interrupted cam break-in

Grumpy

The Grumpy Grease Monkey mechanical engineer.
Staff member
Good day...well I've got my LM1 350 complete rebuilt. New cam installed and everything check, double checked and triple checked in terms of setting valve lash, etc. Heads are rebuilt with full valve job, new springs and so on.

Got the engine on the TDC #1 compression stroke, got the distributor in, fired it up and it sounded like hell, like a misfire. Because its a flat tappet cam I put it up to 2000 RPM for the break in right away anyway, for about 2 minutes but the engine wasn't smoothing out so I shut it down. (Yes, I know you want to avoid doing that on a cam break in). I checked everything over (again), all looked good. Tried to restart it and got a massive (and I mean like a shot gun) BANG out the carb. So that's it, not cranking it again until I've found the problem.

The distributor is not 180 degrees out, if it was it wouldn't have run at all. I checked all the pushrods by rolling them between my fingers, none seem bent. I checked all the plug wire connections, and double checked the firing order on the cap, all is well. The only thing I can see is maybe the distributor was advanced too far on that inital start up, I didn't have it running long enough to be able to get a timing reading as I as immediately trying to find the misfire. The short time is was running, advancing or retarding the distributor seemed unresponsive.

So - if the distributer was somehow far too advanced to begin with do you get into an area where it will run like its missing, backfire out the carb and be far enough out that small changes by hand while running do nothing?

(Honestly the bang was so loud, I'm a little freaked out that its something else more internal being 100% brand new everything).


I did not see you mention checking all the valve train geometry,
and valve train clearances and the piston to valve clearances
,like spring bind, retainer to valve seal,
push rod to cylinder head slot,or guide plate,or rocker slot,too rocker stud,etc
.
nor that you degreed in the cam,
nor did I see the valves properly adjusted in the list?
do you have good oil pressure?
you may want to pull the plugs and verify the ground electrodes are not bent?

I.d for sure back off the rockers and verify the valve adjustment was done correctly
yes I know you think it was... verify it carefully
I start checking clearances and if those check out,
Id do a compression check,
verify the firing order, and plug wire connections,
and check the ignition timing, advance curve,verify TDC
Id reset the valves adjustment very carefully
http://www.acdelco.com/auto-parts/v...engine-oil-supplement-assembly-lubricant.html
eos.png


yes several hours reading in the links and sub links below, and don,t ignore the links,
but you may find that you know 90% of the info but that new 10% you ignore or forgot,

can get VERY expensive...
readings much faster and cheaper that parts replacing


http://garage.grumpysperformance.co...ectly-and-get-it-to-last-cam-install-info.90/

http://garage.grumpysperformance.com/index.php?threads/valve-train-clearances-and-problems.528/

http://garage.grumpysperformance.co...e-springs-and-setting-up-the-valve-train.181/

http://garage.grumpysperformance.com/index.php?threads/correctly-adjusting-valves.196/

http://garage.grumpysperformance.com/index.php?threads/valve-spring-installation-questions.12833/

http://garage.grumpysperformance.co...op-dead-center-1-for-timing-ignition-cam.966/

http://garage.grumpysperformance.com/index.php?threads/stock-gm-push-rod-length.3844/

http://garage.grumpysperformance.co...hanics-of-adv-ret-a-camshaft.4532/#post-12045

http://garage.grumpysperformance.co...ear-articles-you-need-to-read.282/#post-52473

http://garage.grumpysperformance.co...ing-down-a-valve-train-noise.6237/#post-32472

http://garage.grumpysperformance.co...swap-in-1-6-1-ratio-rockers.10671/#post-46039

http://garage.grumpysperformance.co...o-rockers-and-the-pushrods-rub.198/#post-3033

http://garage.grumpysperformance.com/index.php?threads/verifying-your-real-advance-curve.4683/
 
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Well a few interesting things...so I reset the lash by backing off all the valves and waiting a while to let the lifters "relax" then I did the EO/IC method on all of them. I actually did both vertical movement and rotated between by fingers (just cause that's the way I learned it years ago, if you just rely on twisting you can get "false positives" as the wrench socket shifts the rocker where it sits on the pushrod). It seemed that the moment I could no longer detect verticle movement you would start to feel twist resistence also. Put them one-half turn past that. I noticed that after this I can still wiggle the rockers side to side just a little by hand (these are factory stamped steel 1.5 rockers, and new by the way along with the studs they're on) and you can still rotate the pushrods if you really grip them with your fingers but its hard. Now after shutting it down with the backfires I noticed that I could rotate the pushrods more freely, and they all seemed to be at about 3 threads down the studs consistently. Tonight, they all wound up at 4 threads down. First time they were set to zero lash "dry" per comp cams instructions, this time they've been pressurized by the 10 minute priming and then the short time it ran.

I also took the cap off the rotor and pulled a few wires off (the distributor is the origial points type BTW - this car is a 1969 time capsule and the goal is to keep it that way even though far better technology is available) and the #8 wire came out of the disty without the crimped on contact and part of the insulation gone (cut by the crimping). That certainly could have accounted for the misfire when it did intially start up. Those were new Delco "premium" wires.

So tomorrow I'll pick up new wires again since I can't buy individuals and a new cap and rotor for the hell of it - they're cheap. Last thing I will do is use this long narrow turkey-baster type device I have to place more cam lube on the cam through the drain holes in the head (which are directly over top of the drain holes down to the cam). I can't hit every lobe that way but I'll do my best.

Totally understood about having someone around for the fire up. I would agree with that but I haven't got buddies in town that know anything about this - all those folks are still back in my home town, two hours away. But I do have the timing light ready, along with a temporary oil pressure guage (car doesn't have one but I plugged one it the oil sender hole) and a vacuum gauge along with a laser thermometer to keep an eye on temp. The manual choke puts the engine to 2000 RPM right away anyway, so if it runs right it will go there and stay there on its own while I check timing and the other bits. Being a manual choke it won't come off fast idle until I take it off no matter if its warmed up or not.
here's my update!

Starter - had it rebuilt by a shop, still cranked like hell. The battery is only 2 years old, and was fully charged, so I overlooked it but ruling out other things I checked - it was pooched. Warranty replacement and now it cranks like a champ.

Firing - With ram's horns manifolds the #1 and #3 leads run under the motor mount and are routed via clips attached to the oil pan. I wired it so #1 was the bottom wire in the clip and #3 was the top. At the wire loom at the back #1 was in the first slot closest to the motor, then #3 and so on. So this made it easy to identify which wire is which when hooking up to the disty. So you would think. I had marked each lead with its number and didn't realize that somewhere along the way (probably while bolting on the block mounts) I got the #1 wire on top of the #3 behind there. Meaning what I thought was #1 was #3 and vice versa. As someone said, it's always the simple things.

Starting - I cranked it, no backfires, no spitting but it would semi-ignite but not enough to overcome the starter. Made small changes in the timing and it fired up.

Brought it to 2000 RPM to continue the cam break in. The timing light said I had about 33 degrees advanced with the vacuum hooked up, but thats not really the right way to tell timing. Nonetheless I ran it for the next 10 minutes at 2000 RPM and then varied from 2000 to 2500 and back for the next 20 minutes. Burped the cooling system at the same time. 180 degree thermistat, block got to about 202 and intake housing got to 210 at its hottest before it burbed.

Shut it down, changed the oil.

Cranked it over with the started and the coil unhooked (after marking each pushrod) to see how badly I had botched the cam. Every pushrod was rotating except 3, all on the passenger side. But those three valves were giving the right amount of lift...so....?

The real test - checked the oil. I cut open the filter, could not find any metal in it at all. Got a clean rare earth magnet and ran it up and down every single pleat, it picked up nothing. The oil was the same. May have been a little bit of fine metal in it, but not enough to get on a magnet and not enough to see (I had to pour out some on white card and shine a flashlight on it to see what could be some very very fine particales). It could be additive also, or lube.

So...I think my cam is ok, time will tell. Next went to fire it up again to warm it up and tune the carb and set timing properly, and it wouldn't start. Ha! I swear its like it suddenly is too lean. But its got lots of spark, lots of air (checked the choke and butterfly specs/settings) and the accel pump and idle jets are doing their job also. So either too lean, or timing, or both
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Id suggest you keep an eye on that lifter that is not spinning fast, theres a chance the overly tight rocker caused damage that may get worse over time, youll know by the time you put an additional 20-30 hours running time on the engine if not sooner
lifter1jpg.jpg



http://garage.grumpysperformance.com/index.php?threads/cam-wear-articles-you-need-to-read.282/

http://garage.grumpysperformance.com/index.php?threads/rocker-push-rod-wear-issues.9815/#post-54088

http://garage.grumpysperformance.com/index.php?threads/valve-train-clearances-and-problems.528/

http://garage.grumpysperformance.co...n-clearance-for-new-383-sbc-cam-instal.13109/

http://garage.grumpysperformance.com/index.php?threads/magnets.120/#post-49772
 
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I REALLY hate to say this, but if the pushrod is not rotating, then the lifter is not rotating.
That spells DEATH for that camshaft. If you have not done so already, use some solvent to
clean the oil off of the top 2 inches of the pushrod and I use a paint marker to draw a line
along it's length. Then run the engine with a cutout valve cover to watch for rotation.
You also need to look for the proper amount of oil coming out of the ends of the pushrods
for lubricating the rockers.
Get some SMCo magnets inside that engine. If those lifters become a lathe to that camshaft,
you will circulate very hard and sharp shrapnel throughout the entire engine - destroying
EVERYTHING. Read here about what I went through:
http://garage.grumpysperformance.co...help-i-might-have-no-oil-to-the-rockers.3397/
http://garage.grumpysperformance.co...e-parts-dont-come-in-plain-white-boxes.11940/
3 lifter bases.png almost ready to fire.jpg DR top cutout vc.jpg drain plug.png lines on pushrods.jpg pools 1.jpg reflection.jpg #3 oil at idle.jpg #6 In SHOT.png 2 Delphi.png
 
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