Hi All, I'm looking to pull apart my '95 M900 this winter for a bit of a cosmetic restoration and I might take the opportunity to do some engine work. Just thinking ahead so I can make sure I have everything I need. I also have a complete ST2 engine and I know the barrels can be modded to convert them to oil cooled and used with the pistons to give 944cc, I also know that the ST2 cams are seen as a worthwhile upgrade. The complication is that the Monster came to me with high comp pistons but the standard bore. Carb-wise the bike has recently rebuild Mikunis. The bike is used for general hooning around on and the occasional blast around the country roads, it will never see a track. So my questions are: (1) Would I be better off sticking with the 904cc high comp setup or swapping in the ST2 barrels and pistons to give a standard comp 944? I don't want to spend a fortune so buying high comp 94mm pistons is not the direction, although possibly I could part fund them by selling the 92mm ones... (2a) The ST2 cams are a given, but can I go with the complete ST2 heads? I understand from my research that there are benefits to be had with bigger valves and improved gas flow. There's a lot of info out there on converting the barrels to oil cooled so I'm happy with that operation, but I can't find anything on converting the heads? (2b) Or is it the case that ST2 heads are a direct fit to oil cooled barrels with no modification necessary? (3) If the ST2 heads can be used will they work with the standard M900 barrels, so could I use them if I stick with the 92mm/904cc high comp setup? I'd welcome any views based on experience, or any pointers to other threads or resources that could help. Thanks in advance Darren
Having modified an M900 to a 944 with ST2 cams, I looked into many options. I bought an ST2 engine as a cam donor but didn't use any other components as I felt it better to bore the 900 heads out to 94mm and fit high comp pistons. Some opinions; I would think a good 904cc with high comp pistons may well out perform (or at least match) a 944cc standard comp and so would suggest that it's a lot of work for probably little or no gain? ST2 cams are more beneficial for shorter intake tracts, not sure on standard long manifold intakes? Not sure if ST2 heads would work with Monster cylinders but they don't have much finning on them so may not cool so well?, I'd stick with the 900 heads and unless your 900 is the later, small valve/head version then the valves are the same size anyway. Personally, I would (and did) go with big bore, cams, high comp, short intakes, FCR etc. and sell on what's left of the ST2 to recoup some of the cost, you won't be disappointed.
In my experience you'll get more out of replacing the standard IC Ignitors with a programmable Ignitech ignition system and a decent set of Coils. The Ignitech was the best £175 I ever spent on my M900. Nasher.
Hi Darren, I have a project underway that is based upon a 900ie. I also considered the same options. In the end I purchased Hi-comps from JE off ebay USA, even with import tax it wasn't that expensive (I think 370$ all in)..as I was purchasing the hi-comps I decided to go to 944 (pistons the same price for +2 diameter as std hi-comp diameter) and bought 2nd hand ST2 heads to convert to oil cooling. (including st2 cams)...I can't really report on the performance gains as all pieces are still being collected! If you are tearing it down though I would do the max you can, as you are already in there...I'm sure the high comp 904s would sell to cover the cost of the 944s However once you start you will also need...Nichols featherweight Flywheel, alloy adjustible cam pulleys, lightweight clutches.. head porting work..etc..etc...etc... slippery slope! Good luck! Grant
Totally agree with this..I'm not sure why everyone doesn't fit the Ignitech especially as the Kokusan boxes are £100 each second hand!!
Thanks for replies, useful info indeed and lots to chew over! Thanks, I just found some on eBay US for about £230 shipped. Obviously there'd be some duty to pay but that's about half what I thought they'd be. Can anyone confirm if the ST2 heads will or can be made to work in oil cooled 'mode'? Thanks Darren
With regards to JE Pistons, be sure to check what rings they have as mine were supplied with chrome based rings that buggered up the Nikasil plating in the cylinders. Nothing wrong with the pistons themselves and I would assume they have other ring options? (if not they are available elsewhere) but just be aware. Re. ST2 heads, obviously they will fit if using ST2 cylinders but not sure how the required mods might affect that? I blocked off the oil feed from cylinder to head and fitted external oil feeds to the camshafts.
Aside from the ignition system upgrade (which sounds worthwhile) I'd say none. To improve on how a road bike performs, this would be my order of priority: Brakes Tyres Suspension Wheels Engine (if there's any money left..)
Indeed and the technical winter project is appealing but it's worth bearing in mind the following: - Bigger valves reduce gas speed and consequently turbulence. - Thermal efficiency is reduced due to larger piston surface area (ie. less of the potential energy of petrol is converted to useful work) - Cylinder friction increases due to larger piston diameter. - Like for like, the piston with a larger diameter will weigh more and consequently have greater inertia. To offset all of these introduced negatives you can increase valve lift and duration (cam profile) and increase the compression ratio but that increases combustion chamber, cylinder head, port and piston crown temperature all whilst using a very limited form of cooling (air/oil). It's a one way street. Fine in racing where the engine will be rebuilt routinely but with a road engine all it does is introduce potential unreliability. To run an engine harder the two biggest changes you can make are: - Reduce stroke length whilst increasing bore diameter as this allows you to increase the rpm threshold by lowering mean piston speed and maximum piston velocity. - Water cooling. If you want to do the winter project thing and improve engine performance reliably; sell the high comp pistons and ST2 engine and blue print your existing engine. Maybe give some thought to fitting lighter pistons (with standard CR) and Carillo rods. Then rebalance the crankshaft. Then you're into reliable win, win territory. Less piston inertial mass (and consequently force). Greater pickup and responsiveness as reciprocating and centrifugal mass (and inertia) is reduced.
Hi All, Thanks again for the replies, some really useful info there. I didn't know about that some M900 engines came in 'detuned' form, I found more info on Brad Black's always excellent website and based on the engine numbers it looks like my engine isn't one of them. So with valves the same size as the ST2 there would appear to be no benefit in looking to the ST2 heads. I need to do some more research on the cams, but if what dukedesmo says is correct (and I have no reason to doubt it) then there's little or no benefit unless I switch to split FCRs or injection. FCRs are expensive and since my bike is one of apparently few mainly unmessed with early Monsters - it still has its teatray and original indicators - so I don't want to get into the level of mods required to convert to injection. In my parts stash I also have a M600 frame, and a plastic tank from a later injection Monster and some TBs from a 900SSie, so another option was to build an injected early Monster around the ST2 engine, then I could go crazy with the mods and not feel guilty about the M900. I think I've made my mind up... Thanks Darren
It's obviously a personal choice, but I have a 900ss and a 999..I wouldn't think of any mods for them... I bought a piece of shit 900ie purely so I could play around with a project..if it ends badly then I won't consider it a loss...it's more for the fun of the project! Good luck! Grant
