Hi Mike, It will have a st2 crank(longer stroke) 916 conrods etc will the 748 heads make it have to high compression ?
I may have what you are looking for, i certainly have the heads, i also have a selection of pistons and barrels. you realise that the longer stroke will kick the piston up out the top of the barrel? i have a selection of custom base gaskets to fix this. alternativley, i do have a pair of sps barrels, these are 98mm bore on the small 916 stud patten, these would not be cheap (rare as hens teeth) The heads i have have been rebuilt, valves lapped seats dressed where needed and shimmed ready to go on. i do have 996 heads and barrels also.
Hi Spike, I found a full ST4 top ends going for a bargain so bought them. (I will fit 916 heads with all the st4 drop cam heads bit fitted at a later date which i'm collecting from Mr R sometime) I'm aware of the extra 1mm higher up the bore problem... I will be setting the squish etc.... I would be interested in the base gaskets. I know the later thin head gasket problem was over come on 748's using 1mm base gaskets. I can use the 1mm base and the earlier head gaskets.. Brad the biker boy has written a good article on the 851/888 forum about using a ss/st2 crank.
If i can help with the gaskets i will, the sizes are .9 to 1.5mm, i had these laser cut to order. as for the st4 i thought these were 996 not 916 so have the wider stud patten. i do also have a new pair of ferracci stroker pistons with the correct amount removed to solve the problems. i have built these and at 1026 they are a torque monster.
Hi Spike, The ST4 is 916 ST4s is 996. Here's the post from brad.................. a few points: the 6 spline 900ss cranks - 90 -> 92 - are all narrow, 12mm shorter at the alternator end than the 4v cranks. the only 6 spline long alt snout cranks are 906/907. you can make the narrow ones fit with a wide alt cover bearing i'm told - i know one guy who has done this. the narrow cranks do go into the up to '97 600 and 750 motors tho. use 916 pistons - that will mean your pistons are only 1mm too tall in the compression height, not 2mm. as the pistons are usually .3 - 0.4mm too far down the bore anyway, you can easily get the other mm covered by using some of the 748 specific 1mm thick base gaskets instead of the original 0.3 or 0.4mm gaskets. they are the ones to fix an early 748 with the late head gaskets, and are an official part. last time i checked, nfi had them in stock. # at work if you want it. this works with the std fibre 1.3mm head gaskets - 78610055A. if you want to run the late 0.5mm steel shim gaskets you'll need some custom base gaskets around 1.8mm thick. if you do use 888 pistons you could machine an offset 1mm deep outer ring off them, centred under the spark plug/centre of the chamber ( which is not the centre of the cylinder) so that you have a 1mm dome in the centre. it'll give you a bit more comp. you'll need to deepen the valve reliefs tho i'd think in 888 pistons, but not 916. depending on the timing you want to run, of course. you could also machine the 916 pistons with a similar offset outer ring, but that way you don't get to raise the heads. i like to do that to ensure good belt tension.
Hi imola, i have seen the post from brad on his site and have spoke to him on various other subjects so i know his work, as for his comment on the cranks, this gets a bit confusing as he is talking about the real early cranks when he mentions the 6 spline type, these were NEVER fitted to the 888 or 916, certainly not the 996, so why would you want to fit one? the next series had a multi spline end for the flywheel whilst keeping the single phase alt, these were late 851, 888, 916 and 916 sps (996), not forgetting 900 ss st2 and monster. from 97 there was another changeover when the three phase alt was introduced, these cranks were the same width, later cases were slightly wider on the bearings but this was taken up by thick shims on the cranks. so... you have no worries about the crank fitting. i agree about the shims, i have only yesterday set a 900m up with JE pistons and needed 1.1mm from the base of the barrel to bring the squish back to .95. the comment about 888 cylinders is misleading as the plug is in the centre of the bore, as is all the other 4 valvers, i would be very wary of macining anything off the piston without prior checking of the squish and comp ratio, bearing in mind the compression seems to be no where near the quoted compression and thats before you have messed with the squish, then you are going to alter the stroke, this will radically alter the compression. you need to check this first/last. i cannot see any merit in going with an ultra high comp on a road bike or even race unless you are looking for maximum power and minimum longevety, its probably only worth about 2-3 hp at best with starter problems fuel problems and every thing else inc exess heat that is associated with high comp. finally, you need to be aware that the cam timing will change due to the differing heights of the combo, i would not worry too much on this if max power is not your goal, there is plenty of piston clearance provided the cam timing is not wildly out, i dont think you would notice but it needs checking first ime round. i will pm re the stroker pistons, the price i feel is good considering the price of new rings from ducati.
Hi Spike, Not using a old 900 crank, I'm using a very good ST2 complete bottom end which the crank now has 916 conrods fitted awaiting the st4 top end. Thanks for the advice etc i will let you know how it pans out. You wouldnt by any chance have a 888 front subframe for sale ? Cheers
No go on the subframe, but a word of warning, due to the stroke differences and rod length differences the balance points of the crank assembly is different, hope you are aware of this, also if you are taking metal off the pistons this needs your attention, i can show you the busted crankcases we got due to a small imbalance, just hoping you know this, good luck with the project.
The SPS 98mm barrels interest me............they could be fun on my 853R/RS motor............. Pm me a price if you fancy selling. Mike.
