Topic: weirdly loud noise from engine - youtube link posted

[Xander^]

would anyone happen to know what this sound is on my bike?
this was the first start up since the rebuild.

rundown:
-1977 cb750k
-top end engine rebuilt
-carbs cleaned and rejetted for airfilter and exhaust

not sure but only thing i can think of this noise is coming from the engine.. thought maybe the rocker arms hitting the cam cover?

it gets louder when i rev the throttle.


in the shorter vid attached, the sound seems to be a lot quieter but the idle was so low that the bike died out. im losing my mind.. will i have to open up the engine again?

[jakec]

It's hard to tell the if the tone is accurate, but the easiest thing to check would be the pipes, see if you're on all cylinders. Then if so check to see if the slides in the carbs are synced.  In either case the pistons will make a loud thump as they fight each other going around the crank.

Another thing that happened to me once with a CL175 was a loose spark plug, with every stroke of the piston it was getting smacked up and down like jackhammer. It wasn't this loud though.

Other than that I'm not sure. It sounds way too loud to be the valves. And it doesn't sound exactly like either of the things I described above. But it's hard to know from computer audio.

[Jerry Rxman Griffin aka MuthaF'er]

Can you "feel" it with your hand on the head or cases?

[Deltarider]

Hard to believe it runs on all four.

[Xander^]

Can you "feel" it with your hand on the head or cases?

Ill will try to see if I can when i start her up again. I took carbs off to get them rechecked, seems like now my new float on number 2 carb isnt doing its job, im getting a flooded bowl and its leaking out of the airbox.

[Xander^]

It's hard to tell the if the tone is accurate, but the easiest thing to check would be the pipes, see if you're on all cylinders. Then if so check to see if the slides in the carbs are synced.  In either case the pistons will make a loud thump as they fight each other going around the crank.

Another thing that happened to me once with a CL175 was a loose spark plug, with every stroke of the piston it was getting smacked up and down like jackhammer. It wasn't this loud though.

Other than that I'm not sure. It sounds way too loud to be the valves. And it doesn't sound exactly like either of the things I described above. But it's hard to know from computer audio.

Good idea on the spark, going to cross that off. Sorry this is my frist bike so im not sure how to see if im running on all 4 cylinders ..lol. You say this is easy?

[jakec]

It's easy to check. I'll let you figure out how just be careful

[Xander^]

It's easy to check. I'll let you figure out how just be careful

well if u meant just by taking a hand to the exhaust, that ive done, all 4 were hot to the touch and i guess that means its running all 4? unless there is another way or you meant something else?

[Jerry Rxman Griffin aka MuthaF'er]

Take your hand to the head, cylinders and rocker cover before they get very hot.

[Xander^]

here is the video on youtube, probably a lot easier for everyone to view.. can really hear the loud taping/clicking

[scottly]

Thanks for the youtube link; I couldn't view the other ones.
The noise sounds mechanical, but not like tappets? Do you have oil pressure? Did you fit an earlier clutch cover? It almost sounds like a very bad exhaust leak at times? You might try holding on end of a piece of tubing next to your ear, and probing around with the other end?

[Tracksnblades1]

Does it change when shifting in gear with clutch lever engaged?
Did your cam chain guide and tensioner give you any trouble going back together..?
You did get all em rod bolts torqued , didn't you...?

[754]

Check your valvecovers, see if the adjusters are tight..not saying it would make that sound.
 Did you by chance, change to an early head ? Or get an exchange head ?
 The head shoukd be marked with a number, top fin at the back in the middle.. on that year.

[Xander^]

Thanks for the youtube link; I couldn't view the other ones.
The noise sounds mechanical, but not like tappets? Do you have oil pressure? Did you fit an earlier clutch cover? It almost sounds like a very bad exhaust leak at times? You might try holding on end of a piece of tubing next to your ear, and probing around with the other end?

yeah i believe oil pressure is fine, i dont have a gauge on atm but i know im getting oil into the engine, i had a minor drip leak in the clutch side cover (bolts just needed tightening)..i didnt NOT put an earlier clutch cover... carbs are off and send to re-inspect with a friend so i can try that when i re-install them and start her up again.

[Xander^]

Does it change when shifting in gear with clutch lever engaged?
Did your cam chain guide and tensioner give you any trouble going back together..?
You did get all em rod bolts torqued , didn't you...?

YES it went into 1st gear without an issue and i took it up and down the driveway, but thats all because front brakes arent on yet and no seat lol.

i got a new cam chain guide installed. the gent that rebuilt my top end didnt have an issue with anything that i know of.

i actually installed the tensioner afterwards because i cleaned it up and painted it.. maybe i didnt adjust it properly?

[Xander^]

Check your valvecovers, see if the adjusters are tight..not saying it would make that sound.
 Did you by chance, change to an early head ? Or get an exchange head ?
 The head shoukd be marked with a number, top fin at the back in the middle.. on that year.

ok i will confirm the adjusters.

no i havent changed to an early head, unless it was changed before i bought the bike... but before tear down/disassembly it didnt sound like this... ill confirm tho

[754]

Just look at the number on back of the head.

[MCRider]

ugh wow that sounds terrible. I'm posting to get notified as you progress.

I just made a vid of my rebuild, a 900cc with all hi-perf parts, if you want to hear what one is supposed to sound like.

I did have my share of problems, but it sounds like a sewing machine now.   

[Xander^]

ugh wow that sounds terrible. I'm posting to get notified as you progress.

I just made a vid of my rebuild, a 900cc with all hi-perf parts, if you want to hear what one is supposed to sound like.

I did have my share of problems, but it sounds like a sewing machine now.   

yeah.. not really any good news yet. im going to try to uninstall and re-install the cam chain tensioner properly with the engine turned 15 degrees pasted dead top on number 1 cylinder.. apparently thats how you have to install it..

[MCRider]

ugh wow that sounds terrible. I'm posting to get notified as you progress.

I just made a vid of my rebuild, a 900cc with all hi-perf parts, if you want to hear what one is supposed to sound like.

I did have my share of problems, but it sounds like a sewing machine now.   

yeah.. not really any good news yet. im going to try to uninstall and re-install the cam chain tensioner properly with the engine turned 15 degrees pasted dead top on number 1 cylinder.. apparently thats how you have to install it..

Its not that its how you install it, but how it needs to be when you adjust it.

Take the CCA off the back of the engine, Loosen the lock bolt and depress the plunger into the spring as far as possible and lock it down. Then reinstall the CCA to the engine, Then set the engine position as per Hondaman and loosen the lock down bolt. You should hear an audible "snatch" as the plunger pushes into the internal adjuster parts right smartly. Then lock it down.

I don't think that's your sound tho. 

PS:

I thought HondaMan was in this thread?

To set the engine for CCA, remove the sparkplugs, to reduce presssure on the ignition drive bolt. Remove the number 4 intake tapet cover. Turn the engine forward using the 23mm nut on the ignition rive stud till the #4 int tappet goes down then back up. Now watch thru the ignition inspection hole for the 1-4 TF indicator. Turn past that till the left side of the spring post lines up with the mark on the crankcase. That's 15deg ATDC. Now loosen and retighten the CCA lock down bolt. And then the lock nut.

[754]

What I am possibly suspecting is..
 Earlier head, with late pistons, and pistons smacking the head..
 The noise seems constant..

[Xander^]

thanks Rider... im going to do this all tomorrow evening.. i have no other leads to what this sound could be.. im getting extremely worried. before the top end rebuild i had sent the engine for it didnt sound like that.. guy who did it said everything went back together the way it was supposed to and does know what the sound is


and ill also check the head numbers to get an idea of year... ill lose my mind if the rebuilder attempted to switch parts without me knowing

[754]

It could be on from before but with different pistons.
 Got a strong fashlite? Get 1 and 4 plugs out, turn lights off see if piston is hitting or a valve..

[Xander^]

It could be on from before but with different pistons.
 Got a strong fashlite? Get 1 and 4 plugs out, turn lights off see if piston is hitting or a valve..

It could be on from before but with different pistons.
 Got a strong fashlite? Get 1 and 4 plugs out, turn lights off see if piston is hitting or a valve..

I checker the number on the back of the engine, it has an “X” and a “7”

Also i took out the 1/4 spark plugs and noticed that the pistons do come up really really close to the bottom of that spark plug hole.. seems like your theory of the pistons smacking something is the issue.

Also noticed another ugly sound, a high pitch squeaking sound during some of the times i turn the pistons over... See attachments below

[scottly]

The K7 head I have has the same markings as yours.. Have you looked at the exhaust pipe connections where the pipes meet the head?