Flat cam

[bobalob]

on the way to work last week i suddenly lost about 50% power and oil pressure so i brang to shop after work and they replaced oil with 20-50 and got good pressure but said cam was flat and would be 700 for new 268 cam and lifters installed. Unfortunately i am poor so i bought cam+lifters, gaskets, tools and began disassembly. So far it has gone good and interesting seeing the guts of that thingy that makes me go. Now I have cam and lifters out(completely wiped out) and am ready to start reassembly,given that i have no experience what so ever any tips, tricks, instructions, cautions would be greatly appreciated. It is a 350 carbed motor with only about 5000 miles on it!

 

[tRustyK5]

One thing that threw me a curve a few times was the timing chain installation. The books I have all show the dots lined up so the cam gear dot is at 6 o'clock and the crank gear dot is at 12 o'clock. This makes line up idiot proof, so that method is good that way...but the motor is then at #6 TDC not #1.

So, what would usually happen to me is I'd drop the distributor in thinking I was on #1 and the damn thing wouldn't start. Then I'd eventually figure out the distributor was out 180 degrees.

What I'd do is get the timing chain on as shown in the book, then rotate the engine until both dots are at 12 o'clock and button it up. Then when you drop in the distributor it will actually be correct the first time and should fire up without any trouble.

Don't forget the cam break in...usually 2000-2500 rpm for 30 minutes or so. I'd highly recomend a big box fan in front of the rad and to triple check all fluids and bolts before firing it up. Lastly don't forget to use plenty of assembly lube.

Rene

 

[88-383]

Bob

What cam was installed that wiped a lobe? It's pretty unusal for this to happen, unless you've got high spring pressure or very agressive lobes. A 268 can't really be considered agressive IMO.

Another thing to worry about is coil bind. What kind of lift was the bad cam producing? Do you have stock heads? The 20/50 trick also has me a little nervous.

So the shop said you wiped a lobe and that caused oil pressure loss? Or did you loose oil pressure then wipe a lobe? I'd move real slow and try to get to the bottom of what went wrong, before I start throwing new parts at it.

KM

 

[Mad-Dog]

Soak the lifters in motor oil before installing, use the supplied assy lube and coat the cam lobes, slip er together then align the dots on the gears and install them onto the cam and crank together.
Reassemble the rest of the motor with the correct intake gaskets and rotate the crankshaft 1 complete revolution.....
now the distributor is ready to drop back in at the #1 wire position.
The crank rotates at a 2:1 ratio with the cam because the cam gear is 2x the size of the crank gear.....TRIVIA

If you did not drop the pan then you will be able to reuse the timing cover lip seal by applying a dab of sealant to it then forcing the timing cover down onto the pan and back over the guide pins in the front of the block........

Hope this helps

 

[southernspeed]

Bob

What cam was installed that wiped a lobe? It's pretty unusal for this to happen, unless you've got high spring pressure or very agressive lobes. A 268 can't really be considered agressive IMO.

Another thing to worry about is coil bind. What kind of lift was the bad cam producing? Do you have stock heads? The 20/50 trick also has me a little nervous.

So the shop said you wiped a lobe and that caused oil pressure loss? Or did you loose oil pressure then wipe a lobe? I'd move real slow and try to get to the bottom of what went wrong, before I start throwing new parts at it.

KM

Wise words! The last thing you want is to wreck a new cam because you didn't find out why the last one got trashed! 5000 miles for a lobe can only be poor oiling, bad cam break-in or coil bind.

 

[bobalob]

Previous cam was also 268 and at about 1000 miles low oil level caused pressure drop(being totally unexperienced i guess i thought motor would tell me when it was thirsty like my beemer does, i was kind of hoping i wouldn't have to admit to this failure of mental acuity) shop said cam was partially affected then and a piece of metal along with really dirty oil caused pressure loss this time and finished off the cam and actually about 5 lobes and lifters were wasted. Also with 20-50 I am about 8 or9 psi over my usual oil pressure and i was going to drain and replace along with possibly oil pump and i would check main bearings but anymore $$ and i will be forced to junk it anyways.

 

[southernspeed]

I've been away for a week, how did you get on with the motor rebuild? I use 5w30 in both my trucks and really like it. Did you break the cam in properly (if you have it running yet)?

 

[bobalob]

rebuild went good until compression problem arose but it was my first time adjusting valves so my concept of zero valve lash was a little out of sync with reality . But as soon as that problem was rectified it started right up and i did 20 min at 2000 rpm. Sounds and feels great but I haven't had time to drive it yet or the gas money. I was also wondering lf i should replace the oil and filter after a short run and go back to 10-30w?

 

[southernspeed]

Just replied to your other post then worked out which order you posted them in!
I run 5w30 in mine. 10w30 would do fine. 20/50 is for old motors IMO.