Author Topic: Engine rattle noise..Piston or Rod ? (Read 4496 times)

754 · « **on:** July 30, 2018, 04:38:35 PM »

Been a long time since I took out a rod bearing, as I recall this seems different. Cb 750

Pretty much on startup it's rattling, does not change much as it warms up.
If you up shift and work it hard or gear up high enough to lug it a bit, sound goes away.
You hear it between shifts.
Not really what I call a knock or the pinging type rattle.

So I ask if a main bearing went bad, what would it sound like .?
I am sort of thinking wrist pin or perhaps piston but need some further opinions.
Any idea ? Not looking for WAGuesses..

scottly · « **Reply #1 on:** July 30, 2018, 06:45:17 PM »

Hard to even guess without hearing it.

Does it sound worse when running at 3000 RPM in neutral, then increasing/decreasing throttle rapidly? Is this the same motor you put together right before Delores? Wasn't there something you were concerned with then?

disco · « **Reply #2 on:** July 30, 2018, 07:07:18 PM »

Frank, You need a frame kit, so you can whip the head off & take a look inside. 😜

I’ve heard good reports about the ‘weldless frame kit’. 😂

scottly · « **Reply #3 on:** July 30, 2018, 07:18:22 PM »

Quote from: disco on July 30, 2018, 07:07:18 PM

Frank, You need a frame kit, so you can whip the head off & take a look inside. 😜

That's funny!!!!

BPellerine · « **Reply #4 on:** July 30, 2018, 07:20:41 PM »

frank from what I have heard main bearings usually knock,not rattle,have you tried the old screwdriver against the engine against your ear to try to narrow it down?bill

eigenvector · « **Reply #5 on:** July 30, 2018, 07:42:32 PM »

I wore out a rod bearing on my Audi 4000, at idle it knocked - very pronounced and audible <bang bang bang bang...>. As RPMs increased the frequency went up with it but it didn't die down or go away.

754 · « **Reply #6 on:** July 30, 2018, 08:02:14 PM »

I put a wooden rod against #1, you can hear it really ticking. Even pressing your thumb against the end you can feel it.
My frame is cut, but I sold my kit, lol.
I just can't tell if I need to pull the motor, or just the top end.
I think no can ride it a bit, but hope I don't ruin a crank.
I put 500 miles on this weekend, it definitely got worse, I tank it started a few weeks back , was in the nineties temps, same this weekend. .
Worst case I have a spare motor that should be good..

MauiK3 · « **Reply #7 on:** July 30, 2018, 08:35:04 PM »

At this point I’d think about what’s spreading around the engine. Check the oil pan to see what’s in there

754 · « **Reply #8 on:** July 30, 2018, 08:41:58 PM »

It sounds like really loose tappets, or a lot like that but only from #1.

Might drop the filter and check what's piling up in there..
It only really became a concern on Friday night, but that was 500 miles ago. At highway speed in 90 plus temps. Hey its just a parts bike anyway..

PeWe · « **Reply #9 on:** July 31, 2018, 12:53:15 AM »

Time for a spare engine. There are tons of cheap running old engines on the scrap yards over there, right?

Investigate the defective one while having a running bike.
I’ll soon have 2 running bikes, my modified K6 -76 and almost stock K2 -75 still not assembled.

I have an old K1 bottom of unknown status except some rods will not move that easy. This will be a spare engine using old parts I have.

Jerry Rxman Griffin aka MuthaF'er · « **Reply #10 on:** July 31, 2018, 09:31:37 AM »

Once you pull the top end to check, the bottom will be much lighter if you don't find anything topside.

754 · « **Reply #11 on:** July 31, 2018, 10:11:18 AM »

That's what I was thinking.
Now I am wondering if the piston is touching head, that would mean rod bearing gone.

When I put it together for Dolores, I could not use the new pistons I had for it, so I picked through two set am and swapped a few wrist pins.
No idea of bottom end condition, but it has 49, 000 miles on it.

So it has to come apart, or swap motors.

Nik-bot · « **Reply #12 on:** July 31, 2018, 11:14:44 AM »

Quote from: 754 on July 30, 2018, 04:38:35 PM

...So I ask if a main bearing went bad, what would it sound like .?

it would sound like this:.

Edit: if it is spun rod bearing, sorry..

754 · « **Reply #13 on:** July 31, 2018, 11:41:30 AM »

Yeah that was how my rod sounded when it went, except I was 375 miles from home and rode it home, when I got 50 miles out there was no throttle opening where it would not knock.. scratch one crank.

Just talked to an engine builder, Goldammer. By what I said and he told me, it's a bad piston..
So top end will come off soon..

bwaller · « **Reply #14 on:** July 31, 2018, 11:51:50 AM »

Frank, a big end will knock. If you juuuuust barely (quickly)crack the throttle off idle it'll be pronounced enough to tell.

Tim2005 · « **Reply #15 on:** July 31, 2018, 01:55:13 PM »

Frank, have you got an oil pressure gauge? I'd expect the pressure to be well down, especially when hot, if there is a main or rod bearing going

754 · « **Reply #16 on:** July 31, 2018, 02:06:34 PM »

No , but after my talk with the engine builder, I am sure its a Piston problem.

Tim2005 · « **Reply #17 on:** July 31, 2018, 02:16:47 PM »

AOK. Post up if you need an odd piston, if I haven't got one no doubt someone else will have.

BPellerine · « **Reply #18 on:** July 31, 2018, 02:38:22 PM »

I dont think it would still be running if it was a big end bearing,with all the heat we have been having and the amount of miles you put on it,just my thought.bill

754 · « **Reply #19 on:** July 31, 2018, 03:16:55 PM »

I should have all the stock parts and gaskets.. thanks.

754 · « **Reply #20 on:** August 07, 2018, 04:05:42 PM »

Well it ate the cam I put in last Sept m brand new in the box Andrew's A grind. Faaacccçkkkk.

So I came back with a brand new plan..
F or K someone asks... And I say, all of the above..
Has anyone every seen an oil guage as big as this honking thing ?

kmb69 · « **Reply #21 on:** August 07, 2018, 04:56:14 PM »

Quote from: 754 on August 07, 2018, 04:05:42 PM

Well it ate the cam I put in last Sept m brand new in the box Andrew's A grind. Faaacccçkkkk.
.....

ALWAYS gotta check that top end oiling while you got'em down!

754 · « **Reply #22 on:** August 07, 2018, 05:17:19 PM »

It had lots of oil, when I opened it..
And The rockers and cradles were only put on a month before that, and I cleaned the whole top end..

scottly · « **Reply #23 on:** August 07, 2018, 05:39:19 PM »

Was the damage to the lobes, the bearing journals, or both?

754 · « **Reply #24 on:** August 07, 2018, 05:57:43 PM »

Lobes and rockers journals looked fine.
I suspect the oil or the valvesprings, vintage unused I think. Maybe RC.
I should have base lined them against stock springs, they may be way too strong.
I seem to remember numbers like 105 to 117 on the spring packs.

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Author Topic: Engine rattle noise..Piston or Rod ? (Read 4496 times)