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Mechanical, Electrical? Odd High RPM Noises. (Conclusion?)
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Mechanical, Electrical? Odd High RPM Noises. (Conclusion?)
First noticed on a couple of test passes. Sounded like a misfire once past 5000-5500 RPM.
I guessed plug wires as I've had this set of Taylors for a while and I knew that at least one of the plug boots had gone south. I hadn't bothered with a replacement as I wasn't racing and didn't have to rev the car.
But, I did rev it and the "misfire" worked it's way lower into the RPM range.
Pulled the valve covers, rolled the engine over by hand and checked each cylinder for loose valve train bits and had a look to see if there was a (another {long story and I think unrelated}) broken spring. Everything looked OK.
So here's the scoop. Hard or soft, bringing the engine to north of 3500 starts to brings what sounds like a cross between a loose rocker arm or detonation in the worst way.
Can't see detonation unless the advance bushing has disappeared entirely. But, did a test this evening with the vacuum advance removed and with the additional 10 degrees or so of advance removed, the sounds and symptoms are unchanged.
Seeing as all of the valve train parts were intact when checked at rest, one of my thoughts is that a lifter is going away and the stress at high RPM has it going flat.
Of note, is that inspection with a stethoscope revealed nothing distinct despite there being what sounds like one cylinder in distress. Rocker/lifter/spring or maybe a rod? The sound isn't like any rod knock I've heard before. It doesn't even sound like a valve.
I'm sort of at a loss.
If the timing chain had stretched, what would that sound like and would it produce this sort of "misfire sound" I experiencing?
For the record, I don't believe it's ignition related as what I have is pretty solid. It's sounds too mechanical to be ignition.
I've replaced the plug wires.
Anyway, I've posted as much info as I could. Hope someone reads through it and has an "aha" moment.
Last edited by skinny z; 10-24-2017 at 03:20 PM.
Reason: Speel check
I can't say I disagree.
What is surprising to me though is that I've had a failure prior to this. The Comp 26918 springs have proven to be reliable performers in several engines of this spec and in particular, this engine. The mileage on this set of springs isn't a third of a previous set that when the heads were taken apart for inspection (and resale), the springs were still within spec. That said, it's entirely likely that I've reached the life cycle limit of this set of springs and replacements are necessary.
Short of disassembling the top end and checking for damaged roller rockers, bent push rods, another visual of the springs (or perhaps removing them depending on my time crunch), unreasonable leak down of the lifters (which I had experienced with a previous set of hydraulic rollers) or worst case, wiped out guides, even though I've addressed the valve train geometry to within an inch (or shall I say the tiniest fractions of an inch) of it's life, I can see where replacements may be required.
Thanks for the input. I always nice to have a sounding board like this forum.
Maybe you could rig up some sort of a real seat-of-the-pants spring tester out of a spring compressor... just see how much force it takes to mash down each one. Fine detail precision isn't really necessary, or absolute numbers either. If they're giving up the ghost, odds are, there'll be LOTS of variation among them, and it won't be hard to tell which ones are limp. If they're all the same then they're probably all still good and you should look elsewhere.
THAT is an excellent idea and something I'd like to try. The reality is though that I have few tools in my new shop that would lend themselves to such an apparatus. Any suggestions in that regard?
What I am planning (sort of), is to take my current running springs along with a batch removed from a previous project and take them to a (what I hope is friendly) machine shop and test the whole lot. That will give me some insight into what I'm currently using and those which I've shelved away.
As a way of a an update, when running through my examination of the valvetrain I found everything as I suspected. Nothing strange or unusual. With one exception. I found one polylock that was split. Now that may be nothing significant in and of itself and I've never personally had this kind of occurence, but that split nut may be the same valve that offered up the broken spring earlier. That may only point to the fact that it's been through trouble previously but it may also be an indication of something more.
At any rate, once things die down around here, I'll pull all of the bits off of the engine and drudge on down to the local machine shop for some analysis. Unless of course one of the more erudite members of the forum comes up with a mechanism that will allow me to home brew my own testing machinery.
Again, as always, thanks for listening.
Or the truth may come out:
I have the Comp short travel lifter. Now this update from Comp. Although I may not be in the following descriptor, I certainly am in the extreme use category.
Certain engines respond better to a light lifter pre-load because it recovers more quickly from any bad harmonics in the valve train. Others work better with a heavy pre-load because oil volume is reduced under the plunger, which increases lifter stiffness. COMP Cams® Short Travel Hydraulic Roller Lifters let you have the advantages of both light pre-load and reduced oil volume, producing the most stable and highest-revving hydraulic lifter available. COMP® now offers an XD version of these lifters that features a heavy-duty tool steel pushrod seat. This adds strength and durability in Xtreme Duty applications such as turbo drag cars and offshore powerboats.
This kind of **** pisses me off. I buy the part so as to beat the **** out of them only to find that they're not designed for for a **** kicking application.
Damn!
If I survive past the valve spring testing, it points to the lifter and that makes sense from a historical perspective. The 26918 spring has never failed me but the short travel lifters are a new endeavor.
Time will tell.
You can use the lever type of on-the-head valve spring removal tool to "feel" for weak springs. It does not have a gauge - you will just have gauge by feel. Just find some means of covering the "C" opening so that you push down on the valve stem and cannot pop the retainer free - dropping a valve. If you want more precise, they do make on-the-head valve spring testers. Or you might find a way of rigging up something like in the 2nd pic.
As the driving season comes to an end in these parts of the world, the Camaro gets put away.
I'll use the off-season to address this and a hundred other things that have accumulated over the summer. Most likely is the removal of all of the springs and having them actually tested. I'd like some values. And as I mentioned, I have another set that I'm curious about as well.
In the meantime, I've continued to drive the car (it's serving as a daily at the moment) although RPMs don't exceed 3000. Even then, there is the obvious (but not alarming) clatter of valve train noise. Seems confined to a single cylinder but that's difficult to determine.
An update of sorts.
Changed the oil and found a fragment of metal stuck to the drain plug. It appears to be a portion of a small gear. Not unlike what you might see on a distributor or camshaft.
I haven't pulled the distributor to examine it (working out of town) but I have my suspicions.
Further to that, and this is something that caught my attention earlier, the inside of the distributor cap has material removed on a plane parallel to the rotor (like it was turned on a lathe). Just half the circumference though. This was what I figured to be the result of the cap not being on straight at one time or another. Now I'm not so sure.
That this misfire has moved lower in the rev range over a very short period of time has me questioning the valve spring failure. That and that the history of these springs has been nothing less than heroic. I can cite several examples. Somehow an overall failure seems unlikely (but of course not impossible).
All of that said, I hope to have the opportunity to dig into it next time I'm back in the shop. Check the distributor and the cam gear. If they check out OK, (although I'm somewhat certain the fragment I found in the oil is part of the distributor gear), I'll pull the springs and have them checked for spec.
Last edited by skinny z; 10-15-2017 at 09:52 PM.
Reason: Clarity and additional information
Having pulled the distributor, the gear is intact as is the rest of the unit. It's difficult to get a good look at the cam gear but from the size of the fragment relative to the gear, it doesn't look like that would be the source either.
My guess is that it's a piece of a cam lobe. I had a broken spring (as mentioned earlier) and that could have pounded a chunk off.
A few pictures:
What shape are your plug wires in? I have seen MSD ignitions do some pretty weird crap between #5 and #7 plug wires arcing to each other. Arcing between those two plug wires can cause preignition on the #7 cylinder while the rest continue to fire as advertised.
I had suspected the plug wires and have since replaced them. As before I'm using Taylor 8mm. Carefully routed and loomed. Misfire still.
I was bench racing with a car buddy the other day and the thought of the spark plugs, although relatively new and appearing to be in good shape, might be gapped a little on the far side. I can't recall exactly but I think I'm at least .045". That is on the recommendation of MSD. Sometime this week I'd like to do a leak down test and the plugs will be out then. I think I'll tighten them up to .040".
Still, I'm beginning to believe this misfire has a mechanical origin. Problem is, I can't do much about as the Camaro is serving as my daily driver and I can't afford to have it disassembled for examination. At least not until I service my truck (or replace it).
In the meantime, I'll continue to speculate and check on the simple things.
Re: Mechanical, Electrical? Odd High RPM Noises.(Conclusion?)
A leak down test shows the best cylinders at 16% !
The worst are nearly 50% loss.
Despite possible procedural errors, I think it's fair to say this engine is toast.
And I think it's also fair to say, this is the cause of the misfire.
Re: Mechanical, Electrical? Odd High RPM Noises.(Conclusion?)
Originally Posted by skinny z
A leak down test shows the best cylinders at 16% !
The worst are nearly 50% loss.
Despite possible procedural errors, I think it's fair to say this engine is toast.
And I think it's also fair to say, this is the cause of the misfire.
Hate to hear this buddy, the good news is you now get to do a refresh on the engine with upgrades you've been wanting to do anyway.
Re: Mechanical, Electrical? Odd High RPM Noises. (Conclusion?)
I suppose there IS an upside.
I had really wanted to test this new combination of ported heads, bigger cam and higher stall converter at the track but circumstances conspired against me and I wasn't able to get out at all.
Now I'm thinking about another step function change and building with more cubic inches. I'd hate to just go sideways with an overbore and bearings although that is the budget friendly route. Still, moving up to 385 CID and a properly spec'd cam might get me into the 11's.
No rush at this point. The new season is about 6 months away.
10-02-2017, 09:49 PM
