?s about Merc I3 and I4 looper motors

[twright55]

I have a few questions about these motors. I have an off-shore '96 115hp w/ a locked up powerhead (one rod, bore and crank are trashed, I think), and I've been looking for a 90hp powerhead to replace it with because it's lighter and more in the power range I am looking for...I have a 14ft boat and want to keep the draft as shallow as possible, while still producing some speed) I found a nice, clean,...and cheap...'87 70hp model (i3 looper) for sale locally (nada says 265lbs vs 350lbs for my 115)...but I really want at least 90hp. thus the following questions:

1. for the I3 motors (from about '87 up), what is the difference between the 70, 80 and 90hp versions? Is it only the carbs, or reeds and carbs? It seems that the blocks and pistons have the same parts #s, so I'm guessing the ports and compression are the same. So could I use the reads and carbs from my 115 to make more power (yes, I know two of the carbs on the 115 have no idle circuit...but just ignore that for now ;) )

2. Can an I3 power head be put on an I4 mid section? The only reason I ask is because my 115 off-shore mid is pretty nice, and I'd keep it for a back up if it is compatible with the I3 powerheads.

3. What is really different about the offshore models, anyway? According to nada, the offshore models weight 20lbs less than the regular models...is it because they use a lighter alloy? That'd be another reason for me to keep my offshore mid and lower for use with (or backup for) this 70hp if I buy it.

Thanks for ANY help or advise. I am a technically minded person, but I really don't know a lot about outboard motors.

[ChrisCarsonMarine]

There are two series of these motors,the first few years 3+4 cyl motora were 3.375 bore,i think,and bottom guided on the crank.The 70 you speak of is in this catagory.Later,around 99 or so[no book nearby] the 3+4'swint to 3.5 bore,and top guided.So,the bore is different old to new versions,also,the stroke is different between the two.In the same engine group the HP is changed by carbs,the reeds are the same for all,early and late.I think the bolts or studs[both wave been used]are larber dia. on the later series of motors.I believe the 70 p/h will mount to your 115 mid,if you use the 70 bolts.The old 70 is not as powerful as the newer big bore one.The gear ratios are different,the 4 cyl lower spins the prop faster than the 3.You could find small bore 90 carbs and use the 70 p/h,but you'll be taking a big hp loss.Hope this helps,Chris

[twright55]

Ok, thanks. That is exactly the type of info I was looking for.
I am aware of the small/big bores (big bore started in '94, btw), and the differences in gear ratios.
I was NOT aware of the differnce in studs...which is good info.

This 70hp is cheap enough that I may just buy it to get out on the water, and graduate to something bigger/better later on.
I'm just trying to figure out what parts (if any) are worth holding onto from the 115 offshore (if they are really all that rare/superior) to use on an i3, or rather I should just ebay them. and save up for a 'real' motor ;)
I was really looking for a yamaha 90, but people seem to think their worn out used one is worth 2oz of gold, when v4 crossflows and mercs can be had for 1/4 the price all day long.

[ChrisCarsonMarine]

How abour rebuilding the l4? I'll rebuild yours with warrantee for 24-2800$,price depending on condition of block,free pickup/delivery,upgrages available,Chris

[twright55]

I'm planning on posting some pics of the motor (I've already torn it down) to determine if it is even rebuildable.
I am afraid the crank may be toast. The block should be good with the replacement of one sleeve. The piston is siezed up in there real good, and it looks like a mess. The rod bearing seized up and the rollers were worn down flat at the crank...can only imagine what that did to the crank.
I bought the motor already seized for less than what I know I can sell the lower for...I was hoping for an easy fix, but after tearing it down...I don't think so. I honestly think it's a parts motor now.

Does an offshore, big bore block in need of one sleeve have any value beyond scrap? If it is really a lighter, more corrosion resistant alloy, I would think so...unless replacing the one sleeve is to expensive.

[ChrisCarsonMarine]

I don't think there's anything special about the weight or alloy of the block,I don't think there is much value in it,even if it can be re=sleeved,which is unknown at this time.That is why I quoted 24-28$,I'm sure the crank is bad if the needels failed on it,Chris