Distributor cap/rotor replacement, questions!!

[tmh]

Many threads here about my boat not reaching expected WOT rpm, won't go into details again but nearly everyone agreed it's underperforming a bit. Working through Don's list of what to look for and today I am changing the dist cap and rotor.

OK, not an engine guy, but trying to follow manual and a couple threads here on changing out the dist cap and rotor on my 1985 Mercruiser 305 w/ thunderbolt IV. I ordered parts online and rec'd the cap, rotor and a small plastic part called "coupling" something or other.

Changed wires to new cap as per old, removed old cap. Couldn't get rotor off, but checked a thread here and learned it takes prying and heat sometimes, so I got that off. This is where i am now. here are my questions/issues.

The shaft is very rusty....does this matter and what to do about it?.

Where one of the rotor pegs contacts a small mechanism (don't know what it is, but it's the only thing in there) there is lots of rust on the top of the contact area (I think it's a contact area). What is this unit and do I replace it also while I'm in there or clean it somehow or just leave it?

Lastly, what is that small coupling part (actually, two small pieces in the bag)? Where does it go? Thx as always.

 

[tmh]

Re: Distributor cap/rotor replacement, questions!!

Oh, one more question....do i use dielectric grease anywhere when i re-install rotor/dist. cap? Thx.

 

[tmh]

Re: Distributor cap/rotor replacement, questions!!

OK, I ran out of time so I finished the job. Left all other items as-is, just new rotor and dist cap for now. I greased the shaft slightly so the new rotor would slide into place properly - still had to push hard to get it all the way on. Ran engine on muffs, no problems at low rpm so I'll take it out tomorrow and see if it helped at all. The old cap and router had plenty of corrosion, so would you think I'd pick up some performance from the change? Or is it more a PM thing if the old one was working at least to a point?

I think the "coupling" part was thrown in by the seller as a "thank you" for the purchase of tune-up parts. It's a Quicksilver Coupling Kit 22-815956A 1 which looks to be some sort of pitot tubing......no idea what it's for, any ideas? Thanks.

 

[bruceb58]

Re: Distributor cap/rotor replacement, questions!!

While you were doing all of this, did you replace the points? If not, I suggest you do. If the rotor and the cap looked that bad, I can just imagine what the points looked like. Also, you will need a dwell meter to set the point dwell and a timing light to adjust the timing after you do that.

 

[tmh]

Re: Distributor cap/rotor replacement, questions!!

Bruce, thanks for the reply. Stupid queston, but what exactly ARE "points"? How hard are they to replace? The marina DID replace plugs and set timing recently, I wonder if they checked the points? I can ask them.

Thx.

 

[cooter2506]

Re: Distributor cap/rotor replacement, questions!!

Thunderbolt IV doesnt have points. The contact area I belive you are refering to is a sensor. It reads the "pegs" of the rotor as it spins. It is part of the Thunderbolt ignition system. If it is that rusty i would change it out. possibly metal is contacting the sensor when it is turning and causing your advance to not work properly

 

[bruceb58]

Re: Distributor cap/rotor replacement, questions!!

Thunderbolt IV doesnt have points.

I missed the part where he stated Thunderbolt ignition. Yep...no points.

 

[Liberator 6]

Re: Distributor cap/rotor replacement, questions!!

The contact area I belive you are refering to is a sensor. If it is that rusty i would change it out. possibly metal is contacting the sensor when it is turning and causing your advance to not work properly

Hmm, I posed the same question but no answer. Is it called an ignition sensor, or is there another name for it? Thanks -