air silencer base screws

[Thumpbass]

The manual for my '79 100hp says when removing the air silencer base to get to the carbs (for a carb clean/re-build) to discard the air silencer base mounting screws and to use new screws when reassembling....I'm assuming since the manual says to replace with new screws that it must be of some importance so my question is should I order the specific screws from the motor's parts list or can buy the same size screw in a similar grade/material from a hardware store?

 

[imported_lorin]

Re: air silencer base screws

This sounds pretty strange. Does anyone know why you would need new screws to hold a piece of plastic on?

 

[F_R]

Re: air silencer base screws

While I am not familiar with that particular motor, I would assume the screws probably have some sort of factory applied locking material. Could be a nylok pellet or what they call drylock...a dry form of Loctite. Whatever it is, I'll bet they have a motive in mind--to keep the screws from rattleing out and being ingested into the engine, a catastrophic event.

 

[Thumpbass]

Re: air silencer base screws

This sounds pretty strange. Does anyone know why you would need new screws to hold a piece of plastic on?

It's not the plastic air silencer cover, but the air silencer base...which is the metal piece that bolts to the front of the carbs...the plastic cover screws to the metal base.

 

[Thumpbass]

Re: air silencer base screws

While I am not familiar with that particular motor, I would assume the screws probably have some sort of factory applied locking material. Could be a nylok pellet or what they call drylock...a dry form of Loctite. Whatever it is, I'll bet they have a motive in mind--to keep the screws from rattleing out and being ingested into the engine, a catastrophic event.

the manual does say to use "OMC screw lock with new screws" when re-attaching the air silencer base. Which my next question would be; can you still get "OMC screw lock" or is there a similar product that will suffice like Loc-Tite... that's the problem wirh OEM manuals that are 30 years old.

 

[rickdb1boat]

Re: air silencer base screws

Blue Loctite will be fine....

 

[jtexas]

Re: air silencer base screws

Only reason I can think of to replace screws every time is if the torque value is high enough to stretch 'em.

 

[wormboy]

Re: air silencer base screws

Thumpbass-- i had exactly the same question! I can't imagine the torque for these is high enough to stretch them, and given that the air silencer is an open system, the reason to have it sealed so tightly to the carb's is kind of weird as well. Besides, it seems that servicing/cleaning the carb's is such a common thing you could end up going thru the bolts like going thru bait.
Really guys-- how many of you boat mechanics out there have actually replaced these bolts every time you've cleaned or rebuilt carb's, and have bothered to put lock-tite on these bolts? If these bolts are more susceptible to loosening than others on the engine, why not use lock washers?

 

[Thumpbass]

Re: air silencer base screws

assuming you do need to replace the screws, I still wonder if you can replace them with screws from the hardware store in a similar grade/material or if you need to order them from an OMC parts dealer.

 

[wormboy]

Re: air silencer base screws

all i can say is that the nearest OMC parts store for me is 40 miles away-- if they even carry those bolts-- and the hardware store is 2 miles away. The old screws-- which had no locktite on them from an engine that is 17 yrs old and has seen more than a few carb removals-- were next to the engine where I put them.
My choice was easy-- may not have been the right one, but we'll see.
good luck!

 

[imported_lorin]

Re: air silencer base screws

I have worked at a number of boat/motor dealerships, and no one has ever replaced, or even considered replacing such screws. The loctite is a fine idea.

 

[dsinger]

Re: air silencer base screws

"dont discard the air silencer base mounting screws and don t buy new screws when reassembling".... that is what it is suppose to say has to be a miss print. That all sounds really worthless to me. What manual are you using mine does not say anything like that.

 

[Thumpbass]

Re: air silencer base screws

"dont discard the air silencer base mounting screws and don t buy new screws when reassembling".... that is what it is suppose to say has to be a miss print. That all sounds really worthless to me. What manual are you using mine does not say anything like that.

It's the original Johnson Service manual for V-4 models 85,100,115,140ML79, TXL79, and TL79 (item number JM-7909). It says to use new screws on 2 different pages (the removal of carbs and re-assymbly of carbs sections). Surely can't be a misprint twice, right?

 

[jtexas]

Re: air silencer base screws

from page 3-3 of the 1979 Evinrude Service Manual, 70HP model 70973, 75HP models 75942, 75943:

...
d. Remove six screws retaining air silencer... Discard six self-locking air silencer to carburetor screws, as new screws should be used on reassembly. See Figure 3-5.

If I had a scanner, you could see Figure 3-5, with its nine large arrows pointing to the nine air silencer to carburetor screws. Doesn't say which six are self-locking.

I'm planning on reusing 'em, unless somebody here convinces me otherwise. With blue locktite.

 

[wormboy]

Re: air silencer base screws

Self-locking suggests that removal probably damages them-- the screws I removed on my 89 E150 don't seem damaged and torque down just dandy-- maybe they were replaced over the years with regular bolts.

Can anyone tell me why it is so important to have gaskets and locked screws on an already open system like an air silencer? I guess the weight and shape of the silencer makes it prone to vibration and loosening-- but why are the gaskets so important? Maybe just vibration dampening?

 

[farginicehole]

Re: air silencer base screws

I just secured a factory manual for my '89 XP150 last week. It also says to discard these air silencer base mounting screws and to use new ones when reassembling. I thought that sounded kind of weird too!

 

[wormboy]

Re: air silencer base screws

Hey farginicehole-- not to disrupt this thread-- but i saw somew older threads from you a while back; we have the same engine and have had similar troubles. i am curious about a problem youhad awhile back and what happened.
e-mail me: bkelly@emory.edu

 

[Thumpbass]

Re: air silencer base screws

Self-locking suggests that removal probably damages them-- the screws I removed on my 89 E150 don't seem damaged and torque down just dandy-- maybe they were replaced over the years with regular bolts.

Can anyone tell me why it is so important to have gaskets and locked screws on an already open system like an air silencer? I guess the weight and shape of the silencer makes it prone to vibration and loosening-- but why are the gaskets so important? Maybe just vibration dampening?

Well when I bought my boat/motor (used) the motor did not have an air silencer cover. I was green at the time because my previous motor was a '85 15hp Johnson...this was my first "big" motor. But anyway I didn't realize there was even supposed to be a cover on there until a few after I bought the boat, I cranked the motor up in the front yard and noticed fuel accumulating in the motor well. After removing the cowl and trying to find out where the fuel was coming from, I noticed fuel spilling out of the intake of the air silencer base when I was cranking the motor. There was also fuel squirting out of a small hole on the bottom right corner of the air silencer as well...so, this is where the fuel was coming from. After I got my manual in mail I realized that the motor had the air silencer cover (so I bought one)...appearently the fuel coming out of the front of the air silencer when starting is normal...the cover and gasket contains the spill and the fuel drains back into the manifold via the small hole on the bottom right corner. So to answer your question...I guess the gaket is to keep the fuel better contained between the base and cover.

If this is wrong and abnormal...someone please speak up:/

 

[jtexas]

Re: air silencer base screws

Can anyone tell me why it is so important to have gaskets and locked screws on an already open system like an air silencer?

I'm no engineer, but here's a theory:
Its called a "silencer" but I think it's about more than just noise abatement...from the position of the air intakes I'm guessing it's more about regulating the temperature of the air entering the engine.

You're screwing a plastic part to a metal part...putting a piece of cork between 'em makes sense to me.

Also the fact that it's plastic limits how much torque you can apply, so having a screw made of softer metal than the casting, with threads that deform a tiny bit in order to lock it in, makes sense too.

I'm still using blue locktite, which I noticed is recommended by the Seloc manual.

 

[wormboy]

Re: air silencer base screws

The base on these engines is metal, so there's no plastic involved. i think thumpbass is on to the purpose-- there is a drain hose from the base to the manifold, and there is always a chance of fuel running out when priming with the solenoid before turning the engine.
However, I'd hate to think that crap that can get into the silencer can get dissolved with spilled fuel and sucked directly into the manifold.......