|
Sponsored Links (Register now to hide all advertisements) |
|
|
Thread Tools | Display Modes |
09-29-2015, 04:57 AM | #1 |
Senior Member
Join Date: May 2010
Location: Napier, New Zealand
Posts: 2,001
|
Vexing problem.
I've been trying to find a knocking noise which is driving me nuts. I rebuilt my C59a engine about 9 months ago and gave it a hone, new rings, rod and main bearings, new valve guides and faced the valves. I had the heads milled to give me 50thou piston/chamber clearance, but otherwise is stock. It runs like a champ, but has an intermittent knocking noise which I am chasing. Using a length of rubber hose as a stethoscope, I determined the valves on #5 are very noisy. All other cylinders are very quiet in the valve area, but putting the hose on the valve area on #5 is incredible. Compression is same as all the other cylinders.
I pulled the head, had a visual, checked the lash on both, all seemed OK, retainers both in the correct place. I pulled both valves, they looked OK, springs OK, guides OK, pulled the Isky lifters, OK. I rummaged through my parts and found two solid lifters the needed length and installed them, just in case there was something wrong I couldn't see. Reassembled everything, taking care to make sure the retainers were located properly, and the lash was within spec. Fired it up, dang! That noise is still there! I've run out of ideas, so I'm looking for inspiration here. I know sometimes it's hard to see the wood for the trees. PS: I should add, the stethoscope test indicated the noise coming from above the spark plug, so I ruled out piston knock. |
09-29-2015, 06:01 AM | #2 |
Member Emeritus
Join Date: May 2010
Location: Fitzgerald, Georgia
Posts: 2,204
|
Re: Vexing problem.
This can be a tough diagnosis request. The first thing I try to do is determine if the noise changes when the cylinder is grounded(no spark). If so, it points me toward the piston/rod area. If no results are obtained from that test I try to determine if the noise is at piston speed or at valve speed intervals. With some rigorous intelligence you will figure this out because the valves(obviously) move at only half that of the piston.
As an aside, if the noise comes and goes don't discount the fuelpump as a contributor. |
Sponsored Links (Register now to hide all advertisements) |
|
09-29-2015, 06:21 AM | #3 |
Senior Member
Join Date: Aug 2012
Location: Perth, Western Australia
Posts: 2,687
|
Re: Vexing problem.
What does your vacuum gauge say?
__________________
"Came too close to dying to stop living now!" |
09-29-2015, 07:40 AM | #4 |
Senior Member
Join Date: Jul 2010
Posts: 2,593
|
Re: Vexing problem.
To add to above,
The exhaust valve in #5 is it definitely not hitting the spark plug? Martin. |
09-29-2015, 07:57 AM | #5 |
Senior Member
Join Date: May 2010
Location: Northeast Pennsylvania
Posts: 1,582
|
Re: Vexing problem.
You milled the heads for 0.050 piston clearance, but did you look at valve pocket clearance?
|
09-29-2015, 11:12 AM | #6 |
Senior Member
Join Date: May 2010
Location: middle of Iowa
Posts: 632
|
Re: Vexing problem.
Sponsored Links (Register now to hide all advertisements)
|
09-29-2015, 11:59 AM | #7 |
Senior Member
Join Date: Jul 2014
Location: Iowa
Posts: 1,634
|
Re: Vexing problem.
If the noise is confined to just one cylinder, it seems unlikely that milling of the head is at fault. The noise could be a broken piston ring, or a loose piston (wrist) pin. If the plug wire is disconnected, and the noise changes or goes away, it will narrow down the possible problems.
|
09-29-2015, 02:14 PM | #8 |
Senior Member
Join Date: May 2010
Location: Napier, New Zealand
Posts: 2,001
|
Re: Vexing problem.
I foil balled the valves when I did the heads. Also, there's no visual of any interference. No carbon build-up. JWL, no change when the lead is grounded, and the stethoscope test gives a quiet fuel pump, and very noisy valve area on #5, also a bit on #6 but I think that's spill-over noise from #5. Talkwrench, I have a vauum gauge, I'll have to make up a fitting so I can use it.
|
09-29-2015, 02:23 PM | #9 |
Senior Member
Join Date: May 2010
Location: Oregon City, Oregon
Posts: 208
|
Re: Vexing problem.
Could be a lose valve seat
Or lose guide sliding up and down. Just a thought... |
09-29-2015, 03:44 PM | #10 |
Member
Join Date: May 2010
Location: Federal Way, WA
Posts: 95
|
Re: Vexing problem.
What RPM's are most noisy?? Any difference warm v.s. cold?? Metallic click sound or somewhat subdued??
FWIW, I had a noise that nobody I asked at a Bonneville meet could figure out and I pulled the manifold, checked the valve train, found nothing wrong. Turned out to be a broken wrist pin. Flat32 |
09-29-2015, 04:08 PM | #11 |
Senior Member
Join Date: May 2010
Location: Powell, TN
Posts: 2,503
|
Re: Vexing problem.
valves do not usually knock. Loose flywheels may, thrust surface off a main may cause a knock..............you really have to be careful about milling heads and valve clearance, I know from sad experience years ago.
|
09-29-2015, 04:22 PM | #12 | |
Senior Member
Join Date: May 2010
Location: Napier, New Zealand
Posts: 2,001
|
Re: Vexing problem.
Quote:
|
|
09-29-2015, 07:24 PM | #13 |
Senior Member
Join Date: May 2010
Location: N.E.Ohio
Posts: 222
|
Re: Vexing problem.
Could be a broken or missing circlip and wrist pin has moved out to meet the cylinder.
|
09-30-2015, 02:41 AM | #14 |
Senior Member
Join Date: May 2010
Location: Oamaru, New Zealand
Posts: 416
|
Re: Vexing problem.
I came across a similar knock on a 38 coupe once....after a lot of headscratching it turned out to be the starter pinion. It was missing the little spring and pin, and the pinion at certain revs, would move forward and contact the flywheel ring gear.
|
Thread Tools | |
Display Modes | |
|
|
Sponsored Links (Register now to hide all advertisements) |
|