Hi all. Discovered my dearest has badly worn valve guides (apparently a known issue with early SS donks), worn exhaust valves and leaky vertical cylinder base gasket. It has just a tad over 29000 miles on it. So I'm thinking I could just fix what's wrong and then do the rest in a while, or, my personal preference is to do a top to bottom rebuild so I don't have to do it again. The bike has split 41 FCRs, modified crucifix and aftermarket aluminium cans, I've fitted 3ohm Dyna coils but I think the internals are stock. I was thinking about a 944 kit, maybe some cams, but due to the shite quality of the petrol here in NZ, I do not really want to raise compression above stock (manual states 9.2:1). I'm not looking for huge horsepower or anything silly. It actually goes hard already but a little bit more never goes astray, just not at the expense of reliability. Is there a well proven, reliable setup folks know about? It's my street bike, doesn't get raced, but does get thrashed :smile: Keen to hear your experience/opinions. Thanks.
What's the highest Octane you have? I'm sure you thought of using booster but without being able to raise compression an easy performance hike is out the window. Gas flowing valve seats, ports and combustion chambers or increasing engine capacity is probably the route. SPIKE on here hopefully will comment.
Hi I have the same model since new, done 90k miles, went 944 cosworth pistons @ 35k, total rebuild imminent, was thinking of new J&E pistons (£250 pair) if bores are still ok. Mine was thrashed for years as a 944, no reliability issues with big bore, go for it Original valve guides were shite, mine were shagged @ 15k miles keep us posted on your rebuild chris
Highest octane readily available is 95 RON (which would be lucky to be 83 MON). The bike goes well on it, even though it's nearly 50% Toluene (enamel paint thinners). We have BP 98 RON, but not available everywhere. I use that in my 160cc two stroke lawn mower because walking around behind it on 95 gives me a headache. I could go up a little in compression, but I think from memory, 9.5:1 is nearing the safe limit for a carburetted engine on this fuel. Also these early 900's were a bit over-geared on their starter motor so raising compression too much can cause other issues. I've got two months left of tax to use up then it's off the road. By then it will be well tired.
Thanks for the intro Chris. Two or three ways of looking at this, valve guides are a pain, and still they make em like it, easy fix for a machine shop or someone who can hod a screwdriver. guides available from the states as aftermarket or ducati. The 944 kit is more involved as the pistons need to be the same weight as std if you are going to rev this (everyone says they wont, they lie!) this needs a crank balance if the pistons are differing weights. I would figure to have the crank out anyway at that sort of miles as the crank will be waiting to go bang anyway, it will be full of sludge in the oil gallery (trust me). The compression is an easy fix if you use JE pistons, i just machine the tops down to the required comp ratio, i have reliably taken 4.5mm off the crown to do this but in your case go more like 3mm. Another fix is to stick with high comp and buy an ignitech ignition, if you dial less advance in this should fix the knock. Let us know how you get on.
So what is the advantage of 944cc over standard? Much horsepower/torque increase at all? The JE Piston kits are a good price, there's a fellow in town that is an experienced crank balancing guru (I'll do that anyway), and a company less than 200 miles away does silicon carbide cylinder plating so that's all good. Plus a Ducati shop in Nelson do gas flowing/head rebuilding etc.
I can only give you a seat of the pants figure, but felt like a grunt monster in comparison to standard, I have to say never reved mine over 8 once I had the big bore, no need, shortshift for the grunt...
Spike, when you say 3mm off the top of the JE piston, would you happen to know roughly what compression ratio that would give? The bike had a broken oil ring on the horizontal cylinder so it's 944cc time.
RIXSS, to nail the compression down to an exact figure you will have to measure everything and do a dummy build, this is not difficult but very time consuming, well worth it in my opinion if you want to make good power. Another consideration to think of when choosing your given ratio is the spec of motor you want to end up at. again my choice but I feel as the port is improved to flow more you need less comp ratio, this "improvement" could be a flow job or a pair of cams, or of course both if you are really going for it. My quote for 3mm from the top of the piston was for a middle of the road build and i would be aiming for 10:1 to 10.5 :1 if i had no means of adjusting the ignition timing. Be very aware that the JE piston comp ratio seems to be always higher than stated on the box and whilst fine for a motor that is otherwise stock as soon as any improvements to flow are made the comp ratio may be too high and give a knock at low rpm. Remember comp ratio can be altered if you have had any valve work done, ie seats cut, new seats or bigger valves. Another problem with high comp ratios is starting, great, build a killer motor at 13:1 comp then find the starter wont turn it over, even with a sidecar full of batteries. Measure twice., build once. (or in my case about a dozen times).
Interesting thread, and good timing. My '95 has around 24k mile on it. I'll have the engine out shortly and am toying with maybe giving it a bit of a birthday I'd like to get plenty of mid range grunt, I'm not looking for a high revving motor. JE High comp pistons along with a balance and a bit of love to the ports has been mentioned as the most effective way ahead. This is without going to Ignitech, flat-sides, full Spaghetti systems etc. What's the latest wisdom of how to liberate more torques on the 904 motor?
IMO best way for most torque on a low revving two valve is by going big bore with a set of the original Ducati performance cams, stump pulling under 7k.
Well I stripped it down. Not.Very.Pretty. Eight cogs in the 'box knackered. Broken oil ring on the horizontal cylinder. Crank shaft had just started to spin in main lhs bearing. Fortunately wear is less than half a thou, so loctite will be fine. Bores were on the limit, $980nzd later and they are like new to match the 94mm JE piston kit. Currently awaiting big end shells, primary side main bearing, studs and a tacho cable. Oh, and the gearbox... I'm hoping for those bits before the holidays so I can work on reassembly.
I have a few gearboxes, yes post will be a pain but if you are struggling give me a PM. Oh, just to be clear, Windmills and clocks have cogs, bikes have gears.
