Merc ignition stuff 4's & 6's

[RogerH]

Hello John,
I started messing around with these ignitions about a year ago, and partnered with Larry McAfee to evaluate them. Larry's son Kevin is actively racing C,D&E Mod in NBRA and did very well running these ignitions last year.
The distributor is universally used across the Merc650 (4-cyl) to Merc850 through the late 70's. They are battery operated but triggered by the distributor. The large coil you spoke about was used on the 650's+ but the 85hp version came out with the smaller coil you see on the Looper. The coils (both) are bullet proof and generally never fail.
Larry built a tester that drives the distributor with a air driven die grinder (in excess of 11,000rpm) and a pressurized chamber with a plexiglass top that houses the spark plugs. With a simple wiring harness and battery the whole system can be bench tested at RPM and under simulated cylinder pressure. The cylinder pressure is critical, as it effects the spark in a big way. We can see no difference in the large vs small coils. Thus the small coil is able to charge/discharge (saturate) as well as the larger version. The switch box and coil can be mounted in the boat or on the motor - your choice. The switch box does draw in excess of 5 amps (less than 7) at higher RPM, so don't skimp on the wire size.
The CDI/Rapair replacement unit is a bit more efficient (uses less power) than the Merc unit. It requires the use of their coil with their switch box. They also make a replacement trigger which is housed in the base of the distributor. Their trigger uses magnetic switching vs the optical switching of the Merc unit. Magnetic is preferred over optical. Thus they provide a steel disc for the trigger. BTW, there is an up/down orientation on the disc that must be followed for correct timing. They are usually labeled.
That's a crash course in the Type IV ignitions. Good question, hope this helps to answer your question. I should warn you that some of the switchboxes have a rev limiter installed. I usually buy the 6cyl version to avoid that - Roger

[John (Taylor) Gabrowski]

Roger: Thanks very much for the session. I have only one distributor like yours and I got a load of those smaller coils and the system as well as the earlier systems all used that big hockey puck coil. That same system was on pics from a Merc D Mod Fast Fred sold a while back too and its a nice compact setup that is a for sure.

I suppose that using the small coil on a Merc Lightning Energizer/Distributor for Merc 4 cylinder engines would then also work too? Nicer things with some experiments can sure come in small packages. :)

Not long ago (couple years back?) to cut power consumption down on the Merc CDI systems with the hockey puck coil, I went on a weekend binge at an auto wreckyard to look for low drain high output solid state system ignition coils and found one Honda coil that belted out 30KV at 12 volts unpressured and could go up to 60KV when the system called for it. Nice thing was that you can use 2 -7.5 volt RC stick batteries to power the Merc trigger box, the Honda coil and the needs of the magnetic or the LED distributors for half and hour and then use the quick charger attached to your car battery charging system to regain it all in less that 15 minutes per battery stick. That takes out the 12 volt heavy marine utlility battery out of the boat and gor those that liked to use 18 volts out of 2 marine lead accident batteries, the 15 volts out of the 2 RC battery sticks does the trick with the Honda coils. Seeing you guys are now using that small Merc coil not a bad thing to see how long 2 RC batteries would last with that coil plugged in.

I heard that there were rev limiters on some of the 4 cylinder trigger boxes, any way of telling those apart from those that don't have the limiters other than going to a 6 cylinder box?

That is all one nice compact system! :)

[Mark75H]

Roger, I've had enough trouble with 6 cylinder boxes that fire but get weak after about half a lap. I've given up on them and use all CDI boxes. They fire my 6's off easier and let me use less choke. Like you said, they use a lot less power. I think it is 1 amp vs 6 amps.

[RogerH]

Concerning the Sw.boxes, I really don't know how to tell which ones have the limiter. I think it is safe to assume the boxes marked 6-cyl do not (at least when used on a 4-cyl.) and these were used on the 454 I/O's too - all the same part number. I agree with Sam that the CDI is an overall better unit and its packaging is better (Sw.Box & coil on same plate). Their power output is better, that's the key. Pretty good price and I think they give APBA members a discount.
Question to Sam: Are you using CDI's trigger or a Merc trigger in the distributor? The job of the Sw. box is to fully charge the coil before it needs to discharge to fire a cylinder. If the RPM's get too high the coil may not get fully charged and the spark falls off. Also, if the optical trigger fades (with age or grime) it will actually change the dwell time as it triggers the switchbox late. I don't think that is why you're seeing certain Merc boxes fade away. Don't know why.
I wouldn't mix and match coils with switchboxes. The switchbox and coil are engineered to work together. CDI has the advantage of a newer electrical design and better magnetics for use in the coil. The CD units fire hot a 0 RPM and thus help starting a lot. I personally like the Oddesy batteries as they pack a punch given their weight / size and hold a charge while not in use. Worth the money!!!
BTW these are a Type III not IV system, my mistake.

[Mark75H]

Roger a 6 cylinder switch box will not work correctly on a V-8 ... it will have the wrong tach signal

I haven't had any trigger failures other than bad insulation on wires so I'm still using Merc triggers

It is rumored that some of the 6 switch boxes were limited, but some people who should know say none were limited

The big difference in the original Merc switch boxes is the tach output signal

I agree, I would not take the little OMC coil off of a CDI box either ... it works fine. The Merc coil that works with the Thunderbolt distributor is actually a medium sized one. The small 50 hp ADI coils will not work with the Thunderbolt distributor for more than a few minutes before they burn up. The slightly larger Merc coil and the tiny OMC coils will work

I like the Oddesy batteries too. About 20 - 25 starts of my padded 6's on a charge

[John (Taylor) Gabrowski]

When I quite trying to develop a dirct charged Merc & Mariner 3 cylinder 2 carb 3 Holer I just set aside their ignitions when I got rid of the blocks. I never gave their ignitions a second thought until I started looking at a second Crescent. If a 6 cylinder Merc trigger box will work on a 4 banger Merc sans the tach circuit would not the 3 cylinder trigger boxes work on a Merc 3 cylinder too sans its tach output?

[Mark75H]

yes yes

[RogerH]

I agree that the tach ckt. is different in the 4-6 boxes and the I/O box, but the I/O box will work fine (sans Tach). Basically, that's why Larry and I run all of our Sw.Boxes at speed to verify they aren't limited. I haven't found anyone who knows how to tell unless you knew what year motor it came off.

Careful on the 3-cyl boxes. Remember that the switch box is triggered by either the distributor or flywheel magnets/coils. I think that all of the 3-cyl were flywheel triggered - not sure. In this case (Type IV I think) the switch box generates its own power from the stator and is triggered by another set of magnets / trigger coils under the flywheel. The 6's just use two of these Sw.Boxes (and a different F'wheel trigger.
I haven't had the best of luck with my 6-cyl. motors (stock) and this ignition. The Sw. boxes are EXPENSIVE and I was told that you shouldn't mix different revision code boxes on the same motor (2X expensive!!!) I always thought their low speed spark was weak. Does anyone have a good replacement - setup - suggestion for the 6's???

Maybe we ought to move this to a technical thread?

[Mark75H]

If you are going to speed test them, I'd recommend you do a 10 minute minimum run at speed

I've never heard anything about a mismatching problem with switching switch boxes on distributors and have had no problems that seem to relate to a mis-application. I don't know if that makes me brave or stupid. CDI only makes one replacement box for all the 4 & 6 boxes.

When the Merc boxes were new their low speed spark was impressive ... maybe SCARY is a better word. If you've had some with weak spark at any speed there was something wrong with them.

I use Merc triggers and CDI boxes on my 6's (all padded, one has 275psi cranking compression). They fire instantly and need little choking even on the chilliest days. This was not the case with old Merc boxes. I would not even trust a NOS Merc box ... they haven't been made in many years and could go bad just sitting on the shelf in my opinion.

I have a bunch of used Merc boxes that I would be happy to get $30 each for if anyone wants them.

[RogerH]

Sam, I messed up, as I was referring to my V6 motors with flywheel triggered boxes in my last response. I am most impressed with the low RPM spark on the Type III boxes, but haven't experienced that on the V6 boxes on my XR2 and XR6 motors (Type V boxes). When I needed to replace one of the boxes the Merc dealer said I shouldn't mix different Rev. code boxes. Not sure why he said that, but suspect he was trying to get me to buy two boxes!

[RogerH]

The first photo shows the basic parts of this ignition. I didn't have the smaller coil from the 850 in this picture. The switch box is P/N 332-2986. The small 850 coil is P/N 332-4895. You can buy the screw-in terminal ends from NAPA or Sierra. I buy Accel 3000 series solid core 7mm Si wire sets that come with 90 degree spark plug ends. These are readily available from Summit Racing for around $23 (for 8). The summit P/N's are ACC-3009 for yellow and ACC-3009B for blue.

The 2nd photo is the CDI/Rapair replacement unit. Note that the switchbox and coil are combined on the same mounting plate. This Sw.Box will not work with a Merc coil. It will work with a Merc distributor trigger or CDI's trigger.

The third photo is Larry McAfee's test set-up. You can see the die grinder driving the distributor and the spark plug pressurized chamber. You can observe the spark through a plexiglass cover on the chamber.

[John (Taylor) Gabrowski]

I have both flywheel Mariner 3 Holer 3 coil and belt drive Merc Distributor 3Holer ignition systems, I know you can't mix them up. I am looking at using the Merc belt driven for the second Cresscent (a Toronado 650) instead of what it has ,you can't get any parts for anyway so Merc it is.

As for MercéMariner discharge voltage and being told to be careful I learned the hard way using the Mariner, I know what being fried on the spot is all about thanks to a direct wired tach that works of sparkplug voltage when you throw its toggle switch! Never again will I ever do that! ever!

[RogerH]

This is the Type III ignition that Sam has been mentioning. It is definitely the way to go for overall performance. This distributor happens to have the CDI trigger as well. The wires were rotten going into the distributor, so there was no way to fix it. CDI supplies the complete base, bearings and new 4 & 6 cyl trigger wheel. The CDI trigger wheel must be used with their trigger as it is magnetic vs optical (Merc). The motor is a Mk58.

[John (Taylor) Gabrowski]

That is all a very nice aftermarket install that is for sure. What are the aftermarket parts cost globally for an engine.

I am still blessed with having a dozen or so complete overhauled P4D Merc mags with lots of spare parts so going that route for gassers is not in the cards but I sure do see the point for fuelers which can be difficult.

[RogerH]

This will be tricky at best. The $$$'s depends a lot upon your connections with friends, dealers, and eBay skill. eBay buying has really gotten hard on these items. Their demand has risen and I think that most of them are going to people that are trying to repair their 70's+ vintage motors.
I feel the distributors are the major item. Anything under $140 is great. Don't forget that everything counts - cap - trigger lead condition. Count on replacing the bearings, but everything else will probably be OK.
The switchbox is $30++ for a Merc. and it could be DOA. They are easy to bench test, but not many people know how to do that. The CDI box with coil is around $155 I think. I believe that is the dealer's cost.
Merc coils are pretty cheap but the small ones don't come up on eBay much. I find them in dealer's scrap heaps.
I have bought 4 whole 650's (4-cyl) for a steal just to "rob" the ignitions out of them.
Don't be in a hurry and you can scrounge this stuff rather reasonably. While it is more money, I'd shoot for the CDI switchbox/coil - but - you always need the distributor.

[John (Taylor) Gabrowski]

These days you can snag older Mercs and Mariners complete sans gearcases for $50.00 to $100 bux but the 3 Holers in them are at the point where there is a problem giving them away for anything tangible and usually they are top cylinder fried anyhow so its for ignitions or parts to keep another one running. Aeems everyone in the marine industry thinks them the worst of a joke and lemon on Mercs part. People still ask me why Merc discontinued the 4 banger 44s as that was their most successful engine to so many. Change for the sale of change? or just to make more dollars changing engines no matter what loyalty.

[Mark75H]

Roger, how much air pressure do you put on the spark plugs while testing?

My father had a spark plug tester that had a pressure set up like that when I was a kid.

[RogerH]

Usually we use 150psi This could be adjusted for padded motors, but the plexiglass cover will limit the amount. We really need one of the positions to have an adjustable air gap to distinguish the best systems.

[Mark75H]

Maybe a chamber with a long projected nose spark plug and an adjustable ground. There are some commercial boiler ignition spark plugs that have a very long insulated nose and a standard 14mm screw in base. I'll keep my eye out for one. If I remember correctly 100 psi was enough to blow out some junk. 150 and some extra gap should be a very good tester

[legend41]

I too am working on one of these ignitions and I would like to order the CDI complete kit. The question is where did you order from and is the kit number 114-2986K1? A second part is the linkage, on one of the pictures looks like you were able to adapt to the older Merc. Mag arm ( I would like to rotate the Ignition like the older Mag.) but it was not too clear where you attached the side Merc lever, how about another picture of that side of the motor? And last question is concerning the engines timing. Did you retard or keep the current timing you had?
Thanks for the help.

[RogerH]

The CDI kit P/N is 114-2986K1. It includes the 114-2986 switch box, 134-3736 trigger, 4-cyl trigger wheel, spacer and bearings. This basically replaces the base of the distributor with CDI's base/trigger. Be sure to use their trigger wheel as they use magnetic vs optical(Merc) sensing. You will have to disassemble the distributor to install all this stuff. The attached picture of the Mk58 uses their kit. I ordered it through a local dealer who sell it to me at his cost - good friend! I've heard that CDI gives APBA members a discount but haven't checked into that. Look up their sales and tech phone at cdielectronics.com. Their technical people are really helpful and good people.

The timing will change quite a bit from your magneto timing. The mag usually is set around 0.375" BTDC and the CD ignition seems best around 0.200" BTDC.

I chose to swing the mag as I use this motor for river racing. These ignitions fire excellent at low RPM so starting them at full advance is not really a problem. I see no disadvantage in swinging the distributor as I set the stop screws the way I wanted full advance and can set the throttle opening at full advance too. Idle/start can be set as well. I hope the picture helps with your linkage question. Give me a call or eMail if you have further questions. - Roger