Announcing the Merc 888

**Aeroliner** · 11-29-2015

Hi Tim,
I have been looking at my Electromotive ignition system we developed and run on our 4 cylinder Mercs and I believe you can use the box with the dual output coils. It should be very easy to setup in that 2 cylinders will fire at the same time. If you need info let me know and I will E mail the Tec Manual to you. Doug has done a number of them.

Alan

**Tim Kurcz** · 11-29-2015

Originally Posted by Aeroliner

Hi Tim,
I have been looking at my Electromotive ignition system we developed and run on our 4 cylinder Mercs and I believe you can use the box with the dual output coils. It should be very easy to setup in that 2 cylinders will fire at the same time. If you need info let me know and I will E mail the Tec Manual to you. Doug has done a number of them.

Alan

Thanks for the input everybody. The 888 project has captured the imaginations of many, with great suggestions to overcome specific problems, and a fantastic array of Mercury prototype images. Please keep them coming.

This week the master & link rod concept will be developed further in hopes of using factory needle bearings and centerline loading for the slave piston. You're questions/recommendations will be answered in turn.

Tim

**Krazy Karl** · 11-30-2015

I think the master/link rod arrangement would be the best way to go. I worked on radial aircraft engines when I retired. I worked in a shop that overhauled/restored all makes of radial engines. A very practical solution to compact multi cylinder engine. The biggest negative factor is a very large frontal area, not at all aerodynamic. Not a factor here. Very durable but may not be suitable for high horsepower/rpm applications.

We had one come in that had a piston seize which caused the rod to break taking out the two adjacent cylinders. The owner was able to fly it several miles back to the airport. He had a hard time seeing through the oil on the windshield.
kk

**Tim Kurcz** · 11-30-2015

Originally Posted by Krazy Karl

I think the master/link rod arrangement would be the best way to go. I worked on radial aircraft engines when I retired. I worked in a shop that overhauled/restored all makes of radial engines. A very practical solution to compact multi cylinder engine. The biggest negative factor is a very large frontal area, not at all aerodynamic. Not a factor here. Very durable but may not be suitable for high horsepower/rpm applications.

We had one come in that had a piston seize which caused the rod to break taking out the two adjacent cylinders. The owner was able to fly it several miles back to the airport. He had a hard time seeing through the oil on the windshield.
kk

Thanks Karl,

The radial engine master/link concept is truly an elegant solution, and my personal favorite (as a fellow pilot). However, to fit the link between .535" counterweights on a .450" thick rod means the link "blade" will be only .120" thick. This translates to 64,500 psi loading in a .500" diameter pin (if it will fit the package space) using 40% surface contact. Of course, counterweights might be removed to allow use of a wider/larger diameter pivot, but at the expense of crankshaft balance.

By comparison, individual .250" thick rods transfer only 17,000 psi to the crank journal at 40% contact. The downside here is lack of roller bearings, offset loading on the rod, and small cap retention fasteners. Clearly, there's more development to go.......

Decisions, decisions.

**Krazy Karl** · 11-30-2015

I know this part was going to be a major problem using a master/link rod design. It seems all options have some kind of weak point. Certainly an interesting project to say the least. I will be following this project as it progresses. Gives me something to think about during brain idle times.
kk

**Fastjeff57** · 11-30-2015

This is totally irrelevant (but some might find it interesting): Years ago I was working on converting RR loco diesels to run on liquefied natural gas. We did 4 locos: two EMD two strokes, and two GE four strokes. The way the gas was injected into the four strokes eventually caused 7 of its 16 cylinders to self destruct: 6 on one side and one on the other bank. It puzzled the HELL out of us why it happened like that until someone mentioned the obvious: The motor used a master and slave rod system. I forget which side lost the 6 cylinders, but I'll bet it was the slave rod side that had slightly different action at TDC.

Jeff

**Tim Kurcz** · 12-01-2015

Originally Posted by Aeroliner

Hi Tim,
I have been looking at my Electromotive ignition system we developed and run on our 4 cylinder Mercs and I believe you can use the box with the dual output coils. It should be very easy to setup in that 2 cylinders will fire at the same time. If you need info let me know and I will E mail the Tec Manual to you. Doug has done a number of them.

Alan

Apologies to all as memory suggested that the ignition concept
was published, but a review of posts found it was not! See the sketch below:888 Ignition.doc

BRF didn't like the ignition upload, so here it is explained: The Mercury firing order is 1-3-4-2. The 888 is comprised of two banks of MK58A cylinder blocks; situated fore and aft. The front bank cylinders are 1-2-3-4, the rear bank cylinders are 5-6-7-8. With all eight cylinders tied to the same four pin crank, cylinders fire in pairs as follows: 1 & 6, then 3 & 8, then 2 & 5, then 4 & 7.

Does this make more sense now?

Tim

**John Schubert T*A*R*T** · 12-01-2015

Hi Tim,

Using the MK58/Merc 500 crank, did you fabricate new rods; did you just grind the originals to fit within the journal & then re-harden them;what do you plan to put between the crank pin area of the rods, some sort of thrust bearing? These questions probably are secret at this time but I'm very curious

**Tim Kurcz** · 12-01-2015

Originally Posted by John Schubert T*A*R*T

Hi Tim,

Using the MK58/Merc 500 crank, did you fabricate new rods; did you just grind the originals to fit within the journal & then re-harden them;what do you plan to put between the crank pin area of the rods, some sort of thrust bearing? These questions probably are secret at this time but I'm very curious

Hi John,

No secrets - I need all the help I can get with this one. The rods will most likely be machined from centrifugally cast 954 aluminum bronze (about 85,000 PSI), riding directly on the crank journal with lotsa oil. IF 4140 steel is selected (about 95,000 PSI), it will be bronze plated for lubrication, again with lotsa oil. My concern is that when the bronze wears through, it's steel on steel. Bronze is my choice because it's very close to steel in tensile and can't wear through.

Rod images shown on prior posts shows a 4-screw aluminum prototype with an .884" bore (.002" clearance to the crank .882" journal). It took three tries to develop a shape that would swing without hitting structure. In fact, cap end screws have to be placed inboard for swing clearance. Rod end screws are only .090" away to maintain the same 2.000" Mercury rod width. Though hard to see, screw heads overlap.

The limiting factor of these "knife blade" rods is the .250" section which limits screw size to #8-32. In fact, the standard #8-32 head is .270" diameter and must be ground to .240" to allow a little clearance!

Tim

**89HST** · 12-01-2015

Why not send the crank out to dave eden, have him machine the crank pin area wider and re heat treat it? That would allow you a little more area for bearing surfaces on the dual rod idea.