinders showed abnormal wear
 

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1968 Malibu sport coupe, 489 ci. 590 hp 600 tq, RV T-400 Freakshow 3200 stall, 3.73 12 bolt posi
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If your cam looks "Abnormal" I'd pull the cam and either flush the engine real good or pull it out like others have said but that's where it's open up the wallet time and your engine is down awhile, parts supply chain issues?
 

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I'm not sure, but my timing was locked out at 34 degrees. I looked at all the push rods they were in good shape with no deformation or bends. Only the cam lobes for those cylinders showed abnormal wear
Advancing the cam and advancing the ignition timing are two different things. Advancing the cam affects piston-to-valve clearance, advancing the timing does not.
 

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Discussion Starter · #26 ·
I did not throughly read what was said by shovelrick. That's what I get for responding before I had my morning coffee! Thank you for catching my misinterpretation
Advancing the cam and advancing the ignition timing are two different things. Advancing the cam affects piston-to-valve clearance, advancing the timing does not.
 

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Discussion Starter · #27 ·
motor is already out and on the stand. So I have no problem tearing it down. Cam was getting swapped along with new pushrods lifters and rockers. Might be more in the short block now. Here's a few shots of the affected lobes
If your cam looks "Abnormal" I'd pull the cam and either flush the engine real good or pull it out like others have said but that's where it's open up the wallet time and your engine is down awhile, parts supply chain issues?
 

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Just had a customer send a cam in and lifters that had some excessive wear on the roller lobes....Had 2000 miles on the engine....closing side of lobes have divits on the intake lobes....we believe he has P to V issues.
 

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I’d be going roller lifters. Seems only a couple companies make decent cores anymore for flat tappets. If I had to run a flat tappet I’d be looking into Motul classics oil.
 
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The culprit is the fact that you dont have enough clearance :) Probably was close before you decked the engine and now you pushed it over the edge. How much cylinder wall clearance do you have ? The pistons are probably walking around a little bit too.



When you did that how much clearance did you have atr the edges ? I like to see at least .050"



If the valves touched (which they obviously did) I would definitely have them pulled out and lightly refaced to be sure. You would be amazed at how a valve spring can pull a slightly bent valve closed.



Has the one head been milled more than the other ? Or the valve seats not cut in to the same depth ?

The pistons should be fine but I would pull all 8 and have them fly cut to give you enough room, especially if you are going with a larger cam. You need to be VERY careful having this done because it is very easy to cut into the top ring groove on those pistons.

Its all simple engine building 101 :) Check everything and then check it again.
Bill is right on. Everyone (or us non-pros) check P/V with clay measured on the flat of the valve relief but no one (except a pro) checks radial clearance. I ran into the same issue with set of GMPP ZZ502 heads (these have 2.25 intakes) , and it was worse, 7 bent valves and 1 lost valve it got beat so bad. Your pistons are Speed Pro Hypereutectic, they are only made for stock valve sizes. My block had to go from .030 to .070 to clean up the one cylinder.
 

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Discussion Starter · #32 · (Edited)
I found out the hard way, the valves won't clear after 0 deck. Haha
Worked fine when they were .025 in the hole though!🤦‍♂️
Agreed, I will check every cylinder for valve relief and radial clearance moving forward. I will hang these paper weight pistons in my shop as a reminder now.
Bill is right on. Everyone (or us non-pros) check P/V with clay measured on the flat of the valve relief but no one (except a pro) checks radial clearance. I ran into the same issue with set of GMPP ZZ502 heads (these have 2.25 intakes) , and it was worse, 7 bent valves and 1 lost valve it got beat so bad. Your pistons are Speed Pro Hypereutectic, they are only made for stock valve sizes. My block had to go from .030 to .070 to clean up the one cylinder.
 

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1968 Malibu sport coupe, 489 ci. 590 hp 600 tq, RV T-400 Freakshow 3200 stall, 3.73 12 bolt posi
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Those pistons are usable just fly cut the valve reliefs, either get a Good hyd flat tappet or a Good roller cam and Good lifters, if you go roller cam you'll want to watch Scott Foxwells Youtube vid about setting up valve train geometry, that's if you're using roller tip rockers.
 

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Discussion Starter · #35 ·
I am going with this roller and lifter setup.
Howard’s CL120605-12 and ultra pro mag rockers.

Those pistons are usable just fly cut the valve reliefs, either get a Good hyd flat tappet or a Good roller cam and Good lifters, if you go roller cam you'll want to watch Scott Foxwells Youtube vid about setting up valve train geometry, that's if you're using roller tip rockers.
 

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motor is already out and on the stand. So I have no problem tearing it down. Cam was getting swapped along with new pushrods lifters and rockers. Might be more in the short block now. Here's a few shots of the affected lobes
that is ugly;
full tear down and flush of block and wallet is indicated :(
 

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Bill is right on. Everyone (or us non-pros) check P/V with clay measured on the flat of the valve relief but no one (except a pro) checks radial clearance. I ran into the same issue with set of GMPP ZZ502 heads (these have 2.25 intakes) , and it was worse, 7 bent valves and 1 lost valve it got beat so bad. Your pistons are Speed Pro Hypereutectic, they are only made for stock valve sizes. My block had to go from .030 to .070 to clean up the one cylinder.
For the OP and others, just to be clear, yes most of us amateurs, (myself included) use the clay method, but radial clearance can still be checked with the clay method, (that's what I do). Radial meaning the distance between the valve circumference and the beginning inside edge of the valve relief, ( the "eyebrow"). Some sources claim that the absolute bare minimum is .030" of radial clearance, but .050" is better. And I'm pretty sure that some pistons will rock in the bore during engine operation more than others. So that's just one variable that needs to be accounted for when considering radial piston to valve clearance
 

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Look into checking clearances and running with a thicker head gasket. From the looks of the witness marks on the pistons, I agree that a complete tear down and inspection is in order.
 

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Discussion Starter · #39 ·
All the intake valves are bent on 2,4,6,8. No surprise there. The guides surprisingly still have good suction when pulling them out and capping the top of the guide. I'm not sure what degree of movement is acceptable while shaking the valves, however they are all very similar in wear in their group (ie. intake and exhaust)
I will disassemble the other head tomorrow and have something to compare this one against.
 

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1968 Malibu sport coupe, 489 ci. 590 hp 600 tq, RV T-400 Freakshow 3200 stall, 3.73 12 bolt posi
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You should measure the CC's of both your heads, my 1969 063 heads that had been milled ?? X's over 50+ yrs came in 98-99 CC's luckily the 2 heads stayed together as a pair all those yrs., 100.9 was factory on 215 heads, also watch your Squish/Quench area when reassembling, my small dish pistons were .018-.020 down and I was going to use Mr Gasket steel shims .020 but to keep P/V farther apart I used .027 MLS and got .045 -.047 but .039 - .040 is better from what I've read, No Pro Here :)
 
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