Light white smoke and backfire at high RPM or under load

[iflyfisher]

@squaredeal91, I never replaced a cam, but based on a bit of research, it doesn't look too bad, and looks like I can do it with the rest of the block still in the truck. I can also take care of the timing chain then.

I jumped onto Summit Racing to look for camshafts and over 600 results popped up for this 350! If I search for stock replacement, five cams are in stock. A Melling CCS-2 and several COMP Computer Controlled Cams. I looked through the service manual, and I couldn't find reference to stock Lift and Duration. How do I know which to buy? Maybe all five are considered mild and doesn't matter much. Dunno.

 

[squaredeal91]

I'm sure someone on here more knowledgeable can help with cam choice. I've changed lots of them but I'm not the numbers guy lol.

 

[iflyfisher]

May call the machinist next week. He is an engine builder and can likely give me a recommendation.

 

[RanchWelder]

Do not be afraid of the case hardened Melling Stock cams!

There's millions of them and they work.
If you try to out smart the General with aftermarket on a low dollar rebuild, you will lose...

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Send a reasonably good OEM cam to be re-ground to your machinist's recommended profile, or ask if they have one off the shelf to save you money. They probably do.

Fill out the form, send in a hardened OEM cam and build it right.
Melling is your friend. Using an OEM cam and regrinding is the new cool thing to do. Cuz it works and lasts!

The chain worrying you, is a good thing. It's your Dad's truck, rebuild it right.

Change the gears with Cloye's best. Make certain you get the correct set before you push the buy button.
Or buy OEM GM set. Either way, it's from the same supplier, just cost more.

If you start that engine with a history of bent or leaking valves, with the worn out chain; you will fail.
The suck will be brutal. The agony will hurt you as a person. Try not to fail.

The cam removal means new seals and hardware, if required.
There will be signs of cam bearing wear, when you machinist inspects your cam. If he see's excessive wear, your bottom end might be damaged too. So start with your cam!

I know you just bought heads, but if the cam shaft wear is excessive, you might be pulling the trigger too fast in the wrong direction.

There's a certain quality about your posts, that tells me you want this right, at a budget.

This is where everything counts. Good Luck!

 

[iflyfisher]

@Welder, you were up late or very early . Not necessarily trying to get the ol truck running on the cheap. This is simply my first rodeo. I've done a fair amount of wrenching on motorcyles, but never the big boys. I figured this non-emission and non-computer controlled truck had the perfect engine for me to learn on. I also want to keep the matching original engine in the truck, which is why I am focused on getting this engine running rather than rushing out to buy a rebuilt or crate engine. I am not so much budget conscious, but rather I am groping my way through getting this old engine running. I retired a few years ago, and I do have time, so this project is perfect. I was trying to avoid pulling the heads, but when nothing seemed to fix the poor compression in two cylinders, I had no choice. The heads are original, I am simply having them rebuilt. I can't do anything now until after the new year. But I will be talking to the machinist about the cam. The engine has 100K miles on it, and my Dad religiously changed the oil. So, I am hoping the bottom end is okay. Only one lifter had issues, and that appeared to be due to it not rotating. I don't know if cam slop would show up on some of the lifters. All the rest looked fine. If I need to pull the block and rebuild the bottom end, I will. But again, I'm hoping not to.

 

[RanchWelder]

Good News. It's tough to gauge what level of experience in these threads.
Recommending parts and service tips without burning somebody with a tight budget can easily happen.


You'll never have to guess about any engine you install ever again.


Merry Christmas!

 

[iflyfisher]

OMG @Welder, you just opened up the firehose! Thanks for taking all the time to jot this down and share the video links. I was 'hoping' not to crack open the bottom end other than to loosen the oil pan so I could take off the timing chain cover. I need to read through this a few times to understand all your recommendations. The engine is still in the truck, so I believe much of what you suggested would be done with me lying on my back.

I like the idea of at least checking the main thrust bearing. I think I am going to have to drain the oil anyway to loosen the oil pan to remove the timing cover, so I might as well take off the pan completely and check that main thrust bearing as you recommended. Regarding the pistons and rings, I checked compression on all the cylinders and the numbers were 143 to 150, except for 6 and 7. I have my Dad's old log books. I found an entry back in 1975, and the compression figures he measured back then were pretty much identical to the ones I measured 48 years and 80K miles later! Once I pulled the heads, I tested 6 and 7 for valve leaks as noted previously in my thread, and the valves did leak. So here I go hoping again...but given that, I hoped the pistons, rings, and cylinder walls were all okay. If I were to pull a piston, it would be cylinder 6 or 7 as I never had good compression numbers for those two. I have been hesitant to pull a piston as I thought I needed to hone the cylinder to remove the piston. Like pretty much most steps in this journey, I don't have that tool either.

My thinking has been to work from the top down with the engine still in the truck. If I got through the top end, and the engine still was not running right, I'd pull the engine and take it to a machinist to rebuild the bottom end, assuming the engine is worth rebuilding. If my machinist looks at the cam and says the bearings should be okay and I measure the crankshaft end play and find it within tolerance, I'm inclined to stop there given the good compression numbers I got prior to pulling the heads. If the compression on 6 and 7 doesn't come up after reassembly, I'll pull the engine and look into rebuilding the bottom end with a possible bore and piston/ring replacement. You had noted to replace the oil pump if I did the full meal deal with rings. Would you recommend replacing the pump if I don't dig deeper into the bottom end? I don't know if the pump can be replaced with all rods and bearings in place.

My Dad had a service manual for the 1973 vehicles that shared the 350. I downloaded the 1973 light truck manual from this site. It doesn't have as much on the engine as I was expecting. I'll also look into the snout socket tool you recommended. I've been doing a lot of plug pulling to turn the crank.

Merry Christmas to all well!

 

[squaredeal91]

I always add a high volume oil pump on all mine and check the rear most main bearing at the same time. I take it off, look at it change rear main seal and call it good. Pan should come off before timing cover and back on after timing cover. Pan should come off without picking up engine.

 

[RanchWelder]

Every engine rebuild should include a new highly polished oil pump, in my opinion.

 

[iflyfisher]

Thanks for all the input gents. This thread is a good reference for me and likely others going through a similar project. Appreciate you sharing your knowledge.

I talked to my machinist this morning and he recommended a cam. This afternoon, I ordered the cam and lifters (COMP cam kit), timing chain and gears, ARP head bolts, thread chaser, oil pump, water pump (figured why not), fresh v-belts, fresh radiator hoses, crank snout rotation adapter, assembly lube, break-in oil, and a variety of gaskets. I was going to get some LocTite sealant for the head bolts, but Summit wouldn't ship it my address.

My machinist agreed with checking the thrust bearing play and said he would be very surprised if the play was too much. I asked if he wanted to look at the existing cam once I pulled it to see if the cam bearings might be bad. He said given the mileage on the engine and all other lifters were fine, he didn't suspect any issue with cam bearings but told me to take it in when I pick up the heads. He also said if the cylinder walls look okay on the two lame cylinders to not even worry about pulling the pistons to inspect the rings. He is certain the low compression was due to the valves. Given how certain he was about this, I didn't pick up tools now to hone the cylinder and install the piston. If we are wrong, then I'll pull the engine later and do the bottom end.

Looks like 2024 will start with some wrenching!

 

[SquareRoot]

Roller cam and forget about it. The savings in using regular oil will eventually pay for the difference in cost. Flat tappet cams ought to be banned. Break in oil....lol

 

[iflyfisher]

Well…that doesn’t help much at this point.

 

[RanchWelder]

Honing is not generally done with the engine installed.

 

[iflyfisher]

Gents, I appreciate the concern about my old 350 being behind from a technology perspective. But, I'll probably only put a couple thousand miles a year on it once I get it restored. Perhaps if it were going to be my daily driver and see a lot of miles, I'd go with the roller cams. Others have also suggested to drop in an LS or at least switch to an HEI distributor. Frankly, I kind of want to get this truck running the way it was originally. I know it is old school. I'm not ignoring your suggestions. I just don't want to go there yet. Yeah, I'll be giving up performance, some fuel economy, and some longevity, but that's okay.

 

[squaredeal91]

I'm with ya there^^