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Engine Questions

Engine Questions

Postby 72Combat » Wed May 07, 2014 2:20 pm

My Engineer mate and I have just finished putting together an experimental 1000 BMW motor to replace the 900.
The idea was to use as many stock parts as possible as they were around and have some fun
machined 3m off the base of the cylinders.
machined a 1.5 mm squish band in the piston crown.
Image
This has been done following the process given by a successful German tuner.
K line liners and a 3 angle valve job
stock 308 cam
36mm Dells
Ignitech

A couple of questions?
My engineer mate says rings don't need gaps at 120degrees as they rotate.
The nikasil bores do not need any deglazing
rings do not need oiling just a bit on the skirts
He says start it up run at idle for minimum time and then load it up to bed the rings in.

Obviously it works as thats how we did the last engine, how come not every one agrees on that process?

Should be interesting to see in a couple of weeks how it compares on the track to the old 900 that has a 336 " sports cam" and 1mm off the heads.
Hoping for more midrange and punch out of corners as thats where the Brit bikes have it.
The 336 cam had bugger all below 4000, and just comeing on strong when the rev limiter kicked in at 8000.
72' Combat
78' Ducati Darmah
73' R90 Race Bike
80' Moto Guzzi Lemans
74' R90s
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Re: Engine Questions

Postby Triton Thrasher » Wed May 07, 2014 2:42 pm

72Combat wrote: how come not every one agrees on that process?
.


Because it's not in the manual.
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Re: Engine Questions

Postby acotrel » Wed May 07, 2014 3:25 pm

'The 336 cam had bugger all below 4000, and just comeing on strong when the rev limiter kicked in at 8000.'

I'd want it to come on strong well before that. I think you need at least 1500RPM of strong urge below the rev limit, depending on the gearbox. You need to at least catch the bottom of the maximum torque on every gear change, for maximum acceleration. It might be worth doing a rethink on the exhaust system, and the cam timing. I think a race cam in that sort of motor should come on really strong at 4000 and start to drop off at mid 7000s.
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Re: Engine Questions

Postby 72Combat » Wed May 07, 2014 4:28 pm

yes, using the stock cam for a test. On the pre 81 heavy flywheel ones the engine protests much about 6k, the later ones with just a clutch carrier/ring gear rev out nicely to red line.
Hampton Downs does not have the long straights that Puke had.
Its all theory at the moment so a few races soon will see.
The Brit bikes would pass me on slow corners and that was that.
72' Combat
78' Ducati Darmah
73' R90 Race Bike
80' Moto Guzzi Lemans
74' R90s
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Re: Engine Questions

Postby acotrel » Thu May 08, 2014 12:33 am

I would have thought a commando flywheel is as heavy as they come in a motor up to 1000cc. In many motors lightening the flywheel makes them slower. My 850 commando is extremely responsive with the close box. If the ratios are too wide, down-changes can be a problem if you want to ride super-smoothly. I just don't expect the motor to spin up quickly with a wide ratio box, on the way up you are often trying to pull from too low in the rev range. With your BMW, do you have a close 5 or 6 speed box for it ?
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Re: Engine Questions

Postby acotrel » Thu May 08, 2014 12:39 am

I got a bit irritated yesterday when I bought a copy of the new Restos & Classics magazine. There was an article about the XR69 replicas Everett is making. The article didn't mention the gearbox or the cams being used, so was pretty useless. The original XR69 had a 6 speed close box and race cams, two valve motor, I suspect the replicas go nowhere near it - probably 5 speed wider ratio box , four valve Katana motors. That's OK, but why call the game 'historic racing'. It is why I get upset about eligibility rules. I think they've lost the plot.
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Re: Engine Questions

Postby X-file » Thu May 08, 2014 2:34 am

72Combat wrote:The 336 cam had bugger all below 4000, and just comeing on strong when the rev limiter kicked in at 8000.

I'm not surprised.The 308 cam has 240 degrees duration at 2mm valve lift.
If the the 336 cam has 264 degrees at 2mm valve lift,it would be fine for making max torque at 7200 rpm.That would only be good if you could keep the engine running between 5700 and 8700 rpm.

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Re: Engine Questions

Postby Bernhard » Fri May 09, 2014 6:55 am

I do not know much of BMWs but I do recall that Difazio Motorcycles build a BMW using mainly stock parts from the BMW catalogue that was in a bike mag a good while ago.
Try contacting them :?:

http://cybermotorcycle.com/euro/brands/difazio.htm

http://www.somerset-information.co.uk/d ... ?listid=96

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