72 455 popping at carb and clunk

Hello everyone ive experienced my car backfiring through the carb along with an intermitent clunk from what sounds to be in the lower part of the engine. I was thinking crank or possibly the timing gears as im not sure if the 72,had the plastic teeth aswell on the gears. Ive been experience consistant overheating issues of which prompted me to looking into doing a rebuild anyways. I purchased the how to build performance buicks book, but is it realistic for me to assumr to do this job myself. Ive contacted several knowledgeable builder but i simply can afford them at this point, and figure i could save a ton of the money if there was little to no labor charge. Please lmk what you guys think and feel free to tag me in any posts of anyone that has attempted this before.

 

I cant comment on what to do with your current motor. I can comment that I built my own Performance 462. So far so good. I took my time and listened and read a lot of build threads on here. I got lucky and found other peoples dreams. I bought a fully built Shortblock, forged pistons, sportsman rods, girdled, dual grooved cam bearings, BHJ Balancer, JW FlexPlate, machined crank, and all bearings for 2500 bucks. If you look into what it costs to do what I just listed it costs a lot to have it done. Girdle work is over 1,000 by what I understand on its own. I then Bought Stage 1 Aluminum Heads, got entry level port and polish from JW at Trishield Performance, got him to also work over my timing cover and oil pump. The cost around 3,300. If you read up on where you put your money its n the heads. I scored a deal on used TA roller rockers for 250, got long tube hooker headers for 300 brand new, another good deal. I got a Edelbrock Aluminum Intake for 270 with shipping, a redone 800 cfm qjet for 175 from Ken at everyday performance. he had a customer that backed out on a deal, I got lucky and was first in line. New distributor, valve covers, air cleaner, camshaft and I am sure there is more but that is the most of it. that rounds up to 7200 roughly for a built Big Block Buick. You could do a little better if someone sells there aluminum heads on here for a deal. That is the only part I could not find for less than retail on this site. that is if you want 500+ HP that is streetable. It wasn't easy by any means. If I did it all again I would just buy a whole turn key car. This car ended up being my education tool though that would give the confidence to buy a turn key car that I could now work on all by myself. Back in 2012 when I started this adventure, I was reluctant to buy a nice car and then have the possibility of things breaking and me not knowing what I was doing to fix it.

If you just went with what you have, reworked the Iron heads, if the stock rods and pistons are good recondition and reuse them, Do a general rebuild you could get it done for a lot less. Just may need a good machinist. Just depends on your goals and what you want/plan to achieve. If you rebuild it stockish you'll be fine, if you let it snowball out of control like I did you see what that did. You also have to keep in mind, I had to get a beefier transmission, better driveshaft, rear end, driveshaft safety loop, better radiator and I'm sure some other things to support the power the built 462 will make. If you stay stockish your stock driveline will be fine. If you build the snot out of it, and do not upgrade what's behind it, it will eventually show you where the weak links are. So take it slow, think out what you really want to do and how much your willing to really spend in the long run. There is tons of knowledge on this forum on what to do and what not to do when rebuilding the 455. Study and learn as much as you can. Good luck either way.

 

I didn't say it but the heads were 2900 all on there own before 100 bucks for shipping.

 

Running hot and popping back out the crab all of a sudden go hand & hand to me with a shot timing chain and gears and is super easy to check!

 

Overheating problems need to be addressed before a rebuild, especially if compression is increased on the new build because the new engine will make more heat with more compression. Even with the same compression the new rebuild will more than likely still make more heat than the old one because of better ring seal with the new engine creating more heat than a worn out engine.

Put a timing light on it to see if the timing is off from a possible worn out timing gear, that could be the root of all of your problems right there that you need to replace the timing set? This is the first thing to check.

To check to see if the stock nylon coated cam gear is still in your engine(yes they still used those crappy nylon gears into the 80s IIRC) remove distributor and look in the distributor hole to see if you can see the cam gear, if not the distributor needs to come out to remove the timing cover anyway because that is the only other way to do a visual inspection.

If everything else is good, do a compression test to make sure all cylinders are close to the same. I suspect that you may have a wiped out cam lobe if the timing is good and that may be why its back firing through the carb? Or a crossed wire could be the culprit? So double check to rule out a crossed wire. Or could be the carb? The compression test should be done first though to rule out a wiped out cam lobe.

As far as the "clunk" that could be the thrust bearing allowing to much fore and aft movement or detonation from the timing being off? But seeing how it is running hot, that would indicate that the timing is retarded which wouldn't cause detonation. With a bad timing gear though your timing could be jumping back and forth as well causing the "clunk" and the overheating?

Well this should give you a few areas to check before you plan on a total rebuild. GL

 

Man guys thanks so much for the insight, imma start here, and definately keep you guys posted with updates, questions and progress. I had planned for plenty upgrades but no need of it looking good and running like crap. Thanks again at least i have a base to step off from now.

 

As far as your clunking goes, you said its intermittent, which would tell me its NOT bearing related, bearing issues are usually rhythmic, knock,knock,knock.

 

Hey mark im sorry it is more in a rhythm, i can usually time when the clunk is going to happen, since it started this ive limited running times as im unsure of the magnitude of the damn till i have time to start to tear it appart to start searching. I have a video but cant get it to load here where you can faintly hear the clunk, its hard to hear as there is a exhaust leak that makes it run loud, do to a poor job from the muffler shop.

 

If the knock does not get more prounced with applying the gas then it's not piston slap / wrist pin or bad rod bearing Related atleast!

 

So guys I finally had a chance to start the tear down of my engine. Got the cover pulled and found he original nylon gears and slack in the chain (lmk if what you guys think), and the hold down for the distributor was loose, but I'm gonna see about continuing my rebuild. Timing was probally way off from these two things alone! Once i pull the engine what is the first step I should be doing as far as the machine shop I'm looking for 500hp + . Thanks guys

 

There is a sticky in the street strip section about the oil mods needed. Along with advice on how to build a 500 HP BBB. 230ish duration cam, it doesnt have to be a huge cam to make that power and high lift cams are dogs on the street unless you run a huge stall or drive it like you stole it all the time, so I would not go that route for a street car, 525 to 550 lift with 230 ish duration with roller rockers will easily get you there if your heads flow enough air, tot hat note, Good flowing aluminum heads is the easiest way to get there. Generally the money you sink into Iron heads will get you to out of the box aluminum heads. there are several ways to go for piston rod combo to support 500 HP. YOu can recondition stock rods with TRW or SRP pistons but a lot of block decking must be done. Or there are Piston and rod combos from Jim Weise at trishield that get you more cubes and less block decking. That is just a general overview. Study up on this forum on other peoples builds. Mistakes and things they did that will help you along the way. I'm sure others have more knowledge than I do. Obviously new timing chain and gears. Good Luck.

 

Any chance you feel like putting a new chain and gear on then getting it timed up right and do a full
test on the current possibly good running engine? Pretty cheap and would use parts that are
useable on the rebuilt version if you head that way.

 

Yep 67skylark27 , im definately going to do the timing set, but since I'm going into it anyways I figure I may as well do the oil mods cause it will need them anyways. I was thinking of switching to HEI and doing the mild mutha thumper cam also. My question is does anyone know if that cam can be used with keeping my stock pistons, lifter and rockers. My plan is to change, the timing set, add HEI, Edelbrock b4b intake and edelbrock aluminum heads. Will this combo work well together along with giving me a little more than a stock motor?

 

New cam=New lifters!

 

Yep I meant stock, rockers, and push rods, but if I remember right I may need long push rods to accommodate the new heads.

 

Well I found the source of the clunk..... looks like two of the retainers for the rockers have broken, one of which was allowing the rocker to slide back and forth on the shaft causing the clunk. That same rocker has a bent pushy or also. Not sure what kind of damage is further down ill possibly find that out tomorrow

 

If you look closely at the rocker that's kadywompas, it looks like it cracked.
HOPEFULLY that's your only issue
The exhaust valve not opening was the source of your popping/backfiring thru the carb.
The burnt air/fuel couldn't get out thru the exhaust valve because of the broken rocker, so it tried getting out the intake valve when the intake valve opened

 

Well I see I'll have to replace all gaskets this thing was leaking from everywhere. I'm also doing the bare minimum oiling mods, can someone tell me what cause this scoring on the pistons a valves and what's the reecommended way to clean them without harming the pistons.

 

Don't see any pics. of the pistons