Technical Changing Cam on a stock SBC 350

I remember reading that too. The smaller lighter chain probably used slightly less power, as well.

But he didn't use plastic covered aluminum sprockets that had 60k miles on them. He got new ones.

 

Apologies for any offense.
Have read most (skimming now ) but here is where I'm at.
Forget all of us, but before you get all into it,,,
Find yourself an old time mechanic. Approach him with a dozen donuts and a twenty dollar bill.
Ask him to drive you up the steepest hill he knows, and tell you what he thinks.
That decade had the engineers running every which way.
Hoping to give us an economical, and inexpensive power source.
You'll owe him nothing, just listen to his experience

 

Naturally, and I don't recall how often they were changed out. .720 rollers had to be brutal...

 

IF you're willing to do the job of replacing the cam and timing chain, it sounds like you're willing to put some work into the truck. I would just run it as is and just maintain whats on there until it goes out, then put work into it. Even IF there would be catastrophic failure (I've change quite a few sheared nylon gears without internal issues, just cleaning the pan out), the worst issue is getting it towed back home. You don't need to rebuild the engine if you don't want to, just find another used engine (350s are EVERYWHERE), toss on your new parts and that will outlast the body.



BTW, it's super rare to see an intact nylon gear set up in 2023/24. Almost all of them have been changed or even rebuild by now. I happen to have one in great shape as it was in my '41 Ford pu (1978 target 350 from a dealer), had very low miles and sat for 35+ years.

 

There it is. Thank You

 

Thanks, makes sense... unfortunately I jumped the gun late December and bought all the cloyes double roller timing set and gaskets and it came out to $171 from rockauto.. it would cost me $50 or so to send it back since shipping wouldn't be refunded... that being said my thought is if I have the parts i may as well change out the timing set knowing there is some slack. It wouldn't make sense to just sit on the parts until the failure happened ? (which may never happen in my lifetime at 150 miles per year) That would be the last project on my list for this truck... already rebuilt the rochester 2G carb and it felt fine around the neighborhood.

 

@squirrel I may have asked the question incorrectly. Do you think I should advance the timing given the crank sprockets for the cloyes double roller set have three keyways for timing adjustment--4 degrees retarded, 4 degrees advanced, and normal. I understand by default it will advance some given I currently have 8 degrees slack.

I read some people want more low end rpm torque so they use the 4 degrees advanced. Will that open up any can of worms with a stock engine with the low-ish compression numbers I shared before? I tend to drive non-freeway most of the time (90 to 95%) and do climb a moderately steep hill to get back home every time.

 

What I meant by "set it to Zero", is to use the timing chain setting that neither advances, nor retards, the cam timing. Leave it stock. I think that's the O (circle) timing marks on a timing set like that, but read the instructions to be sure.

If you are running a big cam, then advancing it a little might be a good idea. But with an unkown but probably stock cam, you're only going to get low end torque anyways.

 

Got it! Makes sense and thanks so much! I’ll update when I’ve got the timing cover off I’m super curious to see what’s there!

 

I wonder how a chain wears. Let's assume it's equally. Your 8 degrees of slop would thus result in +4 to -4 degrees. Given an amount of slop in the chain I suspect the cam must be dragged around by the chain (any pushing being lost in the slop). Thus, as you are, I'd guess that you're 4 degrees retarded, and possibly as much as 8, and not advanced at all. Crazy theory huh?

Chris

 

Yea, what I think would happen is with the new timing set it would advance at least 4 degrees (from where I'm at now) even setting the crank sprocket at zero setting.

 

The new timing chain will correct the 4 degrees that it retarded from wear.

On a stock wheezing GM cam you wouldn't even notice this [because they are short duration anyway]
And you correct any ignition timing with a timing light.

 

You do realize that timing cover is not going to go back on with out some mods if your trying to use the factory rubber oil ban gasket and there is a high chance its going to leak when done .

You will need to trim the ears on the rail on the back of the timing cover and then some how get it back in and sealed with some silicone gasket sealer. Its a PITA if you have never done one . the engine was desged to put the timing cover on first then the oil pan over it.

permitex right stuff is the best bet IMO for this and not the fast dry stuff your going to want time to work

 

Well, for the few times I’ve done this with the engine in place in the vehicle, I drop the oil pan down, put the timing chain cover in, then snug the oil pan back in place.
More work and a PIA, but only thing that worked for me.

 

Thanks, won't I be fine if I'm planning to drop the oil pan? That was my intention. I'm also hoping there is enough room for me to snake the pan out entirely (without raising the engine) so I can see whats at the bottom of it and clean it. At a minimum I'll drop it and clean off the old gasket carefully and put the new one on.

I ended up getting this gasket for the oil pan:
https://www.summitracing.com/parts/fel-os34510t

also this gasket for the timing cover:
https://www.summitracing.com/parts/fel-tcs45121

 

If you wanna add some flash along cutting a little time and replace the front seal in the process I actually used a chrome timing cover from AutoZone. Used the supplied gasket and bolts too. Hasn't leaked a drop. Plus was a lot less cleanup. And like $20

 

Cheap chrome and salt air don't mix. Even with constant cleaning it still rusts here.

Another thing I would look at while you're at it is all the core plugs (freeze plugs), make sure they're not crusty.

 

yeah I’m not far from the coast and I left this truck outside the first year I bought this house and saw some of my chrome parts not liking it at all (air cleaner in particular) I replaced them and now it lives in my garage now.

 

@squirrel The more I go through this I'm realizing someone put this engine together and molested it and who knows what other car it was in before it made it into this truck. The Rochester 2G carb is from a 1969 year vehicle. I found a stamp code on the block a little near the waterpump on the passenger size that says V0916TXA and I read the TXA suffic is a 1975 chevy 4 bbl with 165 hp rating. I guess someone decided to change from 4bbl to 2 bbl. ... seems the opposite direction to head! The 1975 350 motor with 2bbl is rated at 145 hp. Maybe that person wanted the 4 barrel for something else and snagged the carb/intake off the motor?

Do you think I'm actually losing 20 hp staying with the Rochester 2G given maybe the cam/heads would be set up from factory for a 4 bbl? When I had the valve covers off when doing seals I took a photo and found the heads have number 462624 and read those are 76 cc smog heads and not that good at all.

At the same time this engine is filthy on the outside... if this truck did'nt have so much rust I would be willing to put money into it and put a crate motor into it and call it good... but I don't want to put much money into it. I rebuilt the Rochester 2G and I'm sure it will perform better than it did before... just wondering still if hunting a 4bbl intake and quadrajet would have been worth it given I am already running with low Hp and every bit could help... although the lower compression ~120 psi on average for the cylinders sort of gives a clue maybe this motor isn't worth the time/money for converting back to 4bbl. Even though the 4 bbl to 2 bbl likely dropped this engine down 20 hp, it has dual glasspack exhaust, the smog parts removed, ram horn exhaust manifolds (supposed to flow better than the crappy smog era manifolds), and I installed an HEI distributor so maybe I'm back to the 165 hp.

I read the smog motors came with restrictive exhaust manifold, single exhaust, and points distributor, smog pump/canister.

 

Restrictive exhaust manifold ? Yea , over 5000 rpm ! Points distributor didn't " loose" horsepower . smog pump & canister " maybe" cost a HP or two . If the truck is a rust bucket , anything more than getting it running is an exercise in futility .

 

The 350 engines in the 70s were available with 2bbl carbs in some cars, and in some trucks. These had heads with smaller valves (same large chambers though).

Points were last used in 1974, they went to the HEI in 1975 on all of them.

This is the torque and power ratings for the 1975 full size Chevy cars. The ratings are "NET", which means they compare with ratings back to 1972, but before that the ratings had been "GROSS", which was about 30% higher. So don't compare these numbers to 60s engine HP ratings without taking that into account



The thing you might want to look at when you're deciding 2 or 4bbl is the torque rating of the engines. Turns out the torque rating is the same for the 2 and 4bbl version of the 1975 350 engine. But the HP is higher, but just a little, and both at the same RPM. It could be that this was limited on the 4bbl engine by the very restrictive early catalytic converter single exhaust. Even so, most of your driving is at lower RPM, and the 2bbl is making just as much torque as the 4bbl at these engine speeds, so you're not really likely to gain anything until you hold the pedal down, enough to get the engine well over 3000 rpm. How often do you do that? (yeah, that's where the action is, so I can sure understand the desire to improve it)

If you're using the truck for transportation, then building up another engine to replace this might be a wise way to go, instead of trying to slowly increase performance of this one. Or not...depends on a lot of things that I don't know.

I do know that my 62 Vette with the low performance 327 could sure use a bigger carb, intake, valves/ports, and exhaust to "wake it up" over 4000 RPM. But it turns out I'm pretty happy with how it runs and drives with the restrictive top end. It has just as much torque at the engine speeds I use 99.9% of the time while driving, as it would if I hopped it up.

Tough call, but it's good to have realistic expectations about what you might gain with modifications.

 

Just to confuse you more, here's the same chart for 1971, with the gross and net ratings. The engines were pretty similar from 71 to 75, there were minor internal changes, but the biggest change was the addition of catalytic converters in 75.



Keep in mind that it was really easy to wake up any of these engines by adding headers and a bigger cam. Swapping intakes and carbs usually didn't gain very much unless it started as a 2bbl engine, then the higher RPM power would increase noticeably. But if it started with a 4bbl, the improvement was not much different than running the original intake and Quadrajet carb.

 

yeah makes sense I just happened to read an article on a nova with a smog 350 where they made a few small similar changes and quoted it having increased performance /hp without anything else major…. I agree I’ll finish the timing set today or tomorrow and close this thread out

 

Thanks although I understand I’m overthinking I’m definitely enjoying the learning part of this more so hearing other perspectives and not just reading purely from articles or older threads… however I’m planning to finish the timing set today or tomorrow and will stop at that!

 

Be sure to get a picture of the old timing chain, right after you remove the timing cover.

 

For me this will be a moment of truth given all the convo.. the first thing I'm doing when that cover comes off is taking a photo and posting on here. I'm predicting the original nylon timing set was changed out.

 

You were right the cover had been off and I didn’t need to worry about the nylon gears! @The Chevy Pope check this..

I noted a 10 degree offset at the harmonic balancer with the timing mark indicator on the timing cover when I found TDC using a piston stop. I compared the new harmonic balancer to the one I pulled off and bingo.. the new one looks where I expect zero to be.

I set it at TDC #1 on compression stroke before taking off the timing cover….

When I look at the new cloyes timing set parts the crank zero would be at 12 o’clock and the cam zero would be at 12 o’clock too. I think that’s correct at tdc #1 compression?

there was a lot of slack in this chain though!!

the bigger pain right now seems the oil pan… I’m going to have to take the starter out and see if I can drop the pan enough to work the one piece gasket in or even pull the pan all the way off if possible.

 

That all looks normal to me....the sludge indicates the engine didn't get oil changes as often as it should have.

When setting the cam timing on a SBC, it's normal to put the cam dot at 6:00, and the crank dot at 12:00, and totally ignore where the pistons are.

But you have to get the engine back to TDC #1 firing position to get the distributor back in!

 

probably! I change the oil once a year even though I drive it just 150 miles per year. I changed the oil last July but I’m about to drain it all to get the pan down.

I see. Since I happened to put it at tdc #1 compression and the distributor is already in I would use 12 o’clock for the cam?

 

Note two washer head bolts and one regular bolt with lock washer on the cam gear.
No big deal but yeh, people been in there!