Camshaft 350 v8 5.7 - 1988 k1500 Scottdale

[Joshgrizzy24]

I am quite sure my camshaft is worn in my truck and needs replacement. I don't known the true mileage, but did check compression and had approximatelty 130 in each cyclinder and my book said a newer engine should have 150. If I replace the camshaft, lifters, and timing chains/gears then do I have to get my engine rebored and piston rings replaced? Is it worth changing or should I buy a crate engine or used engine? I got a 2 main bolt engine. I plan to use this truck to pull my boat and drive around once in a while...

 

[Hobie]

Heres the thing, if you want the full potential of the new camshaft, a rebuild on the engine wouldnt be a bad idea at all. Also, I'm not too sure if theres a big difference between the tbi blocks, the vortec blocks, but every vortec I've had had about 170-175 psi of compression. But I do think TBI's are lower compression. But anyways, you would definitely see a big difference if your camshaft is intact worn, and even if you put a higher performance camshaft in. But you shouldnt HAVE to rebuild the bottom end. Now, what you may run into, is if you decide to rebuild the top end, you should rebuild the bottom end as well, and vise versa

 

[Lanny]

If youre going to replace your lifters, I would pull one of the heads and check wear on the cylinder walls. If you have scoring or your cross hatch is gone, its time to rebuild.

 

[PlayingWithTBI]

Compression is a little low, does it burn oil or smoke when you start it up after sitting for a while? Yes, the TBI is lower compression than the Vortec. Either way the TBI peanut heads and cam are anemic at best. A Mr Goodwrench long block was put in my truck by the PO in 2002 just before I bought from him. A A little over a year ago it blew the head gaskets and started overheating. Since I've been running Mobil1 ever since it was installed and it didn't burn or leak any oil, I replaced the top end with aluminum heads and a stiffer flat tappet cam, as well as a lot of other stuff. It's still running fine, no leaks or burning of oil. The dip stick shows the same level after 5000 miles intervals.

Anyway, if/when the bottom end lets go I'll just buy a 383 short block and transfer the top end parts but will probably go with a roller cam this time.

 

[c1500deathtrap]

Why not check the tappet lift before tearing apart the top end? Unbolt a rocker arm, and measure the travel of the pushrod as you turn the motor over by hand (or power if you like). Across a standard 1.5 rocker the tappet lift should be a quarter inch or so. Dial indicators are preferred, but a fine ruler and a good eye may be good enough to tell if its really dickered.

 

[RichLo]

^ Yea. How did you diagnose that the cam was worn out?

Also with the compression, if you only pulled 1 spark plug at a time the compression can be significantly lower than if you pulled all 8... piston speed can greatly influence your results. And on that same note how old is your battery, starter and cables?

IMO, if you have 130psi +/- 5ish psi across all cylinders your engine is fine.

 

[Joshgrizzy24]

^ Yea. How did you diagnose that the cam was worn out?

Also with the compression, if you only pulled 1 spark plug at a time the compression can be significantly lower than if you pulled all 8... piston speed can greatly influence your results. And on that same note how old is your battery, starter and cables?

IMO, if you have 130psi +/- 5ish psi across all cylinders your engine is fine.

I only pulled one spark plug at a time.

When I got this truck it drove fine for about 10 hours back from ND. Then it had trouble starting randomly, but would crank? Once started the engine would run fine, but then the truck began to have more trouble starting and then the engine started to idle rough. Now the engine starts fine, but when I give it gas it stalls out. I cannot go above 10 miles per/hr and when I stop, it basically shakes, stalls, and eventually shuts off (Sometimes backfires). If I push the pedal to accelerate at a stop sign, it will stall out, but always starts up. This is a TBI engine

Parts I replaced so far:

front upper and lower ball joints, new front tie rods, new pitman arm, idler arm, stabilizer links
New front lug bolts
Front Differential fluid change
Oil Pump Replacement
Oil pan gasket replacement and oil pan bolt replacement
New filter and oil
Installed new driver Side Exhaust Manifold - I couldn't get old CO2 out, so I bought a new manifold
EGR Valve
Replaced O2 Sensor
Coolant Temperature Sensor
Replace spark plugs & tested wires were getting spark with tester
Replaced fuel pump - tested gas pressure
Replaced distributor cap and rotor and checked timing was at 0 degrees with a timing light
Replaced Throttle Position Sensor (TPS)
Idle Air Control valve
Rebuilt and cleaned Throttle body with rebuild kit
I can see the injectors spraying gas
Replaced fuel filter and ran fuel system cleaner through truck
Replaced front shocks
New front radio speakers
Rewired trailer harness and added harness bracket
Changed driver and passenger side front wheel bearing hubs
Replaced rear shocks
Replaced rear tail light circuit boards and rewired tail light harnesses.

I brought the truck in to have my exhaust welded back together and the mechanic who has been in town for about 60 years said there is no point in fixing the exhaust because the camshaft is bad...stated he could here it and feel it in the way it drove - said it is making a plopping noise. mechanic is an old timer and he said he doesn't do engine rebuilding any longer because he is to old. I tested compression and figured I could remove the camshaft and measure it and look at the top end as well. THE TBI is now covered in black and the last code I got was 45 Rich Exhaust. It does backfire out of exhaust, but half my exhaust is cut off...

 

[Hipster]

All plugs need to be out, throttles plates held open, and a fresh battery to get accurate compression test readings. You need max rpm via the starter motor. Signs of a cam going flat are backfiring out the intake or exhaust and noise, a rocker arm clattering etc. most times.

Foul the spark plugs ONE TIME and they can be no good. Change them out. Injectors need to cycle not just dump fuel. Dumping fuel is not an accurate indication of working properly.

There are a few others on this board much more versed in how the injection works and tests procedures so maybe they'll chime in. I wouldn't tear into the engine just yet.

 

[Joshgrizzy24]

Would an obd1 scanner be able to diagnose a bad cam shaft by the data that is output? I am willing to try anything...hah

 

[PlayingWithTBI]

Replaced Throttle Position Sensor (TPS)
Idle Air Control valve
Rebuilt and cleaned Throttle body with rebuild kit
I can see the injectors spraying gas

When you changed these did you calibrate them?
TBI tuning-website - Tuning the TBI.pdf

Take a timing light (preferred) or a flashlight and shine it behind the injectors. They should be spraying evenly with no drips. What kind of distributor do you have? When was the ICM last changed and was a high quality insulating paste used underneath it? When you checked the timing was the EST wire disconnected? You can advance the timing a few degrees to see if that helps, the ECM doesn't know the difference, it still thinks you're at 0BTDC.