Topic: Educate me on "The Gentlemen's Express"

[jaguar]

My chop needs a head gasket and I'm unsure of the life the pistons in it now have lived.
Thought about adding a bit more HP to it over the winter.

I have read the article and think it would be fun to run the 750 pistons.
Also I figure it would make a good street engine for the chop too, not looking for screaming RPM and silly peak numbers.  More looking for a well rounded engine.

Few questions.
First, am I correct in thinking that this will give me a good engine for the chop?

From what I read it is better to replace the piston sleeves.

Are all "300" pistons the same?  I have found a few single and double NOS pistons for sale, but they are 300-XXX and the last three numbers vary a bit.  Don't understand Honda part numbers very well.

The article didn't go into the measurements for the valve cuts to the pistons.....

 

[turboguzzi]

the answer to your two first questions would be yes and yes (must put bigger sleeves...)

regardless of the type of "300" pistons, remember that you will HAVE to to turn on a lathe the edge of the pistons flat + the 15 degs thing according to the drawing in the article.

at that point, making a measurement with plasticine to see that you have the right valve clearance would be recommended for sure

[01Thomas]

Hi!
Could someone point me to this article?

Regards
Thomas

[scunny]

here you go
http://forums.sohc4.net/index.php?topic=20601.0

[jaguar]

OK so leaves it is, kinda figure that was needed.
And good to know that all 300 pistons are the same.

Im OK with the lathe work to modify the pistons like the picture.  Just have never cut valve reliefs, but there is always a first.


So about the running characteristics of this motor.....

[turboguzzi]

it will be very torquey rather than revvy, good match for a chop

[70CB750]

Jaguar, are you starting new project thread or is it all gonna be here?  I want to see this.

[RAFster122s]

Finding someone to modify the pistons has been the big issue on this mod for many. Align bore the new sleeves since according to HondaMan and others the cylinders drift out of alignment initially causing a loss of 5-10%, I forget which it was.
Are you going to do the lathe work or have you found someone willing to do it?

[jaguar]

We have a machine shop on campus.
I'm an aerospace engineering student.

Don't think I trust the machines to do the boring or anything, but the lathe work for the pistons yes.
I also have a few spare old pistons to use for practice.

I this thread and a build thread for the chop

[RAFster122s]

There is a guy on ebay who will do cylinder boring for ~$125. But the sleeves need pressed out after the cylinder is heated, the bored for the larger sleeves, cylinder casting heated, new sleeves pressed in. Doubt he does that but he might. APE can do it but it won't be cheap but it will be done right. I have a Henry Abe 605cc kit where one of the liners dropped. I picked it up for little money in that shape. I want to have the pistons modified to take a three piece or two piece oil ring instead of the stock one piece. Doing either Total seal rings or set of Honda OEM rings...

[01Thomas]

OK, Thanks Scunny

here you go
http://forums.sohc4.net/index.php?topic=20601.0

[RAFster122s]

You don't need his services, he does overbores for that $. So for a Henry Abe or a 60-61 mm overview on a 550 he would be inexpensive.
You can pull the liners yourself  with a oven and mallet after blocking up the cylinders after it comes out of the oven. Saves a little labor $.

There is a guy on ebay who will do cylinder boring for ~$125. But the sleeves need pressed out after the cylinder is heated, the bored for the larger sleeves, cylinder casting heated, new sleeves pressed in. Doubt he does that but he might. APE can do it but it won't be cheap but it will be done right. I have a Henry Abe 605cc kit where one of the liners dropped. I picked it up for little money in that shape. I want to have the pistons modified to take a three piece or two piece oil ring instead of the stock one piece. Doing either Total seal rings or set of Honda OEM rings...

[bwaller]

If this is a 550, the sleeves are thick enough to bore for 61mm pistons

[Tews19]

I am pretty sure you can even use the 61.5mm 120 buck kits on ebay..... I got mine in the mail yesterday for my 550 build... Pistons look great

[jaguar]

Motor is a 550.

Worth it to have the crank bal/lightened?

[Tews19]

Dmitri13 is currently putting his build back together.. He had his lightened by APE.. I asked what the benefits are.. He mentioned less weight, higher revving capabilities....

[seanbarney41]

Motor is a 550.

Worth it to have the crank bal/lightened?

not generally known as a low/mid range torque enhancement

[bwaller]

Balancing the crank is good, send the rods too. I race one and choose not to lighten it. Theoretically it will spin up quicker, but won't make more power or rev higher.

[RAFster122s]

I am pretty sure you can even use the 61.5mm 120 buck kits on ebay..... I got mine in the mail yesterday for my 550 build... Pistons look great

The CB500 was not able to overbore to 61mm, this is why the Henry Abe "605" (actually 592cc) kits had liners. The CB550 is safely able to go to 61mm with very thin liners, 61.5 is do able with extremely thin liners. If I recall correctly, the stock STD bore CB750 piston is 61mm.
I have an uninstalled Henry Abe kit that a PO bought a set of CB550 cylinders and had the liners removed and install the Henry Abe liners. While I can't measure the standard liners I can measure and provide the Henry Abe kit liner diameter. I wonder if it was 750 liners or 550 liners or something else. Now I am curious...

[RAFster122s]

Is not balancing and blueprinting the process of making the pistons and rods equal weight to provide maximum potential and equalizing the loads on the motor. It might be worthwhile to have this done if it is not going to be very e$pensive.

Doesn't lightening your crank affect your torque? Or, am I confusing that with the lightening of the flywheel?
Is the equivalent of the flywheel for a bike the lightening of the stator? If not, why is the stator sometimes lightened?
Does lightening the crank impact your torque, thus as someone (forgot who) alreadyy pointed out it is not going to give you low end power (torque)?
Since torque affects your ability to accelerate this is what you want to increase which the added displacement provides. The Gentleman's Express build does not raise compression to high levels which will, if I recall correctly, raises hp in combo with the displacement boost. High compression will often require you to run higher octane gas to prevent pre-detonation or pinging/pinking which can damage the motor. This is the only reason you would need to run higher than regular gas in the SOHC/4 bikes, as it will not affect fuel economy in a stock motor.

(Edited to add) >
One more thing, the 750 has gobs more torque in part to the displacement. More torque is one thing that makes the CB550 more fun in the twisties and on moderate hills. The high displacement 592cc or Gentleman's Express will create a bike that can spank most any stock 750 handily. Doubt it is going to have a chance against the 836cc 750 though...
Brent has built a monster of a 550 that has done well against some VRRA 750s if I remember well.
< (edit end)

Sorry if I digressed from the thread's topic a bit...I thought it might be good to ask and raise these points within the scope of the OP topic.

[RAFster122s]

Motor is a 550.

Worth it to have the crank bal/lightened?

not generally known as a low/mid range torque enhancement

Balancing can increase torque and hp in a stock displacement motor since the imbalance impacts the motor's ability to run and rev as smoothly and with less effort.

[Tews19]

Thanks for the correction Bwaller and detailed explanation Rafster!

Curious, should I attempt to get me a set of 750 cylinders for my 550 61.5mm pistons? There is a current member who recently completed this build. He said he has no issues yet. I understand the sleeves will be much thinner and to compensate for the added heat I am planning to run an oil cooler...

[jaguar]

I wonder if they are actually cb750 sleeves...

So now I am officially on the hunt for the parts to build this motor.
-"300" 750 pistons.   I found some singles on the bay for $40, guess that is the best deal.
-the correct sleeves.  There is a set of cb500 powroll sleeves, will they work?
-what cam should I run?
-what should I run for a clutch?
-is there something worth doing in the bottom end?  Chain?  650 sump or tensioner?

[jaguar]

Also what head gasket?

[bwaller]

Again with 61mm pistons the stock 550 sleeves are thin but ok. I would be nervous boring them 0.5mm further however because they will be VERY thin. I think Pauages used DOHC CB750 sleeves in his. I don't know about the Powroll sleeves but expect they wouldn't be much different that the 550 sleeves.

A stock clutch is fine but maybe replacing with new plates/discs/springs is wise. I use stock parts in both my wifes 592 and my racebike.

If you don't know their history I would replace both the camchain & primary chain as well, plus crank/rod bearings if they're questionable. They make a difference in maintaining proper oil pressure. All this talk on here about low pressure, here's your chance. I like the CB650 primary chain tensioner. It isn't necessary but likely prolongs the chain life especially in a race engine on "over-run".

I use copper head gaskets but they will always weep some. They can be annealed & reused and o-ringed but are not the best gasket for a street bike. I'm going to replace with an MLS head gasket in the 592. I think with clean surfaces these are the best.

There are good cam choices but if it's a street bike choose a street cam. But be fore-warned if you get a new cam consider replacing with new rockers or get your used ones hardwelded. This process is tough and after three seasons of torture still look new. I have seen many burnt cams from mating with worn rocker pads.

It's only money.