bertram31.com

Any idea what distributors were originally used on the B31s with 454s (1978)? My starboard engine has what looks like a Mallory with an aftermarket electronic conversion kit. The distributor for the port engine has a label on it which says "Prestolite", also electronic ignition. Everything is inside the distributor. I see no indication that these engines every had the external amplifier for the Thunderbolt system.

Thanks,

That sounds like it is an after market set up.

Any idea which, if either, of these distributors (Mallory or Prestolite) was original? The Mallory uses an electronic insert from Sierra (18-5296-2). The insert in the Prestolite looks like part # JMS-65-189 on this page: http://www.marineparts.com/mpf/mpf884.aspx .

Peter

I can tell you that our old 454's from 1975, everything was Mercruiser Thunderbolt ignition. Nothing marked Prestolite or Mallory.

Thanks. So It looks like at some point someone likely replaced the Thunderbolt systems with the Mallory and Prestolite and added the electronic conversion kits.

FWIW, when I googled the topic, I found references to use of both Mallory and Prestolite mechanical distributors on early 454s.

Peter

On Mercruisers? How old?

Here is one reference that I found for a 1977 using a Mallory.

https://forums.iboats.com/forum/engine- ... 330-please

Tony,

Based on your comments it does sound like my boat originally had the Thunderbolt system and it was replaced by the Prestolite and Mallory systems.

As of November when I put the boat in the yard, both engines were running satisfactorily so I have no immediate plan to change the ignition systems.

I have noted the following, hopefully minor, issues:

- The port engine runs at 140 degrees while the starboard engine runs at 160 degrees. Temperatures on both engines say steady once they reach operating temperature. I have not checked to see if the gauges are accurate. The port engine has a new heat exchanger which might account for the difference. (Interestingly, I have a survey on the boat from 1984 showing the engines running at 140 and 150 respectively.)

- The starboard engine needs a bit more throttle than the port engine in order to reach 3000 rpm. I plan to check the compression on both engines when the shrink wrap comes off in the spring. I also plan to check idle timing and spark advance. I have read that this might account for the difference especially since I am dealing with two different brands of distributor.

- In early fall, I had to replace the electronic conversion insert in the starboard motor (Mallory distributor).

If I do decide to replace the distributors at some point, what kind should I be using?

Thanks,

pschauss wrote:Tony,

Based on your comments it does sound like my boat originally had the Thunderbolt system and it was replaced by the Prestolite and Mallory systems.

As of November when I put the boat in the yard, both engines were running satisfactorily so I have no immediate plan to change the ignition systems.

I have noted the following, hopefully minor, issues:

- The port engine runs at 140 degrees while the starboard engine runs at 160 degrees. Temperatures on both engines say steady once they reach operating temperature. I have not checked to see if the gauges are accurate. The port engine has a new heat exchanger which might account for the difference. (Interestingly, I have a survey on the boat from 1984 showing the engines running at 140 and 150 respectively.)

- The starboard engine needs a bit more throttle than the port engine in order to reach 3000 rpm. I plan to check the compression on both engines when the shrink wrap comes off in the spring. I also plan to check idle timing and spark advance. I have read that this might account for the difference especially since I am dealing with two different brands of distributor.

- In early fall, I had to replace the electronic conversion insert in the starboard motor (Mallory distributor).

If I do decide to replace the distributors at some point, what kind should I be using?

Thanks,

Peter

The engine temps look good. I would not get too concerned over the temp difference. It could be the guage, sending unit or just that one side has a little more flow.

As far as the starboard engine. It actually could be that the throttle cable needs to be reset. They do slip and stretch over time. Ours was always off a little. In fact since our repower I am starting to notice I am having the same issue with my Cummins. I just need to check the cable adjustment.

Other that I would not look for issues. If the current ignition system is not an issue, don't go looking for one.

See now that would bug me till I knew why the temps are different.

First I'd swap the temp wires on the motors.
If temp registers the same I rule out the sensors and gauges.
If the one motors still reads warmer then you have to see which set is off.

I'd look for warmer coolant on hoses and risers, see if flow is similar.
Any crunchy lines need changing, soft ones, pinched, smaller fittings.
Check pump for wear, check or replace impeller.
Exhaust manifold inner tube clogged, heat exchanger clean and clear?
Right coolant mix...too strong pulls less heat.

Warmer and needs more throttle...I'd check timing, lube advance, make sure its working.


Your close and not a real problem...but I'd like to start looking and rule out the what it might be's.

Carl

New out of the box so to speak, our old 454's were never identical in Temp. Always varied a about 10 to 20 degrees. Never worried about them until they ran over 160. That was from 1975 when my father purchased her, until 2008 when we repowered. I don't remember how many impeller replacements, coolers cleaned etc we did but it never changed. Could have been the gauges, or the sender or just the way they ran.

Use a hand held temp gun and make sure you do not have any hot spots.