Rattling Sound Coming Off A Rev

I have a rattling sound that you only hear coming off a rev. You do not hear it under power.

My mechanic, who really knows his VW's, says that it sounds like the cam gear.

This is a 1915 From VS with about 8k on it. He says it could get louder or it may be fine and just stay the way it is.

Has anyone experienced anything like this and if so, what eventually happened?

Does anyone know who builds the VS engines?

Thanks!

Can't help you on who built your engine, but check the cooling fan.

Most of the aftermarket fans are so out of balance that it's only a matter of time before they completely chew up the center and give a weird noise kind of like you are describing.

It's something to check anyhow.

Before you run it too much more! Grab the crank pulley and try to move in and out of the motor. Back and forth to the front of the car and then to the back. If you can feel the movement it has too much. What it sounds like is too much end play. This will cause a rattle sound, almost like a rod going bad as you come off a rev. I personaly have never heard a cam gear rattle.

Long story short, don't drive it until you find out what the noise is, as it might still be repairable right now.

Discribe the rattle sound...high tin pitch, deep rattle tone.

I don't know how to describe it. After I let off the rev it is there for about 1 second. My mechanic listened with a stethoscope and it's coming from the cam gear area and that's what he thinks it is. He Says that he has heard this cam gear sound in other cars.

The really odd thing is that I never heard it until they did this last work on it. They are great VW mechanics and I trust them, but it occurred after thy did the following;

Installed solid 1.25:1 rockers
Installed mid engine mount
Installed camber compensator

The sound isn't coming from the valve train area and the other items wouldn't cause this noise.

Is it possible that the engine mount or camber compensator is just making the noise louder, making the sound resonate, and so I'm just now noticing it?

Cole

Look at the crank pulley anyway, as suggested by Kevin. You can check this yourself. If it is loose it will rattle when unloaded.

Is the "mid engine mount" made of Urethane? If so, it transmits a LOT more noise made by the engine and that may be what you're hearing. I'm not a big fan of urethane engine mounts, mostly for their increased levels of noise, but they also tend to fracture under high stress.

Also, what is your "mid engine mount", where is it installed and why did you install it?

Also, if your guy found it near the cam gear with an automotive stethoscope, it may simply be sloppy oil pump gears, since the pump sits right in front of the cam gear.

Might also be the flywheel...and that can get ugly.

Most likely it is going to be endplay, start out by checking the pulley like I earlier stated.

As for the up grades you did, the camber comp. and the mid mount would not cause your sound, however if they did not set the rocker are geometry back up you could be hearing a valve lash noise. Basicaly if the rocker arms are over traveling and hanging up a little it could cause a slight rattle noise that you would hear thru the cam gear area. If they are hanging up it is causing the lifters to slap the cam. This is also not good for the solid lifters as they will fail, and then your in for a big repair bill.

The mid-mount is steel, bolted to the tranny and has two urethane bumpers. I installed it because I tore the fro t mounts in less than 7,000 miles

Cole-have you done any changes to your push-rods? Or, should you have? How about your valve springs? What kind of fuel pump do you have?

No changes to push rods, valve springs or fuel pump.

Because the noise started at this servicing, it has to be related to what was done or what was done made the noise noticeable.

I don't believe in coincidences!

Cole

I was just wondering what "interface", if any, the new rockers/assy might have with the pushrods?
SS
(I reference this article: http://www.aircooled.net/gnrlsite/resource/articles/mods.htm Scroll down to "Engine and Transmission Modifications" and keep going down to Install Ratio Rockers) Hey only troubleshooting here; perhaps one route to take in eliminating your problem-good luck!)

I wonder if the rocker arm shaft(s) has the proper stack-up of spacers and was torqued down properly? If one's just a tad loose it'll make a sound similar to that, too.

FWIW - also check the alternator strap, the big circular clamp that secures the alternator to the alternator/oil-fill stand. If this is loose, or broken, the doghouse will move back and forth as the cooling fan spools up. This will cause the fan to rub against the doghouse and creating a rattling sound.

could be the gland nut inside the fan is loose. mine did just this and it started out as a faint rattle on decel but as it slowly rounded the hole out it got louder.

Check the fan. Really.

Really.

Seriously.

Totally.

try the pulley, enough shims in there?

My pulley nut was done up nice and tight but the pulley halves still had a gap....noisy as hell !

Sounds like an alternator pulley issue.

Pull the fan belt and give it a few revs, find out if the rattle is still there or not?

Easy Peasy.

If it is . . . well . . .

Urrr Whats up .. here Ya left Mr Thompson hanging..


Im thinking its the rockers and they have hurt his cam..

If he has a lose fan he can hold the pully and move the gland nut or fan a (quick discovery)

if a stethascope centered the sound in the cam gear ares I'd say rockers have done something..

I would try what TC recommends first and maybe question whether you're using a toothed-belt. sometimes they can tend to rattle like that.


Soooooooooooooooooooooo................What's happenin??

No play in the fan.

No toothed belt.

My mechanic listened with a stethoscope and he thinks it's coming from the cam gear.

It's quiet under power and loud at Idle, when something isn't under tension.

Not sure where to go from here.

We had what sounds like the same issue (sounds almost like a bad valve adjustment but from the center of the case) and when I took it to Roland (V/S engine builder) he said there had been a few issues with cam gears. Roland replaced it with one with square cut gears (his recommendation that I agreed with) and issue solved. Good guy to work with.....
http://rasconmotorsports.publishpath.com/

I often wonder If i should have put straight cut gear in the Milage motor They did do that on the hot Vw engine ..But so far so good..

i do wish rason was on the east coast I have more big ideas.

Not a bad idea but ussaly very expencive..

Cole:

From the sound of things, you may want to consider hanging up the tires for this season and having someone pull the engine to see what's going on with the cam gear. Could be that the rivets are loose ( It's riveted to the cam shaft) and it's rattling.

Anyway, the only way to see what's going on is to pull the engine and take it all apart, down to the split case. BUMMAH!

Of course, the other alternative is to spring for MEGABUCKS and install a new engine, getting just what you want.

Well, I'm about to find the source of the rattle. It's gotten so loud that I'm having my mechanic crack the case. Like Gordon, he suspects the cam gear has come loose.

The good news is that I'll find and solve the problem. The bad news is that I've only got 7,500 miles on the engine!

Anyone know what type of warranty a VS motor has?

I suggest you give KIRK a call. He's great at taking care of their customers. He's usually there until about noon on Saturdays.

Well, it was the cam gear coming loose. Replaced it with a mild cam and bolt on gear.

Lots of trouble and expense for that little defect! But glad I caught it before any real trouble occured.

Cole,
Not sure if you've already covered this but;
Was the cam a stock rivited cam? Was it a VW Mexico cam?
If it was aftermarket w/bolt on gear, what failed? Did the bolts came loose or did the Alum gear deteriorate?

Greg

It was a stock, riveted cam. Unfortunately that's all I know.

If you got 1.25 rockers installed you have to runn chromaly pushrods set a 0 lash your stock aluminum pushrods cant handel the pressure and bend I know for a fact you have a bolt on cam gear if you bolts came loose you would know complete engine failure and a constant noise it has to be you valve trane I am a vw aircooled mechanic stock and high performance if not pushrods or lash check the rocker side play ...

Cole:

A stock, riveted cam gear is pretty common. Unless one's running an aftermarket engine greater than 2,100cc's, that's probably what is in there unless you specify other to the builder. Over 95% of the time, it works just fine, although if you run stiffer valve springs and/or modern, less slippery oils and get on it a lot from a standing stop, those angled-toothed cam gears tend to stress the gear away from the shaft - that's just the physics of that setup. After a while (and especially if the rivets weren't perfectly matched to the holes and pressed just right) the rivets can over-stress and loosen and that's what happened to you. Nothing wrong with the design for a 65-hp engine for little-old-lady VW bugs, but we're stressing everything in these engines more than they were designed for.

The bolted-on version cam gear with stock-style angled teeth is somewhat stronger just by design and they tend to last and last. The next step up, for those guys with huge engines doing dragstrip racing is to go with straight-toothed cam gears which tend to spin the gear straight, rather than force it away from the shaft and torque everything apart, but those gears tend to make an unmistakable "whining" sound. Some people (like TC and me) love that sound, some don't.

Anyway, I think once you get it all back together it should be bullet-proof. Ask your builder if it has double valve springs or single HD springs. A 1915 doesn't need a dual spring set-up, and going to mild HD singles will introduce a bit less stress on the gears as well.

Hope this helps....gn

That was great info Gordon, thanks. I don't understand why slippery oil is a factor though?

Yes, it's got heavy springs in it and my mechanic said that's what did it. When he first heard the sound a few months ago, he guessed the cam gear right off.

Cole

Modern oils have less zinc and phosphorus and are inherently less "slippery" than the old oils. Hence, they cause more friction and drag on the cam lobes and take more force to turn the cam gear, especially at start-up. If it takes more force to turn it, then, with angled gear teeth there is more force trying to pry the gear away from the riveted-on shaft.