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AQ 130 valves have "snapping" noise

J

joe_merchant

Regular Contributor
I've rebuilt a AQ130C and started it up. There's a noise in the valve train that isn't there in my other operating engine. When I turn it over by hand, each valve/pushrod makes a snapping noise just before it reaches it's full travel on the opening sequence. This is a new cam and new lifters but the old pushrods. Since these are solid lifters, they are all adjusted at the rocker arms. I also put the old cam back in with the same results. The pushrods all appear to be in good shape and they are installed correctly.

My only guess at this point is that the machine shop may have milled the head too much. I'll try it with 2 head gaskets to test that theory. Anyone have any other ideas?
 
i would not replace the head gasket. regardless how much the machine shop milled the head, you would be able to compensate for that in your valve adjustment. what i would check for, ......is spring bind. that is where the valve springs are compressed to the maximum, they then become solid.....(maybe a snapping noise...??) were the valve springs replaced or shimmed ??
 
The springs are the originals and don't appear to have been shimmed. I have the springs from another head and they appear to be the same. I'll put the cam back in this weekend and watch closely as I turn it over by hand and see if I can pinpoint the exact source of the noise. Before I do that, would it be a good idea to put the valve spring compressor on a few of them to see if I can duplicate the sound that way?

Even if I do isolate the noise as springs binding, what would be the resolution?
 
if the vavle spring is bindinging...then the spring would have to be replaced with a spring that has the same tension, but has a smaller spring thickness. your machinest would be able to help with that.
....also, after thinking about this some more.....weak springs can also be doing the same thing. by not keeping constant spring tension on the cam follower, this would allow the follower to "lift" off the cam, causing a slapping noise.
valve springs a very inexpensive. order some from "comp cams"......cheap insurance and a good performance investment. avoid the volvo venta springs.
 
crankbait said:
....also, after thinking about this some more.....weak springs can also be doing the same thing. by not keeping constant spring tension on the cam follower, this would allow the follower to "lift" off the cam, causing a slapping noise.
Click to expand...
I agree with your previous assessments with exception to the above.
This would not normally occur unless the RPM was excessive.
Yes/No???

Joe, what procedure are you using to set the valve stem to rocker arm clearance?

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I'm using the procedure in the Volvo Penta manual. The page is attached below.

I've only run the engine for about half hour and that's on the engine stand so no excessive RPM's. You can clearly hear the noise while turning it over by hand.
 

Attachments

  • valveadjustment.pdf
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are you sure that you are hearing a snap coming from the valve train and not a spark from the ignition ?? bad wire, etc...??
 
Just put the engine part way back togther to look closer. The valves are not compressed to the maximum. After listening closer, it seem that the noise is actually coming from inside the engine and that wouold indicate it's when the pushrods are shifting around in the pocket of the lifter. I can feel the "click" on individual pushrods. I've looked at the pushrod ends and they don't seem to have expanded. I believe my next step is to take it apart again and check to see how each pushrod fits into the socket of the lifter. Yes/no. other ideas?
 
a solid cam, with solid lifters, is supposed to make a certain amount noise. that is normal. my concern, is that you are setting the valve lash on the loose side. what lash are you setting them at ? (how many thousands)
 
0.020 but the "snap" isn't occuring while it's taking up slack. It's toward the end of the valvetrain travel, just before the valve is fully open.

I understand about solid lifters and the valve train noise. I'm also familiar with the whine from steel crank and cam gears. There is an operating AQ130D in the boat that runs without this noise, that's why I'm questioning it.
 
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Joe, what if you were to loosen each rocker arm while you checked again.
Or perhaps loosen all of them and check again!

Any suspicions of the fuel pump arm as it's cam operates it?

Is this in sync with the crankshaft rotation, or is it in sync with camshaft rotation?

How many times will you hear this during one crankshaft revolution?
How many times will you hear this during one camshaft revolution?

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Right now, the distributor and fuel pump are removed. The noise does not occur when the head is removed. When I was trying this yesterday, I had not tightened up the pushrods so some were pretty loose. I'm going to try this one cylinder at a time by removing all the pushrods except those for a single cylinder and pay particular attention to just what you're saying about exactly when it's happening and if it's consistent with both intake and exhaust valves.

I'm going to try this one cylinder at a time by removing all the pushrods except those for a single cylinder and see exactly when it's doing this. I'll also inspect the pushrods more carefully to verify they're all the same length, straight, and that the ends are in good shape.

I see what you're saying about ruling out everything except the valve train and think I've done that but will keep looking for anything else that it might be.
 
I've tried everything I can think of. Checked all the pushrods and they're all in good shape without any scratch marks, they're all straight and true and all the same length. Turned it over with the pushrods in just one cylinder at a time and they all still have the snapping noise. The noise accurs at initial compression and then about half way down.

Had a cracked head sitting in the garage so tried that one with the exact same results. That tells me there is nothing wrong with the valve springs or keepers. Disassembled the rocker assembly and cleaned it up a bit but that didn't change anything.

It's still a mystery to me and maybe normal so guess I'll just leve with it.
 
joe....before you throw in the towel.....sometimes, it's best to step back, and have another person that has hands on engine repair experience, stop by and listen. what you may think is an unusual noise, may be normal, or an item that needs immediate attention. it can't hurt. if you were in sacramento, i'd be more than happy to come by.
 
Thank you very much for the offer and you're welcome to stop by if you're in the area! The engine is a spare so there is no great hurry for it.

The engine in the boat is still running fine but compression is a little low. I'm rebuilding this one as an eventual replacement. Thought it would be easier to do this without any time pressure and have it ready instead of stressing when the old one gives out.
 
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