Topic: CB750 1000cc RC Cobra Rebuild

[MRieck]

Well if you think the rods are too expensive, the spacer under the cylinder block is out of the question, then what in the hell is the use of a stroker crank ?  
I guess you would have to order some custom stroker pistons and what would the cost of those be compared to the
carrillo rods ?

I didn't mean to sound so contrite......a stroker is a nice means of getting displacement as long as the rod angle doesn't get ridiculous. 5mm would be great....M3's cam chain tensioner may be the ticket for dealing with the needed cam chain length.....it doesn't seem to take up as much free chain length.

[BLUE71TURBO]

Well if you think the rods are too expensive, the spacer under the cylinder block is out of the question, then what in the hell is the use of a stroker crank ?  
I guess you would have to order some custom stroker pistons and what would the cost of those be compared to the
carrillo rods ?

I didn't mean to sound so contrite......a stroker is a nice mean so getting displacement as long as the rod angle doesn't get ridiculous. 5mm would be great....M3's cam chain tensioner may be the ticket for dealing with the needed cam chain length.....it doesn't seem to take up as much free chain length.

Oh hell no! You didn't sound contrite. I just get a little discouraged about trying different ways to build a big cb750
motor and ya hit a brick wall. It's not like the old day's when bigblocks, various large piston kits in all comp. ratios
were available. I guess these kind of parts just aren't in that great of a demand. Like the big blocks your trying to make.
By the way, how's your project comming along ?  I'd really would like to see how the bigblock look's like !!

[MRieck]

Well if you think the rods are too expensive, the spacer under the cylinder block is out of the question, then what in the hell is the use of a stroker crank ?  
I guess you would have to order some custom stroker pistons and what would the cost of those be compared to the
carrillo rods ?

I didn't mean to sound so contrite......a stroker is a nice mean so getting displacement as long as the rod angle doesn't get ridiculous. 5mm would be great....M3's cam chain tensioner may be the ticket for dealing with the needed cam chain length.....it doesn't seem to take up as much free chain length.

Oh hell no! You didn't sound contrite. I just get a little discouraged about trying different ways to build a big cb750
motor and ya hit a brick wall. It's not like the old day's when bigblocks, various large piston kits in all comp. ratios
were available. I guess these kind of parts just aren't in that great of a demand. Like the big blocks your trying to make.
By the way, how's your project comming along ?  I'd really would like to see how the bigblock look's like !!

The blocks are coming....it was/is a money thing....start up isn't cheap.  I'm committed to the project and will be speaking with the CNC guru next week....hopefully is still up for it.  Hell...the world is going to end in 2012 so whats a few bucks guys.

[MRieck]

 Jay is right...that 1000cc kit, 5mm stroke, billet block....that would be killer....especially torque wise. It would surpise the crap out of kids on modern bikes.

[bear]

[/quote] It all comes off of some shelf. RC45 pistons?....that isn't cheap. They sold about 100 RC45's of them in the USA. so they aren't a junkyard item. I have no problem missing and matching OEM parts but sometimes it is reinventing the wheel (which takes a lot of time). Shorter rods for strokers is easy..... Carrillo has them on the shelf for busa's......it's just expensive. You should see the heavy duty primary chain sets for the 750....better than than the CR chains. I sent 2 sets to a fella in Great Britian so I know there are some over there.
[/quote]

No RC45's made it to Oz but I can buy pistons for $55 a pop, that's about $1 American and believe me their good gear.
As for time and money, well I can always scrounge the time but she who must be obeyed is pretty tight with the purse strings when it comes to my "toys" as she calls them.
Bottom line is, we're running two of these motors now.
The 1140 is a beautiful thing and has given us two seasons of trouble free racing.
The 1260 has been a bit of a problem child. Keeps popping head gaskets. But we're working on it.

Cheers,
Brian

[moham]

It all comes off of some shelf. RC45 pistons?....that isn't cheap. They sold about 100 RC45's of them in the USA. so they aren't a junkyard item. I have no problem missing and matching OEM parts but sometimes it is reinventing the wheel (which takes a lot of time). Shorter rods for strokers is easy..... Carrillo has them on the shelf for busa's......it's just expensive. You should see the heavy duty primary chain sets for the 750....better than than the CR chains. I sent 2 sets to a fella in Great Britian so I know there are some over there.
[/quote]

No RC45's made it to Oz but I can buy pistons for $55 a pop, that's about $1 American and believe me their good gear.
As for time and money, well I can always scrounge the time but she who must be obeyed is pretty tight with the purse strings when it comes to my "toys" as she calls them.
Bottom line is, we're running two of these motors now.
The 1140 is a beautiful thing and has given us two seasons of trouble free racing.
The 1260 has been a bit of a problem child. Keeps popping head gaskets. But we're working on it.

Cheers,
Brian
[/quote]

I, for one, would love to see some fotos of said motos...

[BLUE71TURBO]

One of these day's i'm gonna learn who to post pictures on the internet. I really would like to show all of you guy's
my turbo bike and all the goodies i have for the cb750's !  I'm just a little behind the current times. 

[Big Jay]

We get $1295 for custom Carrillos. We are a Carrillo master distributor so we have wiggle room. I think there is plenty of room for 6 mm as that was pretty common. There was even some 3/8 floating around.

A 1000 with a 6 mm crank is 1097cc.

Jay

[BLUE71TURBO]

So the cost of adding 97cc's by using a stroker crank - $1080.00 + rods - $1280.00 = $2375.00  above the cost of
the 1000cc pistons and machine work, WOW !!   I hope the big block project works out soon.

[BLUE71TURBO]

HEY BIG JAY !   What is the longest stroker crankshaft you can put in the cb750 cases ? 

[bear]

No worries. Give me an hour or two untill it slows down here. I've got a couple on my phone I think. Just gotta work out how to down load them.

Cheers,
Brian

I, for one, would love to see some fotos of said motos...
[/quote]

[Big Jay]

Like I said, I knew some guys that had 3/8 cranks. Don't know what they had to do to get them in.  By the time we started doing strokers, no one was doing the Hondas anymore. Now there has been a re-newed interest in big Hondas.

As for adding only 97cc, it is not just that, it is the tremendous grunt that 97cc gives you because of the increased leverage at the crank.

Jay

[NitroHunter]

Anybody got ideas for a slightly longer cam chain? I think the SOHC is either 92 or 94 links, adding a couple links would allow for the use of a 1/8"+ base plate...

[michrobi]

Aren't those HD Tsubaki's 96 link out of the box?

[BLUE71TURBO]

You can order longer length cam chain just like the drive chain and use the special tool to smash the pin over.
I had my friend do it for me on a 1132cc kawasaki i built years ago. I didn't want to split the cases, just did the top end.

[bear]

A couple of photos as promised
Pics are from our little motor. Had to pull the top off after sucking in a rock when we put it through a gravel trap a couple of meetings ago.
MRieck,
Sill have the reciept for the ring sets. At $55 a set they are $5 AUS dearer than the pistons. Ordered at our local Honda dealer and supplied two days later.

Cheers,
Brian

[MRieck]

That's cool. Do you machine those yourself or do you throw those in stock for a 2 valve.....I can't tell because the pics are micro scopic and I can't see the pistons.

[JLeather]

Just a heads up, I was chatting with a dude from I believe Texas once who raced midgets with CB750 SOHC engines in them.  Had the trans cut off the engines with a driveshaft setup off the alternator end to a 4spd box and clutch.  Crazy setup.  Anyway, he ran CB900 DOHC rods in his motors.  They're longer than SOHC rods (as per Axel's site) and he ran a spacer under the jugs to make it all work out.  Ended up with a much better rod-angle and he spun those motors way up in rpms, like 12k+, frequently.  His solution for the cam chains was he made his own from #219 shiftercart chain with an extra 2 links or so to make up for the added jug spacing.  I haven't yet validated this (no shiftercart stores in my area) but he said that's what he used.  I was pondering this when trying to come up with a cheaper way to get the compression down for the turbo motor.  If anyone's into shiftercarts, maybe give it a look-see.

These RC45 pistons are very interesting though.

[UJM]

This is a really great thread, thanks everyone, I'm beyond impressed.

[MRieck]

Just a heads up, I was chatting with a dude from I believe Texas once who raced midgets with CB750 SOHC engines in them.  Had the trans cut off the engines with a driveshaft setup off the alternator end to a 4spd box and clutch.  Crazy setup.  Anyway, he ran CB900 DOHC rods in his motors.  They're longer than SOHC rods (as per Axel's site) and he ran a spacer under the jugs to make it all work out.  Ended up with a much better rod-angle and he spun those motors way up in rpms, like 12k+, frequently.  His solution for the cam chains was he made his own from #219 shiftercart chain with an extra 2 links or so to make up for the added jug spacing.  I haven't yet validated this (no shiftercart stores in my area) but he said that's what he used.  I was pondering this when trying to come up with a cheaper way to get the compression down for the turbo motor.  If anyone's into shiftercarts, maybe give it a look-see.

These RC45 pistons are very interesting though.

Yeah the big thing is rod angle. Also....that OEM cam chain tensioner isn't meant for 12,000

[MCRider]

Just a heads up, I was chatting with a dude from I believe Texas once who raced midgets with CB750 SOHC engines in them.  Had the trans cut off the engines with a driveshaft setup off the alternator end to a 4spd box and clutch.  Crazy setup.  Anyway, he ran CB900 DOHC rods in his motors.  They're longer than SOHC rods (as per Axel's site) and he ran a spacer under the jugs to make it all work out.  Ended up with a much better rod-angle and he spun those motors way up in rpms, like 12k+, frequently.  His solution for the cam chains was he made his own from #219 shiftercart chain with an extra 2 links or so to make up for the added jug spacing.  I haven't yet validated this (no shiftercart stores in my area) but he said that's what he used.  I was pondering this when trying to come up with a cheaper way to get the compression down for the turbo motor.  If anyone's into shiftercarts, maybe give it a look-see.

These RC45 pistons are very interesting though.

I have a set of DOHC 900 rods from CycleReCycle. He was marketing them to TQ midget guys, I bought them thinking I might use them someday, never have. Anyone interested in buying?

[Bill/BentON Racing]

Rc Cobra motors usually came w/327 cam,an 836 w/315 was a lot of fun!sounds like you have a Norris reground cam using one of Honda's stock cams to start with.Find the best rods you can the 2 or 3 you mentioned are possibilities,others?,Bill Benton

[BLUE71TURBO]

What would be the best setup for a cam chain tensioner ?  Does someone make a better tensioner ?

[mlinder]

What would be the best setup for a cam chain tensioner ?  Does someone make a better tensioner ?

Companies such as M3 Racing have very nice teflon cam chain tensioners. Run 150 bucks or so.

[754]

I am sort wondering about this all steel camchain tensioner I found in this 69 1080 engine?, anyone ever see one?

Both rollers had bearings, one had teeth..sorta like stockers but steel.