360 engine vibration at ~3000rpm

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scott mattingly

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Guys(Sorry for the long post, but this is a 3-year story),
Have read content of various posts about internally and externally balanced crankshafts, etc.. but still have a question about my engine vibration & Noises. Situation:
-Bought a 74 duster a few years ago in pretty rough shape..for a fair price.(Bad vibration at 3000-3300rpm, slipping 727 transmission, but "rebuilt" 360 engine, solid body/great interior, 8-3/4 rear, 4-wheel discs; Fr&Rr sway bars, frame connectors, Hotchkiss rear leafs, ). Knew I had some work to do, but the "bones" were good....
-During trans rebuild found: broken 1 bolt btwn flex plate to torque converter, 1 broken flex plate bolt at crank, bad torque converter, and various internal damage to trans.
-After trans rebuild w new correct flex plate, new correct hole-shot torque converter, and all bolts....Vibration was still present ~3000-3300 but MUCH, MUCH reduced.(more like a bad exhaust vibration but still of a concern.)
-Factory style harmonic balancer is in-place and appears to be O.K.(Have not replaced it yet.)
-Since purchased, the engine has pulled strong (mild cam, long headers, edelbrock intake, 680cfm AFT carb..) but always had a loud tick(or low knock) under acceleration that many pals have diagnosed as a header leak, engine ping, etc... but was never loud enough to be thought of as bad rod/main bearing, etc..(Also never found any metallic "shiny bits" in oil.)
-TROUBLESHOOTING THIS SUMMER:
a) have slowed timing till engine barely idles smooth and mixed about 15% race gas into tank to eliminate possibility of detonation "pinging". AND: Noise still persists under acceleration but not when cruising down road at 45-50 on a flat stretch.
b) Gone through header/exhaust seals & everything is tight w no leaks
c) have gone through the rocker arms and replaced several to minimize any "clicking" as an aid to help identify the louder "knocking" sound. AND: engine is quieter but knock still persists.
d) installed fresh 20W-50W oil(have been using 10-40W syn. w Zinc add.) oil along with Lucas Oil Conditioner, AND: noise persisted w no changes.
OVERALL....Engine starts and runs good and can be revved in neutral to 2500-3000 rpm with no vibration or "knocking". I have not driven it "hard" and rarely go over 4000-4250rpm)
SO,..Am I kidding myself and simply have early signs/sounds of a failing rod/main bearing? Does the vibration at ~3000-3300 signify a crank imbalance or a bad harmonic balancer? Any other troubleshooting ideas before I start shopping for a crate engine?
THX-Scott
 
360s are externally balanced engines. To mate up your 360 to your 727, you either need a Summit Racing cut out solid flex plate for the 727 (not 904) to offset the crank external balance or you need the weighted torque converter to go behind 360s.

If you have a factory 4 eared flex plate then you need the weighted torque converter. If you have the Summit Racing cut out solid flex plate for the 727 then you need the neutral balance (no weights) torque converter to go with that.
 
Need some more info
What Harmonic balancer , the one with a cut out or the weight
What flex plate do you have , one with a weight or the one with the cut out
What about the torque converter , does it have a weight or two or nothing
Do you have poly engine or transmission mounts
What is your timing at initial and total, I know you said it is back but just covering ideas.
Was this engine previously balanced , any idea about the short block
Do you have pics of the parts that came out and then installed
I know there are several questions , just trying to narrow everything down.
 
I had the same issue with a 360. Turned out for me the motor was out of a four speed car and I didn't have the correct dowel pins in the block.
 
move the crank front and back see how wore the thrust bearing is. That is probably your knock due to a balance problem. The converter under pressure will move the crank. I already had the welds on the balance slugs on the back of the crank hit the block. You admitted driving this car like this for miles . I would say the thrust bearing is waisted. Move the crank see how far it goes front to back.
 
All good suggestions. I would add to make sure you don't have solid mounts (and the existing mounts are in good shape) and that there is nothing hitting the body, such as exhaust.
 
Guys, Al good feedback and ideas. Here are some answers:
1) Harmonic balancer looks just like pictures of the factory installed type. Has an offset weight.
2) Flex plate is one with a bite taken out of it (B&M #10236)
3) Torque Converter is neutral balance (B&M #10515) w 2400 rpm stall.
4) Driveshaft is an oversize steel unit by "Republic Diesel" in Louisville. I removed it & took to them after I purchased the car. They checked balance and confirmed proper length.
5) Motor mounts look like standard factory style and rubber looks O.K.
6) I have no details about the short block, pistons, etc...
7) Will continue to check for any contact points around exhaust/headers as they are pretty close in a few places(especially on drivers side.)
THX-Scott

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how are your driveshaft and ujoints ?
 
You said that there's no vibration in park, or neutral. That says the vibration is in the driveline. Drive the car, and pay attention to how the vibration feels. Then rotate it 180 degrees, and drive it again. Did the vibration change? Doesn't matter if it's better or worse. If there's any change, it's the driveshaft. If no changes, it's in the pinion angle, rear, etc.
 
furyus2 said:
You said that there's no vibration in park, or neutral. That says the vibration is in the driveline.

Not necessarily. You can get a vibration when the drivetrain is under load, which you don't have in neutral. The torque of the engine when in gear and under load transfers that torque to the whole drivetrain. Anything on the drivetrain that is close to the body or frame can move close enough to hit during acceleration (or deceleration).
Click to expand...
 
Maybe I assumed too much, but I would think that the op checked for anything hitting on anything.
 
Scott , have you taken the belt off and tried it? do that and try again if not. What kind of fan is on the engine.
 
Guys, All good suggestions. There is another piece of background I have that leads me to think checking the rear driveshaft angle is a good idea. That is:
--Since I bought the car, it had a sporadic "clunk" sound in the rear when going over a sharp bump (like railroad tracks). I crawled all under the car, tightened everything I could and replaced the rear leaf spring shackle bolts just to make sure everything was proper size and snug. But,.. the "clunk" was still there..once in a while..
---This Spring I was having a lower ball joint installed at a friend's shop and I asked him to look over the rear end while the car was on the lift. He found that the U-bolts on both sides of the rear end were not "very" tight.(though I thought I had checked them previously..?) He put an impact wrench on all of them and Lo & behold, the "clunk" was gone. Also, the car simply felt "tighter" when driving down curvy roads.
So,....it would make some sense that if the first set of torque converter/flex plates were incorrect and caused excessive vibes in the driveline, and the rear end U-bolts were a little loose, then...the driveshaft to rear differential angle could have moved. I am not sure how to verify this at home(is there a simple check/measurement to do?), OR maybe I'll take it to one of the local shops I trust. THX again, -Scott
 
before you break out that impact wrench know where you can get some u bolts
they strip or break, strip you can double nut
 
Wyrmrider,
Understood but there U-bolts have already been tightened and fixed the problem.(Double nutting them is a good idea.)
Jay27,
Have not tried to simply remove the alternator/fan belt. (car has manual steering, so I only have a single belt.) Car has a factory style clutch fan that work very well/smooth (had it checked out just after buying the car). Engine runs cool year round with this fan using a stock radiator and an external trans cooler.
THX-Scott
 
Gents,
I feel bad about not closing this thread out earlier, but here it is ..finally. The noise was from a BAD internal bearing of some type. I (& my local gear-head friends)expect a lower crank bearing due to nature and the sound as it became worse(2nd guess is a cam bearing).
During the last few times I drove the car in Oct and early November, the "knocking" noise became more pronounced and started at lower RPMs even when the motor was not under a load (like accelerating or pulling up a hill, etc..). Took it by a reputable/trusted engine shop and it was also their opinion that had it was an "internal" bearing failure. So,...
My pals and I pulled the engine a few weeks ago and delivered to a machine ship in Louisville Ky (Auburndale auto parts & machine shop) the week prior to T-giving. Plan is to: a) open up engine and determine cause of knock, b) if block(date stamped to be a 1970 block) is "good", rebuild as a 408 stroker engine and use the existing heads if they "check out"(may shift to alum. heads if mine are "not good"), c) deliver engine to Dale Meers engine shop in Buffalo Ky (about 20 miles fm my home) to break in Cam and "tune engine, d) put everything back together including TTI shorty headers I ordered ~2 weeks ago,..etc..etc...(Hope to be road-testing sometime in early 2021).
more to follow...-Scott
 
Good luck that car should be loads of fun to drive with the 408 the way you have it set up
 
Gents,
Though I have not yet re-installed my new engine (Covid concerns mainly), I did want to provide some feedback on this thread.
-I had my completed stroker(414 cu-in) engine broken-in & dyno tested at Dale Meers shop in mid-jan and the resulted are included in the pics below. Results were 490-ft-lbs at 3200 rpm & 419 HP at 5200 rpm with a 680cfm vac-adv. ATM carb.(which i am happy with) ..As per Dale, we could've achieved some bigger numbers with a slightly larger, mechanical adv. carb., but..(see below)
-MAJOR PARTS: Crank is part of an Eagle stroker kit with icon flat top pistons; Compression ratio is expected to be ~10.6; cam is flat-tappet Comp cams CRS XE274H-10 (.488 lift intake,491 lift ext.; duration @.050 = 230 intake, 236 ext.; lobe sep.=110 deg.); intake is an edelbrock air-gap 7576 intake; Heads are edelbrock 60179; roller rocker arms are Comp 1622,...& a few other goodies, like oil pan baffle plate, etc..))
-As you can see from the graph, the torque plot looks is on the downward slope at the far left. Since I have a vac. adv. carb., & their dyno uses a water-based torque converter as a load, it was not possible to get the secondaries fully open at lower RPMs. (Dale guesses it could produce just above 500-ft-lbs, with the existing carb. when loaded by pulling a car.)
-We did have some plans to try a larger carb, different Vac. adv. springs, etc.., but my original oil pan developed a couple of pin-hole leaks on its side where surface rust was present. It wasn't leaking badly, but it did need to be corrected, so... Dale's dyno guy (Nick) helped me replace the oil pan with a used Moroso pan they sold to me from their parts bin in the afternoon before I left their shop.
-Other interesting tidbits:
a) My engine is a 1970 block (see pic)which is apparently somewhat rare.
b) My old heads are nothing fancy (360 casting see# 4027596) and the engine builder (Gene at Auburndale in Louisville) convinced me to shift to edelbrock alum. heads as opposed to trying to work mine. (NOTE: I have these heads CHEAP for anyone that is interested; they were performing fine when pulled from the engine, had good compression, etc..)
c) I also have my original cam (see pics). I tried to cross the numbers stamped on the eng to a specific Comp cam model/grind, but could not find a cross ref.? (NOTE: I also have this cam available for anyone interested CHEAP. It was also performing fine when pulled and sounded pretty good with a noticeable lope at idle.)
d) THE LAST PHOTO is the reason my main bearings started to make noise which caused me to pull the engine. On 2 of the crank bearings, the previous IDIOT who "rebuilt" the engine, decided to put small pieces of brass shim stock btwn the bearing backs and the block (to try and fix a clearance issue I guess?). as you can see, it caused both of these bearings to wear excessively/fail exactly where these shims had been placed.
-----Any questions, OR for any interest in my "extra parts. just drop me a line..
-Scott

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If that is a Performer RPM intake, then the standard Performer would probably give better tq at lower rpms-with no loss at the top end. RPM is designed for 1500-6500 rpm range. Your engine is peaking at 5200. Perf rpm range is idle to 5500. With your greater cubes, that upper limit will be slightly lower than 5500 & should be close to ideal with your 5200 hp peak.
 
This does not affect your vibration, but in one post you said someone hit the U bolts with an impact. you guys REALLY need to buy and READ your factory service manuals. The leaf spring U bolt torque is low. It's only 45 LB FT. The reason is so the springs can actually "work" when the suspension jounces and rebounds. Over tightening those U bolts will result in the suspension binding and riding rough. You need to re-torque those to the proper spec.
 
Is that the air cleaner you plan on running? I would get a dropped base 14” in diameter housing with about a 2 1/2” element. Should clear the hood with the air gap. Also the throttle cable and kick down will need to be adjusted because the air gap is taller. That air cleaner will kill you.
 
Looks like there is a carb spacer also. Definitely check hood clearance.
 
scott mattingly said:
Gents,
Though I have not yet re-installed my new engine (Covid concerns mainly), I did want to provide some feedback on this thread.
-I had my completed stroker(414 cu-in) engine broken-in & dyno tested at Dale Meers shop in mid-jan and the resulted are included in the pics below. Results were 490-ft-lbs at 3200 rpm & 419 HP at 5200 rpm with a 680cfm vac-adv. ATM carb.(which i am happy with) ..As per Dale, we could've achieved some bigger numbers with a slightly larger, mechanical adv. carb., but..(see below)
-MAJOR PARTS: Crank is part of an Eagle stroker kit with icon flat top pistons; Compression ratio is expected to be ~10.6; cam is flat-tappet Comp cams CRS XE274H-10 (.488 lift intake,491 lift ext.; duration @.050 = 230 intake, 236 ext.; lobe sep.=110 deg.); intake is an edelbrock air-gap 7576 intake; Heads are edelbrock 60179; roller rocker arms are Comp 1622,...& a few other goodies, like oil pan baffle plate, etc..))
-As you can see from the graph, the torque plot looks is on the downward slope at the far left. Since I have a vac. adv. carb., & their dyno uses a water-based torque converter as a load, it was not possible to get the secondaries fully open at lower RPMs. (Dale guesses it could produce just above 500-ft-lbs, with the existing carb. when loaded by pulling a car.)
-We did have some plans to try a larger carb, different Vac. adv. springs, etc.., but my original oil pan developed a couple of pin-hole leaks on its side where surface rust was present. It wasn't leaking badly, but it did need to be corrected, so... Dale's dyno guy (Nick) helped me replace the oil pan with a used Moroso pan they sold to me from their parts bin in the afternoon before I left their shop.
-Other interesting tidbits:
a) My engine is a 1970 block (see pic)which is apparently somewhat rare.
b) My old heads are nothing fancy (360 casting see# 4027596) and the engine builder (Gene at Auburndale in Louisville) convinced me to shift to edelbrock alum. heads as opposed to trying to work mine. (NOTE: I have these heads CHEAP for anyone that is interested; they were performing fine when pulled from the engine, had good compression, etc..)
c) I also have my original cam (see pics). I tried to cross the numbers stamped on the eng to a specific Comp cam model/grind, but could not find a cross ref.? (NOTE: I also have this cam available for anyone interested CHEAP. It was also performing fine when pulled and sounded pretty good with a noticeable lope at idle.)
d) THE LAST PHOTO is the reason my main bearings started to make noise which caused me to pull the engine. On 2 of the crank bearings, the previous IDIOT who "rebuilt" the engine, decided to put small pieces of brass shim stock btwn the bearing backs and the block (to try and fix a clearance issue I guess?). as you can see, it caused both of these bearings to wear excessively/fail exactly where these shims had been placed.
-----Any questions, OR for any interest in my "extra parts. just drop me a line..
-Scott

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Click to expand...
Over the last 4 decades I have seen some shoty engine builders handy work but putting shims under a main bearing, that's a new one.
Chalk one up for Hall of Shame.
 
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