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Discussion Starter #1
Hello all,

I should start by saying that I am new to this forum and working on Ducati's. I have owned and worked on about a dozen bikes, but a majority have been old Honda's and I don't have a lot of experience with engine work. The most I've done is a top-end rebuild on a Honda Trail 90.

What I have now is a 2000 Monster 750 with 20k+ miles and a very spotty history. From what I know, the previous owner had the engine apart and replaced the bearings with bearings from Napa (n). Then it bent a valve in the rear cylinder that was fixed at a sketchy shop in Aloha, Oregon which is now out of business. It never ran right after that and the only detail I have is that it would backfire a lot. It was then taken to Ducati where they said the crank knocked and it sat ever since. I now own the bike and what I know for sure is that the rear cylinder's compression is at 95 psi and 120 psi with a little oil poured in. I have the engine out of the bike now and had a look in the cylinder where it's got a pretty nasty gouge on the cylinder wall and an interesting impression on the piston.

Before I dive into the bottom end to figure out what the deal is with that, I'm just curious what my options might be for fixing this rear cylinder. I found a used jug and piston on eBay for $200, maybe I could pick that up and get both cylinders honed? I'd like to do this as cheaply as possible so I don't think boring it out is an option. I'd also like to try and fix this engine rather than buying a used one so I can gain some experience, but I'm a little clueless at the moment. What might some of you with more experience do in this situation? Any input is greatly appreciated, thank you.

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Can you tell how deep the scoring is? It may be a little too deep for just a hone. It might need to be bored oversized. Not sure if they sell oversized pistons but if they do, that may be the way to go for that one cylinder.
 

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Used cylinders and pistons would probably be your best bet right now. Nikasil can't be truly honed. The cylinders can be bored a small amount and replated. An experience that will run about $500 and only a handful of places across the country do it. Then you'd be faced with having to find matching pistons. So yeah, keep your eyes on eBay.
 

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Discussion Starter #4
If I got just a cylinder and piston, the cylinder would have to be machined to match my cylinder head right?
 

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well, that cylinder is toast, Someone has tried fixing the scoring and has done a dodgy job, also looks like it's been honed roughly. Dent in piston also, it's gone. :cry: ..Not good.
As Dvy3178 has said; boring oversize is only possible if you can find a place that does Nikasil plating, AND, has experience with cylinder liners. There are no steel liners in later Ducati's, unlike old Honda's or such. Ducati do not sell oversize pistons as such.
I do remember someone making oversize racing pistons, out to 785, but again re-plating is a must. Very expensive.
as an example.

Second hand barrel and piston is the way to go. But, I would hold off on that decision until you get bottom end apart.

Now, the dent in piston, any damage to big end shells is the next question, you did say knocking, yes.
check the bearings and rods.
Bent or dropped valve? check valve guides for gouges or cracking. Sadly it goes on.
sometimes cheaper to buy complete second hand engine, if any bottom end issues as well.
 

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695 motors are always on ebay for very little money. I wouldn't want to downsize to a 620, and 750 stuff is getting harder to find. I don't know if you're running carbs or injection, but either way you could probably make it work.
 

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Discussion Starter #8
It bent a valve and that appears to be properly fixed, but they obviously didn't know what they were doing so I'll have to look further into it. The compression test I did on that cylinder was 120 psi after I poured some oil in the cylinder so I'm assuming the valves are probably fine. Going with a used cylinder is definitely going to be my best bet after I have a look at the bottom end.
 

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What the f.... am I looking at here ? A piston broken in half ?
 

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Haden, The Nikasil is very thin and is undoubtably damaged and I agree that you best bet is to find a used replacement. The damage is at the very top of the cylinder , which is a good thing as far as saving the cylinder is concerned. As a Certified Redneck Engineer, I would clean up the cylinder and run a stone type hone through it From the Top of the cylinder 2 or 3 strokes, top to bottom, then place the hone so the pivot on the stones is just inside the cylinder and do a couple more spins, just to thoroughly clean up that top 1/2” of the cylinder bore. Then wipe it clean and see what you have. It “ might “ be salvagable if you want to try to fix it on a tight budget, but that depends on the condition after honing it. Don’t overdo the hone, the nikasil is very hard , but very thin. Once you do this, you’ve done as much as you can do with what you have. If it cleans up, and you can find a piston and rings, it could run ok. The damage I see is so close to the top of the cylinder it could be usable IF you can’t find a used cylinder and piston on eBay. I broke a ring and found a new piston and rings for $100. Last time I checked, I think rings alone were $95 a set from Ducati, and it looks like you’ll need a piston and rings , regardless. I have a habit of cleaning things like this up just to see a “ best case scenario “ of the damage. I used to race 2 strokes , and cleaning up minor damage for the next week was a regular occurance.
 

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Hi Duc,
I believe the picture is a very oversized high performance piston, sitting on a barrel that is way smaller.
We have similar credentials, down here we're called 'Bush mechanics' :cool:

Also, Run a stone hone through a Nikasil plated cylinder and it would be trashed, as you said the plating is very thin, we're talking micro thin, A rough stone would destroy the plating. It looks like someone already has.
Yes, they can be 'deglazed', but with very, very, fine emery paper or cloth, 1500-2000 maybe, just to remove surface glaze when new rings fitted.
Even if it cleaned up with any honing etc. it would not last very long at all. The rings would eventually tear into the soft aluminum bores and make a mess. I wouldn't take it on any inter galactic journeys. ;)
 

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Incorrect, fellow bush mechanic . You can run a hone through a Nikasil cylinder and it will barely scratch it. That stuff is hard as diamonds ! I’ve done it, as I said, no pressure on the spring adjustment , 3 stone type hone, not a “ball” hone, be careful, only a couple of passes. Or no hone available, just try smoothing that damaged area with Emory cloth for a better look. Can’t blame you for being cautious, but in this case the cylinder is trashed if it can’t be repaired, and it’s going to be cheaper to find a used one. If the damage is above the top ring, which it looks like it may be, no sealing ability will be lost. I would only mention it because I’ve done similar in the past, and it will only give a better look to make a decision in case a good used cylinder can’t be found. I don’t know this quotes origin, it was hanging in the local bike shop:
” I have done so much with so little for so long, I am now qualified to do almost anything with practically nothing.”
 

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Haden, The Nikasil is very thin and is undoubtably damaged and I agree that you best bet is to find a used replacement. The damage is at the very top of the cylinder , which is a good thing as far as saving the cylinder is concerned. As a Certified Redneck Engineer, I would clean up the cylinder and run a stone type hone through it From the Top of the cylinder 2 or 3 strokes, top to bottom, then place the hone so the pivot on the stones is just inside the cylinder and do a couple more spins, just to thoroughly clean up that top 1/2” of the cylinder bore. Then wipe it clean and see what you have. It “ might “ be salvagable if you want to try to fix it on a tight budget, but that depends on the condition after honing it. Don’t overdo the hone, the nikasil is very hard , but very thin. Once you do this, you’ve done as much as you can do with what you have. If it cleans up, and you can find a piston and rings, it could run ok. The damage I see is so close to the top of the cylinder it could be usable IF you can’t find a used cylinder and piston on eBay. I broke a ring and found a new piston and rings for $100. Last time I checked, I think rings alone were $95 a set from Ducati, and it looks like you’ll need a piston and rings , regardless. I have a habit of cleaning things like this up just to see a “ best case scenario “ of the damage. I used to race 2 strokes , and cleaning up minor damage for the next week was a regular occurance.
Please take me to this Ducati dealership that sells ring set for $95.
 

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How much are they now ? That was the price I was quoted 3-4 years ago. I checked into buying aftermarket WiseCo pistons which use their own brand of rings which are much cheaper, but I found a brand new piston with ring set on eBay for $100.
 

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Well, I guess $95 wasn't too far away for a single set. The 88mm for the 800/695 motors are at $135 right now. Perhaps in my mind I was thinking of the total cost for a complete set. Still, that's getting close to $300 just on rings to freshen up the top end. I'd gladly add a couple hundred to that for quality aftermarket pistons if it meant more reasonably priced rings down the road. I just haven't been able to track down whether or not there's a difference in the compression height of the 800 pistons vs the 695. I highly doubt it, but I'd like to know for sure.
 

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That was my thought too, before I found the piston w/ rings on eBay. I went the cheapest route.
 

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Back to the subject. The cylinder scoring and the dent in the piston dome point to something in the combustion chamber that shouldn’t have been , during operation. IF you wish too see how bad it really is and if there is any chance of cleaning it up and using it , I have outlined the procedure, which I have personally used in the past. The better alternative is to procure a usable cylinder/ piston/ rings, but I don’t know your budget. I always like to clean things up and see if I may have options.
 

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Haven't heard from 750 guy in a while. I wonder where he's located? I'm talking to a guy right now with a clean for it's age 1999 M750 with a clean title apparently. $640
 
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