Old 1972 100hp Starflite advice (rebuild)

[ILLaViTaR]

Hi all I posted on here a couple years back regarding an old 100hp evinrude. With everyones help I managed to get it running and then it blew a crankcase seal. Here's a video of it running just before I stripped it down (evinrude 100hp - YouTube). I ended up taking the whole motor apart to replace the seal and never got around to putting it back together it's been sat on the bench the whole time. I've bought every gasket and replacement part I need put it back together and get it running right now but I want to do make sure it's all done correctly and lasts the long term. The main issue is I've spent too much on the motor already and don't really want to spend anymore if necessary.

I noticed when I stripped it down one of the low idle jets in one of the carbs has been burred/chewed out by a screwdriver which would probably explain why it cut out in that video. One of the spark plug sockets in the head is stripped also but mainly when taking it apart every single bolt was corroded I lost most of them they're not reuseable so I'll need to source new bolts somehow to the correct specs, some snapped threads are still stuck in the block and there's black tar/carbon absolutely everywhere inside exhaust of the motor that nothing seems to clean off.

Currently the powerhead is on the bench (crank/pistons are not removed) and I was hoping to just clean everything, fix the idle jet/bolt problems, reseal the crankcase and put it back together. But a couple people on the video commented saying it's overheating or the rings are stuffed.. which means more money I don't really have but it's something I need to address now while the motor's apart and the powerhead is out on the bench, if it is stuffed/overheated does that mean I'd need new pistons and rings? Then the bores honed by a workshop? And then the block sandblasted and acid washed etc? I'd love to do all that but it would be ridiculously expensive I'd imagine I'm hoping to avoid taking the crank/pistons out or anything to do with a full rebuild I only took it apart to replace the crank seal originally.

I'm just worried I get it all back together running and it breaks again! The smart thing to do would be to obviously rebuild it while it's out but is it really necessary? I did a compression test and all 4 cylinders were good it's just the knocking noises at idle that concern me. I'm not sure what to do I'm really hoping to avoid any major expenses/rebuilds if I can though!

cheers

 

[racerone]

Re: Old 1972 100hp Starflite advice (rebuild)

Remove the bypass covers to look at the pistons and rings.---2 covers on each side of the block held on by 6 small bolts.

 

[F_R]

Re: Old 1972 100hp Starflite advice (rebuild)

I would add the exhaust cover to that (the one between the V). You will be able to see the exhaust side of the pistons, which are likely to be scored if it was overheated. Besides, if it has been overheated, those exhaust cover gaskets must be replaced anyway. If they leak, water squirts into the ports and destroys the whole thing.

I don't know exactly what knocking noises you are concerned about, but let me say that is not a quiet engine like a car. It has roller bearings and a ton of slop at the head end of the pistons (they are tapered). All that stuff is noisy, compared to a car..

 

[emdsapmgr]

Re: Old 1972 100hp Starflite advice (rebuild)

When watching the video, I did not see a lot of water streaming from the lower unit...while running. Was it overheating during that video/test? Does the hot horn work? Now that the heads, intake side covers and exhaust manifolds are off, you can move the pistons inside the cyls. enough to see if the rings in each cylinder are intact or not. If the head face has pits in it-likely the top ring is gone and you'll need to pull it the rest of the way down anyway. Those engines do knock when they get high hours on them. My 79 85 hp was a high-hours knocker. Actually, it's piston slap. Once the pistons wear into the cylinders, the clearance opens up and they slap back and forth as the engine strokes. Once these engines loosen up, it sounds bad, usually at idle-then gets lost in the noise of the engine at WOT. The slap is not necessarily an indication of imminent failure. Probably will go another 5 years.... I wound up boring my 79 .030 over and installed new pistons and 79 is now quiet as factory new. From your comments, yours must be a high hours engine. You might just want to pull it apart completely. See how the cyl liners look. You really should install new rings. No point in reassembling it and then having an original/old ring break, damaging the head face and piston. Since it's a knocker, probably should be bored with new pistons/rings. Not unusual to see jets with damaged screwdriver slots. (the factory uses a special screwdriver- part number: 317002) Just because the slot is damaged does not mean it won't flow fuel properly.. visually check the jet opening.

 

[racerone]

Re: Old 1972 100hp Starflite advice (rebuild)

You really need to think this over / do some looking.----That motor has an expensive hard to diagnose electronic ignition system.------It has electric shift.-Electric shift is very good if it is in good working order only.---Myself I would look for something in the early 1980's OMC V-4 and rebuild that.---Lots of those around too.