Team Camaro Tech banner

1 - 15 of 15 Posts

·
Registered
Joined
·
8,097 Posts
Discussion Starter #1
Panic has nearly set in . . . I just swapped cams in my 383. Went from a Comp Cams 275 DEH to a Comp Cams 282s mechanical. I followed break in procedures running the engine 1500 - 2000 RPM for 20 minutes, no problems. I drove the car easy for about 30 miles rechecked valve lash and changed the oil. Then out for a drive again and got on it a little, noticed a real lack of power at all RPM's when past 1/2 throttle. No one cylinder missing just a general lack of power.

Starting troubleshooting the lack of power problem and borrowed a friends 650 DP carburator. Put it on and started it up. Started backing out the driveway and heard a random banging sound. Pulled back in the drive and popped the hood. Sounded like it was coming from the back of the engine down low. The noise became more regular so I shut it off.

I popped the valve covers. Cycled the engine and everything looked good. Valve lash still at .022" on all eight. Pulled the plugs and noticed the electrode on my number 8 plug was bent up.

Any ideas? I'm in denial that anything could possibly have got down the intake when I changed the carb, I accounted for every single nut, bolt and washer.

Please help before I go jump off a bridge somewhere!!!! What should my next step be (after they talk me off that bridge
)? Compression check or should I just pull the head?


Thanks

[This message has been edited by Eric68 (edited 06-30-2001).]
 

·
Registered
Joined
·
27 Posts
#8 is a headache to get in sometimes, you sure you didn't hit it on something putting it back in? Or did you even have it out during this whole process? I'd try another spark plug, gapped correctly and see what happens.
 

·
Registered
Joined
·
3,692 Posts
It definately sounds like something got dropped in the cylinder. I would try another plug also and see if there is any difference. Is the oil pressure still good? Does the idle still sound "even" (no noticeable miss)? You said that all of the valves lash was still in spec, but what about a broken valve spring? I know you said that the electrode was bent, but maybe (hopefully) it is unrelated. How much idle vaccuum? Cranking compression? Other than the duration and the fact that this is a solid lifter cam, there isnt much difference in valve lift by the time you figure in the lash settings, so that shouldnt have caused any problems, but you never know. Let us know what you find.
By the way, how does the idle sound with the 282s compared to the 275DEH? Just curious.

------------------
375hp 78 Chevy truck
77 Chevy Nova
95 Chevy Lumina 3.4L
and building a 78 Nova
 

·
Moderator
Joined
·
10,142 Posts
Sounds like something got in there.
Pull the exhaust manifold/header and crank it around until the exhaust valve is open and the piston is coming up and shine an inspection light in through the spark plug hole, then look through the exhaust valve opening into the cylinder.
A borescope would be nice!

Take a good look at your valve springs and keepers.
A spring can break near the end and not be noticed, can cause the valve to float, hit the piston.
Good luck, David

------------------
Check my web page for First Gen Camaro suspension info:
David's Motorsports page
First Gen Suspension Page
67 RS 327
69 Camaro Vintage Racer
65 Lola T-70 Chev 350 Can-Am Vintage Racer
 

·
Registered
Joined
·
8,097 Posts
Discussion Starter #5
Thanks for the quick replies. The car idled well (actually better than with the other cam). It was idling evenly with no noticable miss. But I did not run it long after I started hearing the noise, the noise was pretty loud.

Oil pressure was good - steady 50 psi at idle.

After closer examination of the damaged plug from number 8 I noticed the porcelain insulator is broken and the whole insulator slides up and down on the electrode. Could the cylinder have been dead and firing in the exhaust? You think I would have noticed a miss though.

I cycled the engine with a remote starter switch while the plug was out to see if I could hear anything rattling around in there - nothing. It sounds perfect when just cranking. I also put the cylinder close to TDC and fished around with a piece of electrical wire through the spark plug hole, could not seem to find anything inside the cylinder.

I don't have a compression gauge handy, but the cylinder seems to have good compression when I cycle it with my thumb over the plug hole. At least similar to the others.

I'll try putting a new plug in #8 and my original carb back on and see if it still bangs. Then off comes the header and I'll look in the exhaust port with a flashlight.

My gut feeling tells me something is wrong in the bottom end though - conn rod coming loose and smacked the plug maybe? I hope not, all top notch components down there (KB pistons, Eagle 5.7" SIR rods, Eagle cast crank, ARP bolts, studded 4 bolt main).
 

·
Registered
Joined
·
8,097 Posts
Discussion Starter #6
BTW I checked for valve spring bind during my cam installation. Checked OK. The springs were installed on the heads from Summit. They are 115# (at installed height) 1.25" springs rated for .520" max lift. The 282s cam requires 110# springs and lift is .495 (minus .022" lash = .473" nominal lift?). I figured a slightly used 115# spring would be right in the ball park.

Looked closely at the springs on #8 nothing appears to be broken.
 

·
Moderator
Joined
·
19,748 Posts
Eric,
hate to be a pessimist but you don't think the piston found a valve do you? i hope not.does sound like somethings wrong,broken plugs just don't happen for no reason. good luck.

------------------
My '68 Camaro
Doug G.
68 Camaro
406 ci.
[email protected] W/ 2.73POSI.
 

·
Registered
Joined
·
8,097 Posts
Discussion Starter #8
Update - put my carb back on, new plugs and fired it up. The banging is GONE! I did a compression check and checked all the valves again. Everything seems OK.

cyl 1=205#
cyl 3=204#
cyl 5=203#
cyl 7=205#
cyl 2=205#
cyl 4=202#
cyl 6=203#
cyl 8=200#

I did notice that the new NGK plugs I put in have a slightly longer reach than the Accel's I had - about 1/32". You don't think I could have slapped a plug with a piston do you? The KB pistons I'm using have a 12cc dish - should be tons of room unless the plugs are not located in the dish part.

Went for a test drive. The motor ran great when I drove it easy. After about 60 miles and I was sure nothing was wrong in the bottom end, I punched it and there's still no power above 3500 RPM.

I swapped carbs - no change. Swapped coils no change. Fuel pressure is steady 6-7 psi at all rpms.

Any ideas?

[This message has been edited by Eric68 (edited 07-01-2001).]
 

·
Registered
Joined
·
3,692 Posts
You didnt install the cam advanced, did you? That cam already has 4 degrees advance ground in. That is a LOT of cranking compression...you could easily get away with more cam. How do your plugs look after a hard run? That extra duration may require more jet in the carb...meaning that you may be running on the lean side now. Just a thought.

------------------
375hp 78 Chevy truck
77 Chevy Nova
95 Chevy Lumina 3.4L
and building a 78 Nova
 

·
Registered
Joined
·
8,097 Posts
Discussion Starter #10
I installed the cam straight up (not compensating for the 4* advance / 106 lca ground in). I did not degree it though, just lined up the dots. Do you think that 4* either way would make that big a difference in power up top? I'm missing like 100 horsepower easy.

I'm starting to wonder about valve springs, maybe I'm getting valve float. With the dished piston and lots of valve clearance maybe I'm not hearing it. It's tough to hear much with my exhaust anyway. I may just replace the springs to eliminate the possibility, especially after the banging sound problem.

Plugs looked on the lean side so I jetted way up and ran again, no difference. Started with #68 pri, #74 secondary. Changed to #72 PRI, #76 SEC. Plugs looked too rich and no difference in performance.
 

·
Premium Member
Joined
·
4,817 Posts
By any chance do you have a vacuum secondary carb that isn't opening with the new cam? Also, I once had a piece of junk fall into a cylinder and got it out by starting the car with that plug out. With the compression, it blew it right out!

------------------
Rick Dorion
69 RS Conv,355,M20,4.10's
 

·
Registered
Joined
·
8,097 Posts
Discussion Starter #12
Rick - I swapped in a double pumper to test and there was no change. I initially thought that might be the problem because the car acts like its running on a dinky two barrel. But even with the DP it dogs out big time.

Comp Cams tech line thinks I should test valve spring pressure and play with the ignition timing. I let you guys know how it goes.
 

·
Registered
Joined
·
8,097 Posts
Discussion Starter #13
It's fixed! The lack of power was a bad distributor. Accell billetproof - 3 months old. Counterweights were sticking. When I set the initial timing at idle full mechanical advance was in so my timing was 12 degrees retarded from normal.

The banging is gone, I'll tear it apart this winter and see if there are any signs of something getting sucked through cylinder # 8.

Thanks again guys, good advice = great site.
 

·
Registered
Joined
·
3,692 Posts
I swear man, you seem to have the baddest luck. Glad you figured it out. So, how does it run now?

------------------
375hp 78 Chevy truck
77 Chevy Nova
95 Chevy Lumina 3.4L
and building a 78 Nova
 

·
Registered
Joined
·
8,097 Posts
Discussion Starter #15
How does the saying go . . . if it weren't for bad luck I'd have no luck at all. Actually, I considered myself pretty lucky that I didn't break a piston or something real bad. After thinking about it a bit, I did drop a plug (either #6 or #8) when I changed them a week or two before the cam project - maybe I cracked the insulator and the problem occured when it came completely loose. This was definately the weirdest problem I've ever seen.

But I'm real happy with the way it runs now. Torque and low end power is just a tad off from where it was, but it pulls much harder from 5,000 to 6,000 RPM. What little low end I'm missing may come back when I get rid of this borrowed stock HEI distributor. A little steeper advance curve will probably do the trick.
 
1 - 15 of 15 Posts
Top