355 bypass rattle buzz fixed

I fixed my rattling buzzing bypass valve by tightening up the long stem coming out of the vacuum box in the picture. It's a very easy task; take a look at the pictures for instructions. I also cleaned the bypass valve with silicone oil, I highly recommend it since dirt can seize the vlave from opening.
The Bypass valve does not have to be removed from the exhaust, it can be done with an
8mm wrench. All you have to do is remove the muffler heat shield and air boxes.
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Nice write up.

 

Good fix. Word of warning though.........don't overdo it. This is how I found mine when I started my major. Not only the shaft was bent - the lever was rubbing on the mounting bracket!
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This procedure is recommended if you have an rattling exhaust bypass valve. What happens is with age the spring in the diaphragm loses tension. By adding two or three turns, you are increasing the preload on the valve, keeping it from rattling. Be careful to add only what is needed, and no more. It is possible to add too much and prevent it from opening.

 

Looks like this is exactly the opposite of my description, who ever adjusted this valve closed the stem further instead of opening it.

 

Ronrob, a new Pierburg diaphragm should fix that right up, if you can find one.

BTW, there is some very thin insulating paper/material between the diaphragm and the "shelf" it is mounted on. Try not to lose that...I assume it is to prevent the diaphragm from getting too hot.

 

Thanks Huge; I wondered what the very thin plate was for. Put it back where it was anyway. In fact the rod straightened easily and I was able to bend the actuator plate back into line. Properly adjusted, the mechanism is (fortunately) no too stressed. The valve has not started to rattle (yet!). Funny thing, the BPV was working perfectly (without rattling) before I started to work on the car (opening at the right RPM's and no rattle).
Would be nice to know if the diaphragm is available separately though..........or even better, if somebody knows what other vehicles have them fitted as standard. I am aware that it's the heat that does them in.......

 

Ferrari F50 ;-)
:-(

 

Agreed, but I was hoping to find a donor vehicle that was a bit less exotic...............!

 

I suspected as much

 

question

i have not took one out yet but it looks like a throttle plate. does the end just cup over the ball ? and if so can't you snap it off at the botton end and then just turn it down without removing the top of it?

 

nope!

 

+1....doesn't want to come off easily. Safer to remove the diaphragm.

 

Stupid question most likely, however, assuming the rod is a right hand thread, top and bottom, do you turn the head of the valve clockwise or counter-clockwise, 2-3 turns. Seems to me that it should be clockwise.

 

counter clock wise, the rod should get a bit longer.

 

Fellow Rattle-ees: Well I finally got enough time to tackle the bypass rattle in my 355. I followed the advice provided through this thread. Thanks to the detail provided by several thread participants, the job went very well. I only adjusted the valve two full turns, and walla, rattle gone.

Thanks to all that posted here.

Rattle-free in Vancouver

 

Lucky you!

 

Congrats Gary!
I look forward to meeting you Father's Day weekend in North Van at the Italian Car Show at the Waterfront Park adjacent to the Lonsdale Quay Market. Are you a member of the FCA? There will be a dinner the night before...great fun, I will be bringing a contingent of FCA members from the Seattle are up on the Friday before the weekend.

 

Finally got around to doing this...it worked!!! No more annoying rattle. Thanks so much. Only thing is that isulating paper/ceramic thing basically broke in pieces and was turning to dust. Got back in as much as I could. Can it be replaced?

 

Great write up. The dealer always thinks these need to be replaced when they rattle, when clearly the adjusting screw is there for a reason.

On this same topic, I started to wonder what exactly is inside one of these that makes it so expensive, and started to look into the cross referencing to see if the are in fact other cars that use this.

Stay tuned. I've already found an exact valve replacement. I also took one apart to see if the valve could be rebuilt. I'm glad I kept my old bypass valve when I was bent over by my local dealer for a new one several years ago. Most likely I'll be able to rebulid an old valve for under 10 bucks, but I'll try it and test it out on mine and report back.

I'll start a new thread in the coming days and post some pictures.

 

Great, anything that can save us money nowadays helps.

 

Just curious what other car uses the same exact valve and what the cost is. Too often we find the same exact part is available elsewhere for a fraction of the cost. That little horsey costs lots of money when it's on a part.

 

Great stuff Mark. Looking forward to your next report!

 

Great info Mark. I am sure the diaphram can probably be sourced. But the main failure point is the bushing/bearing on the valve itself. "JH355" has experimented with rebuilding them by removing and machining a new bushing/bearing end cap. As I recall it is welded in place, so takes a bit of effort to remove and install. And he did some trial and error to get the fit exactly correct. I believe his first attempt the valve worked fine, but as it heated up, it stuck open (from expansion of the bearing surface). He removed it and took a couple thousands off (I believe) and then it was perfect.

 

I must get around to giving this a try, my valve has started to rattle more and more, now it is almost constant below the opening point.

Hope to get some time this weekend to do this... I'll report back..