Topic: Gentleman's Express 550 engine build

[Retro Rocket]

Hey Mark- Perhaps in an effort to re-track this thread away from clutch options, you could elaborate your preference for modifying a cast 750 piston versus purchasing a new forged unit? I know from other posts, you appear to be gun shy over forged units, but with all the guys running them, it seems these issues are no longer prevalent.

This was well and truly covered in the other thread you mention Cal. Modern forged pistons are far superior to the old ones Mark has had his experiences with, I'm not sure why he fails to mention that here, there were some very detailed posts in that other thread....
for example:

Quote from: HondaMan on December 08, 2015, 07:42:49 PM

    .....
    So, here's the question I've had ever since: why do the forged pistons require so much clearance, and when not given the clearance (as in my old SuperHawk, when I didn't give it .0022" the first time), the pistons WILL stick? And, even when the forged pistons have been micro-grooved around their entire circumference to hold oil, they still need this extra clearance? Do they really grow 4x as much as cast pistons?
    .....
KMB69

It depends on the alloy used in the casting or forging as well as the machining practice as Mike mentioned earlier. They do not grow 4x as much as cast pistons. The aluminum alloys pretty much range in their Coefficient of Expansion from a low - Cast Alum 201.0-T4 (95HB) at 12.8 µin/in-°F to a high - Wrought Alum 5652-H38 (50HB) 13.2 µin/in-°F. The % of silicon used in the piston alloy, whether they are hypereutectic, eutectic, or hypoeutectic effects their Coefficient of Expansion. You keep referring back to "old" tech pistons which by today's standards are/were pretty much junk. Piston alloys whether cast or forged have come a long way in just the last 10 years. It's not just aluminum either - many alloys are dramatically improved. Have you seen the stock rods out of a Honda CB1300S Super Bol D'or? They are about half as thick as a 1983 CB1100F's rods and they are slinging 78mm pistons. Attached is an article, "Performance Pistons", from Engine Builder Magazine that may provide a better understanding.

Post 30 has the PDF file mentioned in the above post..

http://forums.sohc4.net/index.php/topic,153499.msg1757968.html#msg1757968

[hsas.69]

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.

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[calj737]

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?

[hsas.69]

That i am curious about myself calj. I'm planning a very similar build to this for my 78.

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[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?

[calj737]

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.

[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).

[calj737]

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.

Easy, Big Fella, pretty hard to ride 50,000 miles in 3 years on a CB550. You're asking for a comparison of endurance with 2 inequivalent variables. Sometimes, the cylinder metallurgy actually doesn't matter a lick when new, modern metals and alloys are concerned.

There are ample bikes out there rebuilt with forged pistons doing everything that you aim to do. Now, that is not to take anything away from a "Vintage Mash-up" performance build. Just posted as a ballast. The project looks cool, and if Mark signs him name to it, then you should be quite happy with the outcome.

[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.

[calj737]

10-15k miles Cal!   

Thanks, Math Wiz. Except, thats only 30-45k. More like 17k annually, right?

Its not that "easy" in terms of the average US driver operated their primary vehicle 12-15k niles annually. If you have the climate to rider nearly year round, and the 550 is your primary vehicle, then sure, its bound to occur. If its a secondary vehicle, then you need the freedom and luxury of time to actually ride regularly and signficant distances. Again, lots don't have this luxury. So, time, climate and freedom and then any amount of mileage gets ticked away easily.

This situation is not "most" riders. I love the 5xx platform. Its quick, agile, and a blast ride. Some might even describe it as "more funner" than a 750. Yet, more people tend larger displacement bikes for long rides due to size, power, etc. I know theres heaps of folks who ride 5xxs daily worldwide. Its just not the prevalent choice.

I for one, have put hundreds of thousands of miles on bikes. I'll ride until I am physically no longer able to do so. 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.

[calj737]

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?

[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

[calj737]

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?

[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.

[calj737]

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.

No worries, Jim. The wife have a long time to go before that ever becomes an issue  We will spend our "Golden Years" on two wheels together (2 bikes) traveling this beautiful country of ours. Might even pop up your way for a cold one. Or hot one depending upon the time of year-

[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.