Author Topic: My project, "an updated CR750", far from being done... pics (Read 27272 times)

PhotoGeek · « **Reply #25 on:** October 24, 2007, 11:19:39 PM »

Thanks anyhow Sam, the warning is warning enough,

Not 100% sure 754, I've read on a couple other forums that it can be done, and has been done. From what I gather the front mounts are fine, it's only the rear mount that is about 1/2 an inch off or so. But as I said, I have to have one in front of me or see an actual account of it being done to know for certain. I'll see if I can't find those posts for you.
-peter

Irishguy · « **Reply #26 on:** October 25, 2007, 02:02:39 AM »

Well... For what it's worth I have a complete 1981 CB750 Super Sport DOHC bike in my garage. It's complete and runs, but the carbs need some tweaking and I think it may have a charging issue also. I have ridden the bike as recently as a month ago, but it is on the back burner right now because of my other 2 bikes.

I am considering parting it out, because after riding it, I don't really care for the dynamics of the bike. I don't know where you live, but if you think it is something you might be interested in let me know.

eurban · « **Reply #27 on:** October 25, 2007, 04:23:01 AM »

Sorry to be critical here but . . . . . .Best as I can tell, the cylinder bank on SOHC 750 engine is tilted pretty far forward. Most of DOHC Honda engines I have seen (I am no expert) are much more upright. With a SOHC 750 motor installed in a stock frame there is almost no room between the top frame rails and the valve cover (you have to remove the engine to service the top end) so how's a more upright and probably taller motor going to fit? Have you done any measuring or trial fitting? Seems like there will be lots of cutting, welding and reengineering involved just to fit the engine to the SOHC frame. Also, if you don't change the angle of the front down tubes there will be alot of space between them and the more upright cylinder bank. You are adding very nice suspension components and grippy tires to a low tech flexy frame that will probably have to be hacked up and rewelded. Doesn't sound like a particularly good recipe for a bike that you want to perform as well as it looks. . . .Maybe you have already thought about this stuff and figured out a good plan of attack?

20 minutes later . . .Ok so I found a couple of pics that might be helpful, one of a SOHC 750 from the side and one from a DOHC 750. Tilt difference isn't a big as I expected.

eurban · « **Reply #28 on:** October 25, 2007, 04:35:45 AM »

And the DOHC 750

eurban · « **Reply #29 on:** October 25, 2007, 05:07:10 AM »

And a DOHC 750 frame (which has removeable side rail) . . . .

750essess · « **Reply #30 on:** October 25, 2007, 05:32:17 AM »

Very cool project, What Engine management are you planning on using? I am planning on converting mine to F.I. this winter. Found this company http://www.perfectpower.com/products/standalone.asp that has a stand alone for a reasonable price.

PhotoGeek · « **Reply #31 on:** October 25, 2007, 04:14:55 PM »

I'm in WA state Irish, I'm really looking for one of the black motors, I may be interested for the right price though,

, depending on your location. Thanks for thinking of me.

No worries Eurban, It's good to have other opinions, it keeps you from convincing yourself that something will work when in fact it may not.

This is what I've read on other sites,

So, as creditable as online sources can be (google search led me to "Slicks choppers"), it seems that it is doable with a little mickey mousing about with the rear mounts. I just need to save up and buy some machining equipment,

haha, and then learn how to use it, hahaha.

I have to get the motor before I can start to test fit. Right now it's just a bit of a pipe dream, if it doesn't work, it doesn't work. Though I'll have to try to see. I think you were thinking about the 550's head angle, which is basically upright. The removable sections of the later motor's is another reason I'm not a huge fan of them.

750essess, I'm going to most likely be using Bowling & Grippo's MicroSquirt. It's especially meant for tighter applications such as motorcycles. They're about 400 from DIYAutotune, but you have to buy an external MAP sensor. The Microsquirt seems like a very extensive system; covers all the bases.

It's completely new teritory for me, luckily I have a couple of friends who know their wiring, so I should be able to figure it out through some trial and error... I hope....
-peter

PhotoGeek · « **Reply #32 on:** October 25, 2007, 04:34:57 PM »

eurban, this is the one that gets me all excited, haha.

They come with silver valve and points covers, I love the all blacked out look though.
-peter

Geeto67 · « **Reply #33 on:** October 25, 2007, 04:38:05 PM »

I happen to know of Lady Dr and some of his bike though the net and I am pretty sure the DOHC in the SOHC frame he is talking about is a SOHC CHOPPER aftermarket frame from the 1970s. He used to pop in here from time to time. Without serious modification a DOHC motor will not fit in a SOHC STOCK frame. something to think about, the DOHC frame has drop outs to allow engine removal that the SOHC does not.

Personally I think the SOHC motor is "stouter" than the DOHC motor.

paulages · « **Reply #34 on:** October 25, 2007, 06:25:29 PM »

i certainly don't know the HP numbers, but i used to have a '79 DOHC and thought it had some serious get up and go. i can't say it had so much more that i'd consider the frame modification it would take to fit a DOHC engine in a SOHC frame. maybe i missed this post, but why aren't you using the SOHC engine?

eurban · « **Reply #35 on:** October 25, 2007, 07:25:21 PM »

Those CR carbs do look very slick on that black DOHC motor. They also look pretty nice on a SOHC. Here's a shot from Cyclexchange's site. Lose the finned points cover IMHO tho . . . .

754 · « **Reply #36 on:** October 25, 2007, 08:19:46 PM »

Where in Wa are you? I am about 4 hrs east of Vancouver BC.. too bad you are not close.. I could help you out with machining..

closer than NV but there is a border in the way..

PhotoGeek · « **Reply #37 on:** October 26, 2007, 09:32:55 AM »

As far as HP/TQ goes, I have three differing sources (for an 81):
Wikipedia says, 70hp/?
Motorcycle Specs says, 72hp/67 Nm (which at a conversion factor of 1 Nm = 0.73753 ft·lb, is 49.41451 ft·lbf)
Bikz says, 78hp/?

I was worried about that Geeto, I should have searched that forum a little better, although I have read elsewhere that people have tried it with the same conclusion, the rear mounts need some work, but othewise it sits in there.

This is another post, the opposite, but hopefully the same holds true,

One of the other reasons I've been interested in the DOHC is because the lack, or so I gather (hopefully I'm not wrong here), of an external oil tank on the DOHC. This would also simplify and lighten the bike some.

Yeah eurban, that is a very good looking motor, I have that photo saved on my computer.

I'm in the Gig Harbor area, right across the Narrows Bridge (Galloping Gertie) from Tacoma, and about 45 minutes SW of Seattle, about 40 minutes NW of Olympia. Thanks for the offer 754!

I may take you up on that.

I'll just have to get one and try it, I'll post some pictures when I do.
-peter

jonbuoy · « **Reply #38 on:** October 26, 2007, 08:12:28 PM »

I guess the idea is to get some cost effective horsepower but keep the classic looks of the CR750? With a full fairing you probably wouldn't spot the DOHC engine when its on the move.

MRieck · « **Reply #39 on:** October 27, 2007, 08:37:54 AM »

Quote from: SamCR750 on October 24, 2007, 09:12:48 PM

I can't remember Pete, I just remember them blowing up real easy.

I think there is a forum for them where you can find info on them.

Sam.

Cam chain system is weak.

petescb · « **Reply #40 on:** October 27, 2007, 01:26:56 PM »

Nice work! I'd suggest deep-sixing those shocks, but that's up to you. What's the fairing on the SV650? It's gorgeous.

PhotoGeek · « **Reply #41 on:** October 27, 2007, 06:59:32 PM »

Kind of yeah jonbuoy, I also like the look of the motors, and the lack of an oil tank.

MRieck, is it just the cam chain itself? the tensioner, or...

Haha, Pete, don't worry man, those are going as soon as I'm close to riding the bike, I'm just concentrating on other things for now; a money spent better elsewhere type of situation.

The fairings on the SV are Sharkskinz full street fairings. They took a bit of fitting to get on there, but they were worth it. Luckily I have a buddy that paints on the side.
-peter

PhotoGeek · « **Reply #42 on:** October 29, 2007, 07:56:33 PM »

Not a lot of progress, but i got a 160 rear put on the 4.5"x17" Aprilia RS250 rear wheel tonight. The tire was just sitting around the garage anyhow, it was the original tire on the CBR F3 rear I have on my SV.

It doesn't quite fill it up as much as I was hoping, but I'm not going to go any bigger on this build. It's already 40mm over what it was originally, and one size up on the Aprilia wheel.

No other news than that, bills to pay and so on, haha,
-peter

Sam Green Racing · « **Reply #43 on:** October 29, 2007, 10:08:44 PM »

Hey Lomby, that rear end looks cool but will the drive chain line up ?

Sam.

PhotoGeek · « **Reply #44 on:** October 29, 2007, 10:29:45 PM »

No idea until I get it all in there, if it doesn't, then I'll either figure it out, or fit a different wheel with a 20mm axle.

The cush on the wheel was milled down 5mm by the previous owner, he had installed a KTM 450 motor in his RS250, so hopefully that will either be close enough to the wheel, or if not I'll just align the chain and space the sprocket until it works. I have to get a different sprocket for the rear anyhow, and I'm hoping that I can convert it to a 520, or at least 525 chain.

I just really need to find a motor to get much further. I have a long, long list ahead of me.

I do most of my research, but partially I'm a cross my fingers kind of guy, if it doesn't work there has to be a solution.

Thanks Sam,

-peter

cben750f0 · « **Reply #45 on:** October 30, 2007, 01:57:18 AM »

i have seen modified front sprockets that are indexed 10-20mm maybe that would help?

peace

750essess · « **Reply #46 on:** October 30, 2007, 05:17:07 AM »

Thanks for the link to that injection controller photogeek, it does everything that the one I was looking at does and is smaller and cheaper. I am going to use this one as well.

PhotoGeek · « **Reply #47 on:** October 30, 2007, 09:22:09 AM »

cben750f1, Are you talking about the ones from Cycle Exchange? They're for the SOHC's, and I'm not sure if they'll fit on the DOHC, but it would be a good thing to look into, thanks!

No worries 750essess, I actually saw it in PB (Performance Bike Magazine) on some project they had in the front pages, I believe it was a Mito with a 500 crammed into it and a Ducati tank. The guy was converting it to fuel injection with some, i believe, R6 throttle bodies and that MicroSquirt.

If you get to it before me, you'll have to let me know how it works.

-peter

750essess · « **Reply #48 on:** October 30, 2007, 09:23:43 AM »

I just ordered it.

PhotoGeek · « **Reply #49 on:** October 30, 2007, 09:31:39 AM »

Haha, well your definitely going to beat me to it then! Now you have me all jealous! Haha

-peter

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Author Topic: My project, "an updated CR750", far from being done... pics (Read 27272 times)

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