Topic: Gentleman's Express 550 engine build

[HondaMan]

Can we stop the pissing match over forged pistons. Yes newer forgings are way better than the old.  HondaMan chooses not to use them from past experience and i don't think anyone could blame him for choosing what he knows works and is reliable on a build for someone else. You guys have already shared you thoughts and information so lets move on and get back to the point of this thread.

It was a legitimate question about why is choosing to machine a 750 piston versus a modern 59mm piston, forged or cast; they're both available. Im curious about his preference for machining, does it yield different results? I already knew his predilection for cast vs forged, and mentioned that.

So, in summary, Mark, you're choice of a 750 cast versus a new 59 cast (CruzinImage) is what/why? Is there another inherent benefit to the results of your machining the 750 piston that a new 59mm won't yield?

Well, the intent of this build is to bring forward a successful mod of the CB500 from many moons ago, specifically the "Gentleman's Express" build of 590cc in a 500 engine. At the beginning of this project, it was just to be a rebuild with 0.5mm overbore (anyone need a set of .5mm 500 pistons and rings?), but given that little of the original bike will remain (due to its condition) the owner opted to 'go for it' and see how it works out as a very fancy cafe' build. The "Express" has been done many times, so I thought it fun to revisit the 1970s with 1970s hardware and do it again. It had a rep as a "750 killer" back in the day, but I didn't get to see one in action.

I also thought it might encourage others here to make use of the plethora of stock-size CB750 pistons that we all remove every year? Granted, the CruisinImage pistons may already have things like clearanced piston skirts (or shorter ones?), but then, where would the adventurous hotrodder be if everyone made all his parts for him?

[HondaMan]

Gotcha. Missed that "scope and intent" earlier. Seems a noble undertaking and chocked full of good info. Hope my other query didn't derail this too far or cause a misunderstanding.

Not at all: it seems we gotta discuss it somewhere? I have no doubt that guys like MRieck, Bill Benton, and a host of others here can build mighty engines with forged pistons, but that's not where I ended up going, once I quit the racing stuff. I guess it's 'cuz I don't have the $$!

[Retro Rocket]

Can we stop the pissing match over forged pistons. Yes newer forgings are way better than the old.  HondaMan chooses not to use them from past experience and i don't think anyone could blame him for choosing what he knows works and is reliable on a build for someone else. You guys have already shared you thoughts and information so lets move on and get back to the point of this thread.

I'm sure Mark is quite capable of speaking for himself mate, seeings though a lot of members hang on his every word, it thought it would be nice for him to acknowledge that things have indeed changed and his experiences were in the past with inferior pistons, some people would read the comments here and never use something that is perfectly good to use, especially in a performance build. Seeing Marks penchant for sharing very good information {i just bought his book by the way}, I think that it should rate a mention, it was NEVER about a "pissing match", just adding more relevant information for everyone....

[Camrector]

While I do agree that technology has come a very long way, what hasn't changed is the 40 year old engines we are adding these new parts to. Also it seems that the rings are the weak point not the Pistons themselves.
Besides the power increase from the bore/port/cam, reliability was very important. Mark has built many engines that have exceeded 50,000k without having to be rebuilt. I havent heard anyone chime in with a 592 with over 10-15k miles with these newer Pistons. Plus modifying your Pistons is a lot cooler than buying a "kit".
Again though the purpose of this build was a homage to the ingenuity of the past and to focus on real everyday performance and maintain reliability.

[MRieck]

 To bad it took the fella's in the original article 3 times to get a round bore.
  I don't believe the Yosh rings were to blame .......1 quart of oil in 200 miles is more than ring seating and Yoshimura used the same piston and ring manufactures as the bike companies.
Sounds like a very bad boring job (common theme in that original article).

[seanbarney41]

Why would it be hard to ride 50,000 miles in 3 years on a 550?  I did it on a 750 and it was not hard.  It was fun.  A 550 might even be funner.

[SOHC4 Cafe Racer Fan]

Why would it be hard to ride 50,000 miles in 3 years on a 550?  I did it on a 750 and it was not hard.  It was fun.  A 550 might even be funner.

Or even more fun!    Sorry, FTFY. 

[Camrector]

10-15k miles Cal!   

[seanbarney41]

Why would it be hard to ride 50,000 miles in 3 years on a 550?  I did it on a 750 and it was not hard.  It was fun.  A 550 might even be funner.

Or even more fun!    Sorry, FTFY. 

or even funnerer...ftfy

[GV1390]

Why would it be hard to ride 50,000 miles in 3 years on a 550?  I did it on a 750 and it was not hard.  It was fun.  A 550 might even be funner.

Agreed.

I'm coming up on 24k on two motorcycles from April-ish until now (we also have vicious winters where we cannot ride), granted my X-C trip included but still a crap ton of miles.

I'd measure how many go on my 550 once completed but, gauges are for sissies.

[Camrector]

I believe you misunderstood me Cal.
What I said was that Mark has built many engines that have exceeded 50000 miles without needing to be rebuilt using his Pistons of choice.

What I haven't heard was anyone with a 592 and 10-15k miles on it speak to the reliability of the newer Pistons . 2 seperate statements
No math needed

[FunJimmy]

I've even contact the good folks at Rev'it to begin pre-production on touring pants with provisions for adult diapers. I'll be damned if I'll piss myself and interrupt a good ride.

Ditch the diaper Cal. For piss and giggles get yourself a Possitve Flow racing catheter instead. Condom comfort and no need to stop. Should have that 17K dialed in in no time.

http://www.ruggedradios.com/index.php?main_page=product_info&products_id=1352

[GV1390]

I'm coming up on 24k on two motorcycles from April-ish until now (we also have vicious winters where we cannot ride), granted my X-C trip included but still a crap ton of miles.

If memory serves, that X-country trip was on a DOHC 750, no? Not an SOHC 550. I thought you sold that after putting 6k on it? Didn't I read that in another post somewhere? And the newest member of your stable is another late 70's 750K, right? Not sure what your post was proving?

Was referring to putting miles on 2-wheels, period. Don't be so uptight Cal, go enjoy a nice glass of bourbon or something.

[GV1390]

Off topic but, since I had to answer to others I will mention this here to clear up a little confusion.

When I referenced above, I was strictly saying how I, in 10-months worth of riding + a 5k cross-country moto trip to date have put on 23-24k miles. Most of them were done on a 91' Nighthawk 750 that is a DOHC and the others were on my "new" daily which is an 04' SV650.

Whomever would like to dicsuss in further, please pm ME.

[HondaMan]

Hey Mark - Back to your piston mods, do you have an idea of the weight difference between the altered 750 and the stock 500 piston? I'm curious as to the effect that a "seemingly" heavier, larger piston would have on the rotating mass. How do you deal with this offset against the crank and trans? Or is it so negligible as not to effect it, but simply rebalance with the rods in place?

I'll go find my wife's digital 'dough' scale and measure them? I'm sure they are heavier, don't know yet by how much, though. Her scale may not be absolute-accurate, but it will at least show the grams difference between 2 pistons.

[Restoration Fan]

I've even contact the good folks at Rev'it to begin pre-production on touring pants with provisions for adult diapers. I'll be damned if I'll piss myself and interrupt a good ride.

I'm really tempted to sig this so that it shows up in the bottom of every one of my posts!

[HondaMan]

I'll go find my wife's digital 'dough' scale and measure them? I'm sure they are heavier, don't know yet by how much, though. Her scale may not be absolute-accurate, but it will at least show the grams difference between 2 pistons.

So is there no modifications needed "generally" when you do use the 750 pistons? (Talking about to the rods and crank or trans?)

I haven't found her scale yet, but...the bottoms of the pistons contact the crank weights on 2 of the cylinders. Usually there needs to be 1.5-2.0mm minimum clearance here, so I may have to have the crank weights shaved a bit. The contact is coming from the uneven casting surface of the weights (it's the mold's seam joint ridge for the weights), so if my lathe were big enough, this could be done with a file on a lathe. But, my lathe only swings 7" and the weights are bigger that that, I think. Either way, I'll find out pretty soon?

[bwaller]

Mark, in the original GE article they cut the 750 piston skirts some to manage that crank clearance issue. It's good to balance a crank and would have to be done if you remove material from only some of the cranks weights. Why not just machine all the pistons similarly and reduce their weight some?

Another little ditty, I have found by checking modified piston/head clearances with clay & solder that the piston dome angle should be 13 degrees. The chamber is 15d so this slight piston angle change works positively if squish clearances are tight enough.

[HondaMan]

Okay. But I still haven't explained my question I guess. Typically with this type of modification, if the piston is heavier by a considerable amount, doesn't it create more stress on the rods and thereby crank/transmission timing and slow the rate of crank acceleration? After all, you're pushing a heavier piston now (thats why I was curious to the weight delta between the 550 and 750) and has this modification historically not required mods also the lower end?

Im asking, not asserting, since you have history with this modification and parts choice.

According to all the 'soothsayers', this answer was traditionally, "Yes". They claimed that adding piston weight required rebalance of the cranks, maybe heavier rods, etc. In practice, though, we've seen that Honda was so concerned about possibly 'losing face' over these early Fours that they overbuilt the bejeebers out of these engines: we can run 10:1 CR 836cc cast pistons in the 750, for example, that are 5% heavier than the OEM pistons, to 10k RPM with no grief (except oil leaks, if the studs are not HD type!). This was the same situation as was found in the older CB/CL Twins, where you could sling the biggest pistons you could keep inside a sleeve, and they never seemed to do more than maybe vibrate a bit. Well, more than a bit: my SuperHawk thus modified did crack half of its license plate off during a tour to Missouri one summer, got home with just "H-..." left on my plate!

When you look at the overall quality of the smaller Fours (inside the engines), it is surprising how poor the castings are compared to the 750 series. I think this may be why they were so de-tuned in their performance (35-38 HP on the 500) relative to the 750, so the parts were not stressed much. The crank and rod bearings, even the piston pins, in this particular engine are gigantic when compared to their contemporary Suzy or Kawi counterparts, so even those who decided to add blowers to the 500/550 bikes didn't have to add much to their bottom ends. In the end with this one, I think the bike will lose its silky-smooth 500 nature a little bit, but not so much as to be uncomfortable.

In this case, if I were planning on racing the bike, I'd be doing some things differently, for sure. For one, I'd be using the shorter 61mm pistons, probably go to the trouble of finding the tightest crank bearings I could (not much available for these right now, but the normal clearances will be fine for street) and shot-peen the rods, using ID tapered wristpins, and all that fancy stuff. And to be sure, if one were being built for that sort of thing, that's what should happen!

[HondaMan]

Mark, in the original GE article they cut the 750 piston skirts some to manage that crank clearance issue. It's good to balance a crank and would have to be done if you remove material from only some of the cranks weights. Why not just machine all the pistons similarly and reduce their weight some?

Another little ditty, I have found by checking modified piston/head clearances with clay & solder that the piston dome angle should be 13 degrees. The chamber is 15d so this slight piston angle change works positively if squish clearances are tight enough.

Thanks for the dome angle, "B"! That helps. I just bought a new angle gage to try to figure it out. The quench bands on the head are now opened 3mm, but they are still straight-across (flat) from the bore to the chamber. The pistons are about 1.2mm too tall for that, so they do need to be trimmed. I've been doing this with the DOHC pistons on the post-1975 SOHC engine rebuilds, cutting off 1.5mm of height to clear the quench area, but those are only a bore difference of +1.0mm. This one is much bigger!

There isn't enough skirt below the rib (inside the skirt) to allow cutting enough to get a full 1.5mm clearance, and I am a little squeamish about running with less clearance than that. On Ford and H-D engines, much modified, their rule was always .060" (1.5mm) minimum clearance - although, on the H-D engines this always made the rear cylinders burn oil because it put so much crankcase pressure on its oil ring, due to the off timing those have. At least these engines are more balanced than that!


The crank weights have some sloppy casting joint ridges that are causing the clearance issue. It's not the full circumference of the weights, it's just where those seams are from the molds, and only on #1 and #4. I am going to take the assembly to my racer shop here to discuss the trim, and see if they will post-balance it for a reasonable cost. Otherwise, I'll likely just trim it, if they want too much $$. We're only talking a couple of grams, here....

[scottly]

With a flat-plane, fully counter-weighted crankshaft, the crank does not need to be re-balanced for heavier or lighter pistons or rods. All four pistons should weigh the same, and all four rods; both the small ends, big ends, and total rod weight should be the same. If you remove material from the crank to clear the piston skirts, then the crank will need to be re-balanced, but that alone would put the GE upgrade out of the budget modification class. Modify the pistons to fit the crank, not the other way around.

[redwillis1978]

 Could you machine the case halves and convert to roller bearings? Get rid of the ABBA bearing halves.

[Tintop]

Could you machine the case halves and convert to roller bearings? Get rid of the ABBA bearing halves.

Likely doable......however, would require a new custom 'built-up' crank, along with all the specialized machining.  big,big $'s required!   The cost would make an APE crank with Carrillo's look very inexpensive.

[HondaMan]

Could you machine the case halves and convert to roller bearings? Get rid of the ABBA bearing halves.

Not in these engines with the hi-pressure oil pump systems, at least not without modifying the way oil is metered to those bearings (like adding oil metering jets to each bearing). Roller bearings use pressures around 5-9 PSI, because they have no restriction: instead of high pressure, engines like that have high-flow pumps. Similar examples within the Honda family are: anything made before the CB750. The early bikes all had low-pressure, hi-flow systems with roller-bearing cranks. Kawi went the roller-bearing route on their Fours of the era, too, and their oil PSI is around 7 when hot. The cranks don't last all that long, either: typical Z1 or KZ1000 crank life seems to be less than 30k miles, where these SOHC4 bottoms ends can easily go 100k miles or more (mine went 138k+ and still worked fine, and Ofreen's is well over 150k).

[RAFster122s]

I've even contact the good folks at Rev'it to begin pre-production on touring pants with provisions for adult diapers. I'll be damned if I'll piss myself and interrupt a good ride.

Ditch the diaper Cal. For piss and giggles get yourself a Possitve Flow racing catheter instead. Condom comfort and no need to stop. Should have that 17K dialed in in no time.

http://www.ruggedradios.com/index.php?main_page=product_info&products_id=1352

Jimmy, do they make one that provides injection of said catheter into the exhaust so it is vaporized, perfect thing for the track to have your trailing opponents have to smell your burning...well...
Might be like an afterburner if you alcohol consumption were to make it to your bladder.   Just need a flame arrestor so it couldn't back up the tube to your nether regions...