Topic: Gentleman's Express 550 engine build

[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!

[calj737]

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?)

[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?

[calj737]

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.

[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...

[RAFster122s]

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.

There's a certain fellow who did the 750 top end for big bore cylinders I would imagine it would be a lot of CAD work to design a set of cases...and would they be billet or sandcast?     Or castings?

[HondaMan]

OK...those of you suffering from global warming...would you PLEASE send a little of it here, so I can work in the garage again?
 

[HondaMan]

OK, got back into the garage a little today!
 
First thing: modify the pistons (or, get them ready for the machine shop to modify) on the crowns. I made a paperdoll of the 500 piston crown, then traced that to the tops of the 750 pistons. It needs to be cut down 1.2mm (I'll probably go 1.5mm) to match the 500 height. The height is determined by inserting one piston pin into both types of pistons, and measuring the height difference to the 750 crown. Then I scribed it all around for the machine shop guys to cut it back for me.

[HondaMan]

Here's the heigh measurement pix...

[HondaMan]

Oh - and I weighed the 2 different pistons: the 500 piston weighs 4.5 oz., the 750 piston 6.1 oz. on my wife's bread-making scale.
 

[HondaMan]

I'm still trying to worry away the crank weights from the bottoms of the pistons, but I'm getting weightlifter arms from trying(!). My right arm hurts, too, from using someone's [short] tactical shotgun at a skeet-shooting contest 2 days ago - dang gun stock is so short that it ends up clobbering my arm instead of letting it be shouldered while sighting the bird!

I may have to take the crank to the shop for skimming these weights? So far I have only gained 0.5mm on the #3 piston bottom, which is the worst one in this bunch. The crank weights are all over the place with their shapes, which makes it tough!

 

[HondaMan]

Last step for tonight: the primary shaft is really stuck in this engine! It's probably rusty inside, like all the other parts have been, from sitting with wetted oil for 35+ years. I can't get the crank out! Gotta go make a puller, I guess?

[754]

Why not cut that 1.2 mm off the pistons in your lathe  ? Fairly easy to make a fixture.

[Stev-o]

Mark - will the stock 550 rods be used?

Thanks for posting this thread, there are many of us interested in doing this, ncludong me.
Already have a 650 cam on the shelf!

[Trad]

Glad to see you're back in action on this one! Happy New Year!

[scottly]

I'm still trying to worry away the crank weights from the bottoms of the pistons, but I'm getting weightlifter arms from trying(!).

I may have to take the crank to the shop for skimming these weights? So far I have only gained 0.5mm on the #3 piston bottom, which is the worst one in this bunch. The crank weights are all over the place with their shapes, which makes it tough!

 

Well, you're going to have to take the crank to the shop for re-balancing anyway, so you might as well have them do the heavy cutting and save the wear and tear on your body.

[HondaMan]

OK, I got a little collar and a 12x55x1.25mm thread bolt at Ace and made an adapter to fit my genuine Harbor Freight (free to me!) dent puller. Then I threaded it into the primary shaft and [gently] tapped it out. The oil in the spline inside the primary drive clutch assembly was "wet" and it slightly rusted those splines inside there, made it stick a little bit. Got all the other parts stripped from the bottom case to go into the other [bottom] case, still have to do the upper case, dowels, drains, caps, plugs...bearings.

The new crankcase has all "B" size crank holes where the old one was all "A" size, might or might not be a show stopper for parts, will check tomorrow. Sometimes the ID of the cases were borderline and if that's the situation, will install the "old" ones in the "new" crankcases, because they only have 2000 miles on them(!). It all depends on the crank journal actual sizes, will see tomorrow.

[HondaMan]

I also went ahead and clearanced the crank weights (huff, puff...) for all the pistons. The tightest one is #3, with just 1mm between the top of the flyweight and the reinforcement rib of the piston. Since this engine won't be compressing the rods with nitro and 12000 RPM runs all the time, I think that will be enough. I'll check with Axle and the other engine builders around here to see what they like for their minimum, but most of those guys are building engines with 3" and 4" pistons (V-Twins, etc.). Honda has like 5mm in the stock engines, so they didn't have to worry about it...