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Bad cam?

P

procharlie

Well-Known Member
I have TTA #754 that doesn’t perform as well as it should. I can’t get it to rev past 4000 and it idles rough, etc. I started looking into it by removing the valve covers and mounting a depth gauge on top of the valve lifters that I could access easily. When I slowly rotated the crank manually I measured at most about .280” lift, and some were less than .200”. I did see some leakdown from the lifters but I can’t imagine they would leak .200” so I assume the cam is shot.
Can anyone tell me if my assumption is correct? If so, is it possible to remove/change a cam on the car without pulling the engine? I may just pull it anyway and check it out completely, but I have no reason right now to suspect the bottom end is not OK.
Thanks for any help you can provide.
 
If a cam lobe or lobes are wiped/worn I would pull the motor and clean it out as the metal shavings from the wiped lobe would have swam around the oil and may have damaged the bearings.

How is the oil pressure?

I believe it is possible to remove the front cover and pull the cam out with the motor in the car. The intake manifold must come off and the intercooler and rad may need to come out. With all that I would rather pull the engine and make it easier on your back (I don't like bending over the fender).
 
Thanks for the good info. You are right, it would be a lot easier to work with the engine out of the car, and it probably should be completely gone over/cleaned. I will start pulling it ASAP.
Charlie
 
I don't see why it shoudnt rev past 4000 even if the cam lobes are worn but that's my opinion,yes you could change the cam with the engine in the car just work intensive you would have to remove radiator,fans,intercooler, front accessories,timing chain cover,intake manifold etc.But if the car has a lot of miles I would do what Jaredsoon said and pull the motor.:eam:
 
First thing i would do is verify that FP is rising w/boost, then ask if it is the orig flat tappet cam and did you use ZDDP ?
 
never had zddp in my gn and its had a hard race life ... no whipped lobes though ... always used royal purple an not the thin mobil 1
 
Lotta good info here. I didn't build the engine so don't know what they used, but I'll try to check FP with boost. I have some ZDDP and will use it when I put it back together, along with assembly lube. I don't want to ruin a new cam if that's what it ends up needing.
Thanks everyone for the good comments.
 
procharlie said:
Lotta good info here. I didn't build the engine so don't know what they used, but I'll try to check FP with boost. I have some ZDDP and will use it when I put it back together, along with assembly lube. I don't want to ruin a new cam if that's what it ends up needing.
Thanks everyone for the good comments.
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if u put a new cam in put a roller in it ! well worth the money
 
Ok, I've never looked into a roller cam before but have read a lot about them in the forums, and I will surely consider it. I also wondered about roller lifters, if they really make much difference and are worth the extra expense for anything other than an all out race engine. The car I'm working on is my second TTA and I plan to sell it after I fix the engine and paint it, so I don't want to put any extra money into the car that I can't get back when I sell it.
 
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If you get a roller cam you should use a roller lifter as the cam lobes will not spin the lifter like a flat tap cam would. I would go roller everything or flat tap everything. Pick one.
 
procharlie said:
Ok, I've never looked into a roller cam before but have read a lot about them in the forums, and I will surely consider it. I also wondered about roller lifters, if they really make much difference and are worth the extra expense for anything other than an all out race engine. The car I'm working on is my second TTA and I plan to sell it after I fix the engine and paint it, so I don't want to put any extra money into the car that I can't get back when I sell it.
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If your going to sell it, it's a no-brainer... flat-tappet.
 
I re-read my last comment and realized what a dumb thing I said. I meant to ask if roller rockers were worth getting in addition to a roller cam. I know a roller cam is made to work with roller lifters - duh - but I don't know how much you gain from roller rockers, and would I need to replace the pushrods if I got them?
I will stick with the flat tappets for the car I'm working on now, but this would be good info for me for future builds. I have a '56 Chevy Bel Air I am restoring and might put a new motor in it, and hope to eventually (on my bucket list :wheelchair:) build up a kit car with a Buick 3.8 turbo engine - I have most of the parts for one that I obtained during my past TTA, GN, and T-Type efforts.
 
I pulled the engine and made more accurate cam lift measurements. The intakes are all .240" to .247" and exhaust are .255" to .263" (that's valve lift of intake .372 to .383 and exhaust .395 to .409). I have looked online for specs and these sound like close to stock, and the cam doesn't show any signs of unusual wear.
Does this sound like a good enough cam to leave in, considering I will be selling the car?
BTW, I did try to check if FP increased with boost, and could read the gauge that has been mounted on the fuel rail. It increased when the car was in Park and I manually opened the throttle to reduce vacuum, but couldn't build up boost without having the car in gear, which I couldn't do by myself, so I don't know if it would have gone up any more at high boost - but I have no reason to think it wouldn't.
 
procharlie said:
I pulled the engine and made more accurate cam lift measurements. The intakes are all .240" to .247" and exhaust are .255" to .263" (that's valve lift of intake .372 to .383 and exhaust .395 to .409). I have looked online for specs and these sound like close to stock, and the cam doesn't show any signs of unusual wear.
Does this sound like a good enough cam to leave in, considering I will be selling the car?
BTW, I did try to check if FP increased with boost, and could read the gauge that has been mounted on the fuel rail. It increased when the car was in Park and I manually opened the throttle to reduce vacuum, but couldn't build up boost without having the car in gear, which I couldn't do by myself, so I don't know if it would have gone up any more at high boost - but I have no reason to think it wouldn't.
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You can have every reason in the world to think that it don't rise 1:1 until you see it with your own eye's, very important with these car's and ALOT of bad things can happen if it don't... hard to find free good advice...
 
Thanks for the good free advice :thumbup:, I'll check it out when I get the engine back in. First, I just have to decide if I will leave this cam in - I would appreciate any comments based on my measurements of the lobe lifts.
I am also thinking about blocking off the EGR in the process of re-assembly; it sounds like a good thing to do, and I have no inspection problems to worry about here in Alabama. I'll check into chips that account for it being out of the system if necessary, but I think if I leave in the solenoid/switch it won't give me an error signal. Any helpful hints about how to do this correctly? I'll also be searching the other forums for any additional info.
 
Update: I blocked off the EGR and put the engine back in and drove the car. It still didn't run any better than before, and soon started to spew oil all over the exhaust piping - smoke came out everywhere! - so I pulled it back in my garage and looked it over. I didn't see anything obvious and since the oil was apparently coming out by the back of the engine I thought it was the rear main seal, so I pulled the engine again. I found it was actually the oil pan gasket that was leaking at the rear end. I had used a rubber gasket and that was apparently a big mistake; I'll use a better one next time. So now I have to figure out if I should just replace the gasket and put it back in or consider also replacing the cam since it's out.
I'm asking if anyone can give me any advice/comments as to whether I should replace the cam based on the measurements I made - see my earlier post - or is it good enough to leave in considering I will be selling the car. I will check on FP after it is back in and running again, to see if that's my problem, and I don't want to have to open up the whole engine to put in a cam if it probably will not make much/any difference in performance. I'm sure there are a number of you who have much more experience than I with this engine who could provide some good guidance.
Thanks in advance for your help.
 
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The turbotweek chip disables the EGR, if you have stock heads go back with a stock cam, these engs. are real simple... untill you start modifiying... then watch out for the snake in the woodpile..
 
Sounds like the cam is ok. At 4000 rpm does it nose over like it ran out of fuel? Sounds like fuel problem. Fuel pump may put out pressure but not enough volume. Best way to check is watch fuel pressure while driving and see if it drops. Could have a plugged fuel filter or weak fuel pump.
 
as far as the rpm only goes to 4 thousand rpm what is actually doing is it breaking up after that,it could be a ignition problem or a fuel problem,about the rough idle turbo tweek makes a emission chip that it eliminates the EGR and it would idle much better.About the oil pan gascket you might of over torque it,the cork gasket I think is a better one that's my opinion.To check the fuel pressure if it is rising 1 to 1 you would need to have some type of gauge taped to the windshield or a hood mounted gauge installed,
 
thanks for the great comments. I used some gasket tack spray on the rubber gasket, but that apparently wasn't good enough to hold it in place. I have a cork gasket I will use this time.
I will leave the cam in based on your inputs. It does sound like it's maybe not getting enough gas, and I didn't think about the fuel filter. I'll replace that and see if there is a way for me to monitor fuel pressure while driving. I hope it's something like that, as it's an easy fix that doesn't require any real engine work. I'll let you know how it turns out. :thumbup:
 
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