1988 7.4 Bravo One with a rattle noise

[catman4u]

Just some of the history first. No noise before I pulled engine out to repair exhaust leak at wye connection and replace cyl head due to erosion of exhaust manifold to head and from crack in manifold. While engine was out. Replaced exhaust flappers. Put everything back together about two yrs later. Noticed a rattle in to drive upper to gamble area. Pulled drive and installed new gamble and new joints from mercruiser. Original parts lasted this long I'm going back with the same. Noise is still there. I have been looking here for the answers and I've heard about the flappers causing possible the same noise. Any thoughts? I've used an alignment tool also to verify alignment. I was going to run this next without drive hooked up to verify but just didn't want to do if I didn't have to. Those damn bravos are getting heavy to pick.

 

[dubs283]

Re: 1988 7.4 Bravo One with a rattle noise

sometimes if the firing order is incorrect or the timing/idle is off it will cause the upper gearset on bravo drives to rattle - i have heard this happen on inboards when the idle is set too low or the enigne needs a tune-up

check #5 and #7 for firing order, and timing/idle

the new flappers shouldn't be making any noise, the are coated in rubber

 

[04fxdwgi]

Re: 1988 7.4 Bravo One with a rattle noise

The flappers can make a rattling sound at or just above idle. Any thin metal covers can make a rattling sound, also, and can drive one nuts trying to find it. The noises can seem to come from nowhere near the source. Check to see if the flywheel cover is bolted tightly to the bell housing. If loose, they can rattle a bit at certain RPM's and sound like the noise is coming from the transom plate.

 

[tpenfield]

Re: 1988 7.4 Bravo One with a rattle noise

I often use a tube held up to my ear in order to isolate where certain sounds are coming from. If you can't isolate it, then removing the outdrive is a good approach.

 

[TilliamWe]

Re: 1988 7.4 Bravo One with a rattle noise

...Those damn bravos are getting heavy to pick.

My Bravo 3 was 153lbs. It was difficult to lift it off and on by myself, but patience and an outdrive stand would help a lot. A second person is even better!

 

[tpenfield]

Re: 1988 7.4 Bravo One with a rattle noise

Yup, a bit heavy, but I find that a 2-wheeler and a good breakfast do the trick. Just count it as your work-out for the day . . .

 

[catman4u]

Re: 1988 7.4 Bravo One with a rattle noise

Sorry about delays getting back. Diesel mechanic for a living. Didn't think about a low idle causing issue. Possible? I've played with the idle somewhat and believe its high enough by ear but will recheck with a photo tach. I haven't pulled the upper case apart yet to inspect for a broken gear. Thanks for all the responses so far. Gives me somewhere else to go look. Boat has a molded swim platform which makes the picking of the out drive a b$$ch.

 

[TilliamWe]

Re: 1988 7.4 Bravo One with a rattle noise

... Boat has a molded swim platform which makes the picking of the out drive a b$$ch.

Yeah they don't help. I found that by lowering the trailer tongue way down, (and backing the trailer up on blocks)I could use the skeg to rest it on, and pry it off a bit. Since my skeg was all corroded and scratched up, it didn't hurt anything. Maybe you could try something similiar?

 

[04fxdwgi]

Re: 1988 7.4 Bravo One with a rattle noise



This may help. I built this from a twenty buck dolly from Home Depot. Lower drive onto dolly, unbolt drive and roll it away from the stearn. No lifting involved at all. May need to raise / lower trailer tongue to get it to set right, but when done, no back pain at all. Them Bravo 1's are heavy....

I have measurements, if you want to try something like this too.

 

[MarkSee]

Re: 1988 7.4 Bravo One with a rattle noise

.. I built this from a twenty buck dolly from Home Depot. ....Them Bravo 1's are heavy....

$7.99 1,000 pound capacity dolly from Harbor Freight is what mine is based off of.

Because of the B3 in my case, the top supports I used 2 x 6 to get more surface area instead of 2 x 4.
Depending on how long the "tongue" is, very important though to either have a helper or use some blocks as counter weight on the back side or it will want to tip with the B3.

Mark

 

[Mischief Managed]

Re: 1988 7.4 Bravo One with a rattle noise

View attachment 185792

This may help. I built this from a twenty buck dolly from Home Depot. Lower drive onto dolly, unbolt drive and roll it away from the stearn. No lifting involved at all. May need to raise / lower trailer tongue to get it to set right, but when done, no back pain at all. Them Bravo 1's are heavy....

I have measurements, if you want to try something like this too.

I built a similar stand, but mine fits on top of a mechanics creeper that I already had.

 

[TilliamWe]

Re: 1988 7.4 Bravo One with a rattle noise

And I got one as a gift from Bim's Racing. Very stable, not tippy, with rubberized non-slip where the anti-ventilation plate sat. Sweet present, I must say!