Technical Changing Cam on a stock SBC 350

Hi All,

I have an open thread already regarding upgrading from my rochester 2 barrel or rebuilding it and running with it (I opted to rebuild it per many suggestions).

My C-10 has a 1975 engine in it and a 1969 rochester 2 barrel. I've described it as a tired engine but maybe that wasn't warranted and I don't have a clue what a tired engine really is. At times I feel I could use a little more power going up a steep hill but maybe its not too bad. I drive this around San Diego short distances for errands or take my paddleboard/rowboat out to Mission Bay or to a local surf spot and not on highways ever (too stressful with how people drive in CA!).

Someone (Chevy Pope) suggested I change the timing set. I measured 8-10 degrees slack watching the rotor turn and looking at timing mark. It's unknown whether the timing set was changed ever or if it has nylon gears in which case its a ticking time bomb. Since I have no way of knowing and there is some slack, I ordered a cloyes double chain timing set, oil pan gasket, timing cover gasket, harmonic balancer, balancer bolt, woodruff key.

One thing I wonder is if I should change the cam while I'm doing all this work. Would it be worth it if I don't change the heads, keep the ram head exhaust manifolds, and keep the 2 barrel rochester carb? The neighbor across the street (total typical suburban man-child) makes my blood boil with his harley davison noise machine and thats why I put glasspacks on my truck to rev it a little as I'm backing close to his driveway and piss him off sometimes and also why I love pulling out my chopped 50 shoebox and putting his ass in check. Would there be any reason to change my cam if I'm not doing much else besides a timing set? Although the lopey sound of a mild cam is awesome, I feel I can rev the motor a little with glasspacks and get a good enough bark when I want to be heard.

I'm not sure the history of this engine, and don't know if it was ever rebuilt, so I had low expectations on compression readings... but here's what I measured with the engine mostly cooled down/warm. I drove it around the block twice and pulled in the garage and pulled plugs out:

Readings in PSI taken 3 times for each cylinder with carb at WOT
Cylinder 1: 120, 120, 120
Cylinder 2: 123, 120, 120
Cylinder 3: 120, 120, 120
Cylinder 4: 120, 120, 120
Cylinder 5: 120, 120, 120
Cylinder 6: 117, 113, 113
Cylinder 7: 115, 117, 119
Cylinder 8: 120, 120, 120

The plugs looked really great. I had changed them out last summer after replacing the valve seals.. #3 or #7 would get drenched in black oil... now they are clean!

Do the numbers above look typical of a stock smog era 350 engine, and is my cam likely fine?

 

Good chance if the timing set it work out that the cams gone a little flat too and would explain it being a little bit of a dog. I’d change the cam while you have it apart.

 

It would be a bit more work to change the cam and I'm short on time and wanted to avoid changing it if its just for a lopey sound which some people really desire.

Its not a total dog.... except a little bit going up a steepish hill... I wonder if thats more because I have a 75 smog era engine rated at 140 hp or something anemic! I read online "The most anemic 1975 350 was rated at 140 hp with a two-barrel carburetor".

 

I wouldn't change the cam until you decide to pull the engine out and go through it. I wouldn't bother with the timing chain, either.

 

The smog era stuff are still quite a torquey engine. If it’s not great going up hill I’d say it’s going to be something basic like timing, carb tuning, mech/vac advance, vac leak etc. If you’ve not checked the ignition timing etc I wouldn’t bother with anything until youve given it a basic tune.

 

Those compression numbers are pretty close together,,,,,might be a little low but you won’t change that without a rebuild .
For an old smog engine it seems fairly solid.
I’m with Jim,,,,,wait until you go through it .
Besides,,,,,you pretty well explained your situation right now,,,,,no reason to rush if you don’t have time and can’t afford to do it at this moment.

Tommy

 

Precisely what I was thinking. I don't want to put much money in this engine or truck... I drive maybe 150 miles a year total.... I was going to leave it be until Chevy Pope mentioned in another thread he thinks I have a ticking time bomb with the nylon gears if its still stock... and I don't know the history of this engine... I ordered a timing set not knowing.. and by the time I take the timing cover off I would rather have the parts in hand if they are indeed nylon.

Do you think I should still check if it has nylon gears?

 

I have it tuned correctly.. timing is set correct, no vacuum.. I get 18 in HG of vacuum at idle. I haven't driven it uphill since rebuilding the rochester carb but maybe that will help. It felt rather torquey this morning when I drove around the block.. Again 140 hp on a heavy car uphill... I suppose it will feel a little sluggish no? Then again I have a tendency to really baby the pedal to keep rpms lower so maybe I just need to stop driving like a damn grandma and push the pedal harder uphill to get a better assessment.

 

I would look for clues that the timing cover has been removed. Kind of hard to explain, but I can usually tell by looking if an engine has been worked on before, or if it's a cherry. Hint: 50 year old cherries are very rare!

 

Thanks! I have the money for sure to rebuild the motor it just seems pointless because the truck has so much rust and I don't plan to do anything about it. I painted it by hand with a foam brush and many people compliment the truck and say they love it without knowing all the real rust underneath... its just to throw my surfboards in and drive short distance on a nice sunny day and enjoy the glasspack exhaust tone....

My only concern is the chance I have a ticking time bomb with the nylon gears that were stock to this motor.. I have no idea if the timing set was changed out. I prefer to leave the cam if possible for now thinking about this a bit more since I'm limited on time and don't want to pull valve covers, intake manifold, radiator and possible the front grill.

 

My only clue would be racing stickers on the back window (which I removed a long time ago)... shitty rebuild job on the Rochester carb (assuming it was the previous guy), and a lot of other hacked up things... other than that I may look again around the timing cover again.. I was hoping to see hints of the bright blue fel-pro type gaskets but just saw a bunch of grime around there...

 

What if the previous person removed the timing cover, looked at the nylon gears and said they are fine.... that could have been a while ago and its obvious now that the nylon gears can wear just from age and repeated heating/cooling cycles even if not many miles are put on them. I barely drive this thing but read with the nylon gears its the age that matters more.

 

I haven't seen the old style timing sprocket in an SBC for a very long time....

Take some pictures.

One clue that takes some work to see is the damper, where the lower pulley bolts to it. Very rare to see one without hammer marks, which indicate someone has been in there already.

 

Presumably you’re comparing it to your shoebox, what engine is in that?

 

If I had some concerns of an engine running, then found out I had 8 degrees of slack in the timing chain, I wouldn’t worry about a cam swap, I’d focus on changing the timing set, regardless of what it’s made of.

 

SBC 350 as well in the shoebox but it was rebuilt when the previous owner had it (supposedly) and has headers, etc.. however I've barely driven that car so I don't compare the two (at least not yet).

 

Thats what I'm thinking now, change the timing set and not worry about the cam.. the engine runs fine overall...

 

A cheap set of dump tubes, exiting before the bed will take care of the neighbor

 

Here is a photo dump... I don't see anything that makes it easy or clear someone was in there already or what kind of care the previous person had about the possibility of it having nylon gears... however someone felt like painting it orange.

The only other comment is my timing mark is exactly off by 10 degrees. It hasn't shifted in the time I discovered it and made a new mark.. I verified this with a piston stop, so I don't know if its possible the previous owner did change the timing set and installed the harmonic balancer incorrectly.

 

it's been worked on, you can see the lock washers on the pan and timing cover bolts. I'd be shocked if the original timing sprockets were still in there.

 

Forget it all. Your driving habits are perfect for what you have. Start changing things on an old motor and you'll wind up having to change more things which means $$. By the time you buy timing gears, cam, gaskets, etc. and add it up--divide that cost by the 150 miles per year you drive it-see what each mile will cost you vs. what you have now.

 

Thanks for good pictures.
Good move doing research first.
Swapping camshafts these days can go sour unless you get rollers

 

might want to put that bolt back in where the power steering pump bracket attaches?

 

Engine not torquey going up steep hills? What gears are you running? Might be running fine. But a heavy high geared truck with a smog engine wouldn’t feel like a monster going up a steep hill.
I’m also in the group saying you should just do the timing chain now. Not to mention the older I get the less I worry about a lumpy idle and think more towards reliability.
A lumpy idle cam, designed for higher compression ratio engines might make that truck even more sluggish going up steep hills.

 

Do I see both blue and orange paint?

 

I didn't take that out but yep I'll put a bolt in there!

 

Thanks! I have whatever stock gears are in it... the 350 motor with th350 trans. The rear end could be one of these three for the C-10 but not sure which: 3.07:1, 3.73:1 and 4.11:1

 

Oh ok, so they didn't come with lock washers by default but someone installed some? I wouldn't be super surprised if the previous owner(s) took care of replacing the nylon gear but I don't know how to tell for sure.

At this point will I gain much fixing it if I have 8 to 10 deg slack in the chain?

 

I already bought a Cloyes double chain timing set, fel pro timing cover gasket, oil pan gasket, harmonic balancer, ARP balancer bolt, and woodruff key and it ran me $171.73 with tax and shipping from RockAuto. I don't know if I can return it now.. everything arrived except the timing chain set and the woodruff key which might arrive by 1/4/24. I wonder if I can return and bitch at them it took a long time to get this stuff and "had to have someone else do the job"....

 

Didn't you say on your other thread that you didn't have full throttle travel? That could be your power limiting factor.....