griff851
While changing my old 851 rails over to the new modified 748 TB's today, I noted this little conundrum The vacuum lines that go to the pressure regulator on the early TB's provide for the fuel pressure to drop during high vacuum events ie idle and throttling down. Meaning also that the pump is in a more relaxed state as well. When vacuum decreases the spring is then providing more force on the diaphragm as the air pressure increase in the spring chamber thus loading the pump up and provide full fuel pressure to the injectors when they need it most. Later throttle bodies don't have this wonderful resource. If you just leave the air port open to atmosphere on the Pressure regulator, you'll have trouble getting over Alps and such (Not many Alps around these parts), as fuel pressure will drop off the higher you go. If you just seal it up you run the risk of moisture build up inside the spring chamber. The easy solution would be to up the fuel pressure to the high end of the settings, 51psi (3.5 bar). If you had it at 44 psi (3 bar) at 2000ft you would only get 43psi. At 5000ft you would only get 41.5psi. At 10,000 ft a paltry 39 psi.
The other solution I thought of, is running a line from pressure reg vacuum port to the Inlet manifold ports that you connect vacuum gages to. The early manifolds have a port on each side which is handy.
I'm also going to make up an Aluminum fuel line to connect the TB to the Inlet of the pressure reg. Too much of a nasty turn for the rubber fuel line.
I threw in a pic of my handy dandy collett seating tool in action.
Henrik
griff851 wroteWhen vacuum decreases the spring is then providing more force on the diaphragm as the air pressure increase in the spring chamber thus loading the pump up and provide full fuel pressure to the injectors when they need it most. Later throttle bodies don't have this wonderful resource. If you just leave the air port open to atmosphere on the Pressure regulator, you'll have trouble getting over Alps and such (Not many Alps around these parts), as fuel pressure will drop off the higher you go. .
Being more theoretical that practical I can't resist to debate..
The 3 bar standard pressure from the regulator is 3 bar above atmosphere. Thus the spring force divided by the area of the diaphragm gives 3 bar, then there is one more coming from the air behind the diaphragm. When you go over the alps you will still have the 3 bars from the spring but the atmospheric pressure will decrease giving less pressure feeding fuel. But the pressure on the other side will decrease by the same amount (in the manifolds) thus giving constant delta pressure and constant amount of fuel per millisecon opening time. So, if there was not a pressure device telling the ECU that you are going over the alps you would have to much fuel since the air gets thinner.
At least I think that's the way it goes?
The best solution might be to skip the theory and go to the Alps for a real life test?
Henrik
griff851
Ah but does the manifold pressure decrease by the same amount. The air pressure sensor tells the ecu that there is less air so leans out the fuel. There is a big difference in static pressure and dynamic pressure.
We have no alps here so I can't test this. So we need a brave volunteer to take a set of mercury vac gauges up the alps or nearest local equivalent and check it. ๐ Anybody with Alps nearby, not doing anything this weekend.๐
Griff
Millihaff
griff851
Well arn't MBP collets fun. My little tool for pressing the collets into the shim, needed a quick redesign and I machined up another. It needed side walls to stop the feet bending. Once that was sorted the process seem to go along quite well, I got 2 exh closers done last night. I was going for the lower of the manufacturers tolerances which are quite large for droop cam heads. Exh are 0.08- 0.13. ( I got 0.10 ) I don't know whether its worth trying to go to 0.08 0.001" is not really all that much The Inlets are are massive at 0.13-0.18 mm. and are today challenge.
Griff
marvin
Griff,
Yep, lots of fun!! ๐
But, once you're done, you're done! Just think about how much fun it is to do the valves with the engine in the bike! You won't have to do that very often from now on!!
griff851
I finished one head completely last night and most of the second. I had to grind down a closer to 2.3 and another to 2.4. Man it takes a while to get them perfectly flat. You install the shim,rotate and check between the fork arms, then remove and grind on 600 grit. The main griding is done on the side of the grinding wheel. I did order 2 closers, but couldn't wait as they have to come from Italy. While I was ordering I noticed that 1098's now use a Ubeaut collet. i didn't get a price I will do that today, but they don't need modified openers. I fucking hate that when you finds stuff after the you've just done something.
I set the heads to the head to:
Inlet open 0.15
Inlet close 0.15
Exh open 0.18 (loose)
exh close 0.10 (tight)
The numbers are bigger than 851/888 due to different thermal expansion
ST4S S4 748 droop cam head and cams manufacture specs
Open int 0.13-0.18
exh 0.18-0.23
Close int 0.13-0.18
exh 0.08-0.13
Griff
griff851
Just got a price on the 1098 collets. About AUS$340 a complete set.
Griff
brad black
the different valve clearances are just the wider ranges used in the later engines to reduce the need for adjustment. the actual head itself is the same pretty much, i don't really understand why you've gone to the trouble of using them.
griff851
Many reason Brad, the tinker factor being high on the list I guess. First thoughts were it was easy way to increase compression. The heads were ridiculously cheap and that helped. The heads have 12 years of development over the 851 ones I have, and one would hope the boffins at Ducati are moving forward in that dept. so as they are the last desmoquattro development they should be the best. And I guess it's just a bit different. My initial reason to upgrade to 888cc was I just wanted some more torque, but as usual things just get away from initial concepts. Lots of 'what if I justย
.ย Now I'm going to have a lightened fully balance ceramic coated whoop arse machine if I'm lucky and planned it right.
As for the larger shim clearances, you're right about the standardization. I made an assumption based cases material changes that took place and the changes I noticed in workshop manuals I've been looking at. I thought they happened around the same time therefore and ergoย
. After chatting to Bob about it he said he believed it was because the gaps were initially tight and worked, but people taking every thing as close as they could to lower tolerances resulted in colletts ( half rings) being broken, so Ducati decided lift them, and now give larger assembly and running tolerances. So hopefully people will set them as close to the middle of the tolerance range and all should be well, and the servicing interval is longer as you mentioned.
I only set my exh open shims to the lower end as I made a whoopsy before sending them to Marvin. They are a loose 0.18 (probably 0.195 max, but not 0.20) as I gave them a bit of 600 grit, but being small with a little edge, my fingers started to ping just a bit too much.
PS the Ducati Catalogo is wrong (not the first time) The 1098R has the U beaut colletts but they run a thinner valve stem according to the young feller.
Griff
brad black
the development on the heads would have been to fit applications - there's no difference in the heads from early 748 to late 748 and in general from 851 to 996. with the last run of 996 motors in 2001 they were making 3 different head castings - old large exhaust rocker cover 748, small exhaust rocker 996 and dropped cam s4/st4/st4s. when they dropped the 996 they were left with 2, and someone obviously said "why are we making this unique 748 head" and that was the last of the old style. it's only a cnc program difference anyway from s4 to 748.
not that i'm having a go at you, you just seem to have this "must be better opinion" about the later stuff, when it's just the same. certainly smaller chambers are better, but the old 748 heads go on and all you needed is blanks sort of thing.
griff851
I can see what your saying there Brad, the 748 droop cam has the smaller chamber that is a more "V" shaped combustion chamber, and the ports are different to my old 851 elliptical hemispherical head. Is not that better and a development?
Griff
marvin
Griff,
Did you unshroud the valves on those heads?
griff851
Sure did, I used the information that I got from that porting school webpage I posted somewhere.
Griff
brad black
the chamber and ports are the same on the '95 748 heads, and it's not a development as much as a requirement - smaller chamber for the smaller engine. the valves sit higher in the 748 heads due to the smaller chamber requirement, so overall it looks a lot smaller and more compact.
speculating, they may also have gone with such a small chamber as they were developing a long duration cam version and knew they needed deep valve reliefs in the pistons so needed a small chamber to help keep some comp.
much like the later shorter duration inlet cams - they were fitting them to two "new" engines, one which was set up to not produce top end power as delivered (s4, small headers) and the other being fitted with single instead of dual injectors per cylinder and so possibly needing to be restricted after the power peak (st4s). and it worked as well or better than the previous cam anyway below the power peak. if it hadn't been for those two constraints they could have just used the sps cams. i wonder if any of their durability testing showed diminished reliability with them. they certainly go as well from idle to red line.
or produce another exhaust cam that wasn't so assymetrical and more like the sps cam.
griff851
Back again campers, Engine cases should be together by now, but I had a small hold up. I was missing one bearing retaining clip for the belt drive layshaft bearing, and no where near enough Threebond. So I machined up the 5mm spacer for the front sprocket instead. Its a nice profile same as the locking plate.
As part of the paper gasket to Three bond gasket, I ran the file around the joining surfaces to gives nice flat square edges , cleaned them, and clamped the cases lightly. I gave the shafts a spin and the selector drum a cycle through the gears....... Awww sweet as.๐ Feels fast...
Wednesday now for final assembly of the cases and maybe barrel base gasket time. Thursday, primary gears, and alternator shaft stuff, gear selectors and oil pump with a bit of luck
Griff
griff851
Ah the classic fuck up. I put the cases together today. Very carefully laid a 2mm bead of Treebond around the edges, lowered the cases carefully,and put in the bolts in and torqued them up. Checked the gear selection, and rotated the crank. Very free. Mmmmm. Get Bob to have a feel. He gives me some shit about it being 0.03, definitely not 0.08 or 0.05. I do and end float check. 0.02 end float. Damnation and cussing. What the hell happened. 0.5mm out either side. Ah... I should have been grinding a 1mm not a 0.5. Good news is tomorrow I'll pull them apart and just bang in 1mm either side and be done with it. Well...I might shave off a poofteenth, to get 0.08.
How did it happen. Bad recording of data. I divide my end float but didn't annotate per side on my scribble sheet, a couple of days later I looked at the scribble sheet divided by 2 and went for it. This weeks dick head award goes to....
Griff
Mr.R
Been there and done that Griff so your not alone mate.
Years ago whilst working at the shop I stayed late to finish a Bevel bottomend off.
I was still working when a workmate was leaving for home, he left me a spliff...
I put that bottomend together 3 Fuc*ing times before giving up for the night!
Came back in the morning and within a hour she was all boxed up and ready to drop in the frame.
Steve R
griff851
Ah another day of playing. i completely screwed up that last thread. I need 0.55 a side to get 0.1 crush. You'll have to forgive me I got shot up with Zometa yesterday. Its a drug to stop my bones leeching calcium, which is a side effect of the anti cancer pills I'm on for the next 10 years. Not only is life a bit confusing, but I managed to have every bone in my body aching like a bastard, as Calcium is forced out of the blood and shot into the bone chemically. Very amazing stuff really. All this, so should I fall off the bike, I won't shatter. Cool hey
Anyway I managed to do deck heights. No barrel base gasket and I get about 0.7mm mill from the piston to the deck, with the 0.45mm (0.018")gasket, that makes a swish band height of 1.15, So whats the go here if it goes too big, and how big is too big? I know 1mm is the ultimate target. What is a standard 888 with that huge fat gasket? I.3mm I think somebody mentioned as the gasket thickness.
Griff
Mr.R
Griff,
I've played with squish settings for many years, I've always excepted the general rule that anything over 1mm and it's not going to do the job it's intended to do.
On smaller capacity motors (Yamaha 2 strokes etc) I've gone as low as 0.5mm.
I set the squish on my 851/916 at 0.9mm, I've heard of guys going as low as 0.75mm and that was on a 748 raced at Daytona.
On stripping the motor after the race nothing had touched, the guy did say that he had his fingers crossed throughout the race though.
If I were you I'd aim for 0.9-1.00mm which's tight enough to do the intended job with a good safety margin.
If you can't get in the zone using gaskets, then it's on the lathe with the barrles and turn them down.
With this squish I'd use SuperGreen fuel though.
Steve R
