schwarz633
New member
I recently replaced the distributor caps and rotors on my 1989 Sea Ray 300WE with twin 5.7 Mercruiser SBC inboards. The rotors were seized onto the distributor shafts and very difficult to remove. It was necessary to crank the engine to rotate the rotors in order to be able to pry up from opposite sides. This was done with the HT lead removed from the coil (bad idea, should have been grounded). On one of the engines I observed arcing from the HT tower on the coil to both of the small studs. Upon reassembly that engine wouldn't fire, no spark. The arcing had apparently taken out either the Thunderbolt IV module or possibly the hall effect sensor in the distributor. The TB module receives the signal from the distributor and provides the timing advance based on engine RPM.
After doing some research I decided on upgrading both distributors to DUI Marine HEI mechanical advance (only) units from Performance Distributors. I liked the fact that the coil was incorporated into the cap and the installation would be clean and easy, eliminating the TB module and the coil. The only connections to the DUI distributor are +12V and the tachometer wire. The other option was the Delco EST which was ~ $100 more per distributor and not in stock.
My starboard engine is reverse rotation so I assumed that I needed a reverse rotation distributor which was +$70 for the DUI and +$300 for the EST. The only difference is that the gear of the distributor is cut in the opposite direction, both distributors turn CW.
After spending a couple of hours trying to get the reverse rotation DUI distributor to drop down into the starboard engine I discovered that my reverse rotation engine doesn't use a reverse rotation distributor. I have since found out that these marine SBC engines were produced in standard as well as reverse rotation with timing chain and timing gear versions of both.
I did however get the dead starboard engine running again using the standard rotation DUI distributor that was intended for the port standard rotation engine. The reverse rotation DUI distributor has been sent back to Performance Distributors to get converted to a standard rotation and I hope to be installing that on the port engine in the near future.
At this point I've only set the DUI distributor timing by ear, as both of the (2) digital variable advance timing lights that I have are telling me that the timing at idle was 39° advanced, with the engine starting and running normally. Performance Distributors advised me that a digital timing light won't work with the DUI distributor, something about their extended dwell period throws them off.
I recently located an old school non-digital timing light and printed out some timing tapes to attach to the harmonic balancer so I could check the full advance. The old school timing light is also telling me 39° advance at idle, it should be around 8° BTDC.
I'm absolutely sure that I'm clamping the timing light onto the #1 plug wire, been checked multiple times. And as I've said, the engine starts and runs great.
The only other thing I can think of is that the outer ring on the harmonic balancer has slipped, anyone have any experience with this happening?
Hopefully I'll gain some additional facts when I install the DUI distributor on the other engine and see what the timing lights tell me there.
Are there any other oddities that are associated with timing a reverse rotation engine?
My next step is to pull the #1 plug and do the finger over to hole thing to find the compression stroke and then stick something in there while turning it over with the crank bolt to find TDC, then see where the mark on the harmonic balancer is located.
After doing some research I decided on upgrading both distributors to DUI Marine HEI mechanical advance (only) units from Performance Distributors. I liked the fact that the coil was incorporated into the cap and the installation would be clean and easy, eliminating the TB module and the coil. The only connections to the DUI distributor are +12V and the tachometer wire. The other option was the Delco EST which was ~ $100 more per distributor and not in stock.
My starboard engine is reverse rotation so I assumed that I needed a reverse rotation distributor which was +$70 for the DUI and +$300 for the EST. The only difference is that the gear of the distributor is cut in the opposite direction, both distributors turn CW.
After spending a couple of hours trying to get the reverse rotation DUI distributor to drop down into the starboard engine I discovered that my reverse rotation engine doesn't use a reverse rotation distributor. I have since found out that these marine SBC engines were produced in standard as well as reverse rotation with timing chain and timing gear versions of both.
I did however get the dead starboard engine running again using the standard rotation DUI distributor that was intended for the port standard rotation engine. The reverse rotation DUI distributor has been sent back to Performance Distributors to get converted to a standard rotation and I hope to be installing that on the port engine in the near future.
At this point I've only set the DUI distributor timing by ear, as both of the (2) digital variable advance timing lights that I have are telling me that the timing at idle was 39° advanced, with the engine starting and running normally. Performance Distributors advised me that a digital timing light won't work with the DUI distributor, something about their extended dwell period throws them off.
I recently located an old school non-digital timing light and printed out some timing tapes to attach to the harmonic balancer so I could check the full advance. The old school timing light is also telling me 39° advance at idle, it should be around 8° BTDC.
I'm absolutely sure that I'm clamping the timing light onto the #1 plug wire, been checked multiple times. And as I've said, the engine starts and runs great.
The only other thing I can think of is that the outer ring on the harmonic balancer has slipped, anyone have any experience with this happening?
Hopefully I'll gain some additional facts when I install the DUI distributor on the other engine and see what the timing lights tell me there.
Are there any other oddities that are associated with timing a reverse rotation engine?
My next step is to pull the #1 plug and do the finger over to hole thing to find the compression stroke and then stick something in there while turning it over with the crank bolt to find TDC, then see where the mark on the harmonic balancer is located.
