New 336° cam from BMW

[DanMay]

Originally Posted by AntonLargiader

To me, a 1070 kit with Mikunis would look [sort of] the same as an R50. Close enough!

Ha ! I wish. I run in AHRMA Production Lightweight , and I must keep the same stroke and bore (plus a small overbore is allowed). I am running the R50/R60 /5/6 Bings, those are the only allowed carbs. Then again, you know all this because I believe you have built a R75/5 AHRMA racer in the past...

There is not a lot of information on making the R50/5 go fast and keeping it a 500cc. Most just suggest putting a 600 or 750 top end on it. That is fine for the street, but I need to keep it 500cc and production looking from the outside. A lot of questions:

Will the 600 heads work ? Or will the valves hit the cylinder walls ? What is the best valve size for the 500 ?
What is the best cam profile for the 500cc displacement ?
What is the best way to raise the compression ? Dual plugging is not an option so I am worried a piston with too much dome will not provide an efficient burn on a single plug.

So many options, so little time…

Daniel

[bmwrench]

Using heads and/or cylinders off a 70.6mm stroke motor won't work on an R45/R65 case. The difference in stroke makes developing a decent compression ratio difficult. If you are going to use the R45 cases and crank I suggest using the stock heads with valves from an R65. Bore to 1mm oversize; you can get pistons from a number of aftermarket sources.

On the other hand, you could really cheat, taking the motor out to 750cc. As long as you don't look significantly faster than the other bikes, or win too often, no one should ask for a tear down

[DanMay]

Originally Posted by bmwrench

On the other hand, you could really cheat, taking the motor out to 750cc. As long as you don't look significantly faster than the other bikes, or win too often, no one should ask for a tear down

I need to keep it legal, 500cc max. With a R50/5 bottom end, pistons, and jugs, can you use R60/5/6 heads ? Would the larger valves help or hinder the performance ? Or would it be better off sticking with the R50/5 heads and just do a good port job ?

[Voltaire]

Originally Posted by bmwrench

Using heads and/or cylinders off a 70.6mm stroke motor won't work on an R45/R65 case. The difference in stroke makes developing a decent compression ratio difficult. If you are going to use the R45 cases and crank I suggest using the stock heads with valves from an R65. Bore to 1mm oversize; you can get pistons from a number of aftermarket sources.

On the other hand, you could really cheat, taking the motor out to 750cc. As long as you don't look significantly faster than the other bikes, or win too often, no one should ask for a tear down

Yes.
Its an R65 with 450 cylinders and pistons, finding the 450 kit was hard enough and they were never imported to down under.
Where can i get oversized pistons?
cheers

[Voltaire]

Originally Posted by AntonLargiader

To me, a 1070 kit with Mikunis would look [sort of] the same as an R50. Close enough!

look the same but with the correct capacity, and no Jap parts are allowed.

[Padmei]

Originally Posted by mendoje

I have a lathe, all the right measuring tools and instruments, and I'm ready to plunk down my card to buy one. Referring to this sketch, at the peak of each lobe, we're looking for taper from back to front across the face, right?

Thanks for that Mendoje. I (& prob others not so engineeringly minded) now understand what the discussion is about

[motu]

Originally Posted by supershaft

Piston speed is super safe until you are real close to 9000rpm. If your valves aren't floating and they shouldn't be with titanium spring retainers, rev it higher for more power. If it isn't making more power up there you still might be able to use the over rev to your advantage at some tracks. 336's have good usable over rev.

Revs - I've been lead to believe it's a bit unsafe to rev an Airhead too high, but my R65 loves to spin to 8,000rpm. I use it as an over rev when I have runaway wheelspin on gravel roads, better to let it go than risk an upshift or back off in a powerslide, but also when the red mist is down and shifting by ear, my shift point seems to be 8,000rpm. I've been reading about the Michel 850 kit for the R65, and they say it spins to 9,000rpm. So long as I have no valve bounce, is it ok to run them at these revs ?

It reminds me of the Honda XLV750 I had - max hp at 7,000, red line at 8,000 and limiter at 8,250. I had that bike on a dyno a couple of times and the power curve was exactly the same a Honda's - it only lost a couple of hp between 7,000 and 8,000rpm. I used the over rev on gravel too, but also to save wasted upshifts between corners on the road - let it spin out to 8,000 and then into the next corner. I'd like to do this with the R65 too.

[bmwrench]

Originally Posted by Voltaire

Yes.
Its an R65 with 450 cylinders and pistons, finding the 450 kit was hard enough and they were never imported to down under.
Where can i get oversized pistons?
cheers

I hadn't though about the fact that you're in New Zealand. Venolia (in California) has made plenty of R65 pistons, so they could make some for an R45.

I've never had an R45 apart, so I don't know what the chamber or piston dome are like. Got any specs?

[supershaft]

Originally Posted by motu

Revs - I've been lead to believe it's a bit unsafe to rev an Airhead too high, but my R65 loves to spin to 8,000rpm. I use it as an over rev when I have runaway wheelspin on gravel roads, better to let it go than risk an upshift or back off in a powerslide, but also when the red mist is down and shifting by ear, my shift point seems to be 8,000rpm. I've been reading about the Michel 850 kit for the R65, and they say it spins to 9,000rpm. So long as I have no valve bounce, is it ok to run them at these revs ?

It reminds me of the Honda XLV750 I had - max hp at 7,000, red line at 8,000 and limiter at 8,250. I had that bike on a dyno a couple of times and the power curve was exactly the same a Honda's - it only lost a couple of hp between 7,000 and 8,000rpm. I used the over rev on gravel too, but also to save wasted upshifts between corners on the road - let it spin out to 8,000 and then into the next corner. I'd like to do this with the R65 too.

Exactly! That is what usable over rev is all about. It is very often very handy to reduce lap times! I haven't figured R65 average piston speed per second. The rest of the bikes at a 70.6 stroke are under 4000fps until just short of 9000rpm. IMO there is no need for a shorter stroke than 70.6 since the valve train is the limiting factor at that stroke, let alone a shorter one. Plus the bore to stroke ratio of a R65 is already 1.33:1. The same as a R100. That's already quite the short stroke considering our head design!!!! Any shorter bore to stroke ratio is barking up the wrong tree IMO.

[motu]

I just calculated it all out, and then lost it all....should've written it down the hard way. Anyway, my final point was that bore/stroke is about piston speed, and you can't compare a 650 to a 1,000cc engine....better to compare the R65 to a Triumph 650. At 7,250 the 82mm stroke Triumph has a piston speed of 19.8 m/s, or 3900 ft/min. The 61.5mm R65 is doing 14.86 m/s or 2925 ft/min, at 8,000 the R65 is 16.4 m/s or 3228 ft/min, at 9,000 18.45 m/s or 3631 ft/min.

At 9,000rpm the piston speed of the R65 is lower than the Triumph at 7,000rpm - and the Triumph was considered to be a revver in it's day.

[supershaft]

Originally Posted by motu

I just calculated it all out, and then lost it all....should've written it down the hard way. Anyway, my final point was that bore/stroke is about piston speed, and you can't compare a 650 to a 1,000cc engine....better to compare the R65 to a Triumph 650. At 7,250 the 82mm stroke Triumph has a piston speed of 19.8 m/s, or 3900 ft/min. The 61.5mm R65 is doing 14.86 m/s or 2925 ft/min, at 8,000 the R65 is 16.4 m/s or 3228 ft/min, at 9,000 18.45 m/s or 3631 ft/min.

At 9,000rpm the piston speed of the R65 is lower than the Triumph at 7,000rpm - and the Triumph was considered to be a revver in it's day.

At 8400rpm a R100's piston speed matches a Triumph 650's average piston speed at 7250. My point is that the valve train which is almost identical between a R65 and a R100 is at its limit well before piston speed is on a R100, let alone a R65. The valve train is the limiting factor in both engines. Since piston speed is really not the issue with airheads, why not run as much stroke as you can for more torque. IF piston speed was an issue before the valve train, I would be looking to run a shorter stroke than 70.6mm but . . . .

[motu]

Valve train has always been the limiting factor with pushrod engines, that's why ohc is now the prefered option. But plenty of pushrod engines can be made to rev well, some even stock. I used to rev the unit 500cc Triumph twins to over 10,000rpm, completely stock. So if it's happy at 8,000rpm with no valve float issues, that's still safe on these engines - the bottom engine is up to the task ?

[Voltaire]

Originally Posted by motu

Valve train has always been the limiting factor with pushrod engines, that's why ohc is now the prefered option. But plenty of pushrod engines can be made to rev well, some even stock. I used to rev the unit 500cc Triumph twins to over 10,000rpm, completely stock. So if it's happy at 8,000rpm with no valve float issues, that's still safe on these engines - the bottom engine is up to the task ?

Was thinking the same thing ... lighter stronger materials are now being used in Triumph valve trains, the Trident owner at the track was horrified when I told him BMW ones were nearly a foot long..... he gave me some places that make custom ones in the States that don't flex.....mind you how long is Triumph one...4"....?

[pommie john]

Originally Posted by motu

Valve train has always been the limiting factor with pushrod engines, that's why ohc is now the prefered option. But plenty of pushrod engines can be made to rev well, some even stock. I used to rev the unit 500cc Triumph twins to over 10,000rpm, completely stock. So if it's happy at 8,000rpm with no valve float issues, that's still safe on these engines - the bottom engine is up to the task ?

The main issue with high RPM in airhead engines has been cavitation at the oil pump. Essentially, the pump is trying to suck too much oil from the sump and it has so much suction that it causes bubbles to form in the pick up tube. The traditional way around this was to drill the pick up out bigger. ( I think it goes from 10mm to 13mm but one of the other guys will correct me if I'm wrong).

After doing this to my racer, it's happy running to 8500 with no problems. I have an oil pressure gauge just in case.

I believe some people have machined the pump thinner so it draws less oil.

I'm not familiar enough with the R65 engine to know if it's a problem with them too.

[Rob Farmer]

Originally Posted by motu

Revs - I've been lead to believe it's a bit unsafe to rev an Airhead too high

Moorespeed engines rev to 10,000 rpm and seem to be very reliable. If you look at the website under the 750cc class theres a brief lowdown on the moorespeed short stroke engine.

http://www.moorespeed.co.uk/classic-racing