Topic: Something new and interesting for F2/F3 engines!

[HondaMan]

Mark,

You're talking high compression. I myself consider high compression pistons to be 12.5:1. What numbers are you referring to here? Stock are generally 9:1/9.2:1 ; normal bore kits are ~10.5:1 ; normal high compression  are usually 12.5:1.

Perhaps a little confusion without the numbers?

 

The numbers I usually go by are: less than 10:1 is normal compression (with the cast pistons, anyway). Back 'in the day' the vendors like Rocky Cycle, Action Fours, Powroll and the like called anything above 10:1 "high compression". Powroll's original claim to fame was 11:1 pistons that were forged and ran OK (except for oil leaks) on the street with stock rods. I have an 836 engine in my garage (K1) that has these inside. They were not lighter than OEM pistons, though, by a stretch. I inherited the engine after it leaked so badly at 2000 miles that the owner parked it (30 years ago).

[kmb69]

Really interesting discussion about piston/bore experiences!

I can contribute with photos of 2 pistons. Forged and cast
Forged RC836 that only got about 8000kms. Touring to former Jugoslavia took 5000kms.
Destroyed, but skirts look nice with the brick pattern

Cast Action Fours that replaced the RC pistons, hone bores only and in they went.
I think about 28000kms. 3 tourings going south to Austria, Italy twice, Spain once. About 17000 kms touring.

Edit: The Forged RC pistons are slightly slimmer than the cast Action Fours.

I'll soon open the engine again and I'm curious how my NOS RC cast pistons will look after 5000 kms, half with too lean carbs. Same bores honed again and in they went with 3-piece oil rings from my old Action Fours.

Maybe the bore and pistons will look scuffed? New investments

PeWe, Do your Action Fours cast pistons have "ART" in the casting relief on the side? I know early on they were machining Honda CB350 pistons for their 812 and 836 kits.
Those RC pistons appear to be quite a bit higher compression. What is destroyed about them? Do they have "Arias" underneath the crown?

[MRieck]

Really interesting discussion about piston/bore experiences!

I can contribute with photos of 2 pistons. Forged and cast
Forged RC836 that only got about 8000kms. Touring to former Jugoslavia took 5000kms.
Destroyed, but skirts look nice with the brick pattern

Cast Action Fours that replaced the RC pistons, hone bores only and in they went.
I think about 28000kms. 3 tourings going south to Austria, Italy twice, Spain once. About 17000 kms touring.

Edit: The Forged RC pistons are slightly slimmer than the cast Action Fours.

I'll soon open the engine again and I'm curious how my NOS RC cast pistons will look after 5000 kms, half with too lean carbs. Same bores honed again and in they went with 3-piece oil rings from my old Action Fours.

Maybe the bore and pistons will look scuffed? New investments

PeWe, Do your Action Fours cast pistons have "ART" in the casting relief on the side? I know early on they were machining Honda CB350 pistons for their 812 and 836 kits.
Those RC pistons appear to be quite a bit higher compression. What is destroyed about them? Do they have "Arias" underneath the crown?

Those Action Fours look like OEM Honda pistons to me. The other look like Arias. They don't look "destroyed" unless the crowns are screwed up.

[HondaMan]

PeWe's pictures brings up an old question I have always had: it involves the deep "oil grooves" found on some of the forged pistons, like the ones in his pictures (I think RC did these?).

My question results from working with a tuner who taught me how to make 12,000+ RPM engines. He worked mostly with 2-strokers (running them to 10000+ RPM) until I came along one day and asked for his help to build the 750 into a midget-racer car engine (I was helping someone else, it wasn't my project). This long-time (and 60-something years old in 1972) tuner would take his 2-stroke pistons and, among many other things, hand-dimple them about .002" deep all along the front and back skirts, about 2/3 of the way up from the bottom, with his Bridgeport. He then made the bores 0.0004" (that's not a typo) clearance. His 1- and 2-cylinder strokers would run an entire roadrace season (in our little circuit's 0.5 and 1-mile tracks) without wearing out the rings, running easily 10,000 RPM the whole race: his Hodaka and MAC engines would run over 12,000 RPM.

When I asked him about his assistance for a 750, the first thing he did was: used 0.5mm overbore, glass-beaded the pistons (!), then dimpled them like he did the 2-strokers. We trimmed back the shoulders of the pistons 1.0mm and rounded the resulting dome edges, and milled the head 1.5mm before cutting pockets into the pistons to clear the intake valves. Then we shimmed the springs and installed a cam (I have no idea who made the cam in this one), and he bored the engine to 0.0004", like his strokers. He claimed that the oil in the dimples would both cool the engine better (which makes perfect sense) and would prevent it from ever seizing. The engine easily ran over 10,000 and often ran 12,000 in the first 2 gears (4-speed 1/4 midget car), and the owner ran it 2 seasons with nothing more than oil and sparkplug changes. At the end of the 2nd year he tore it down to look, and the inside looked brand-new, no scratches, nicks, and barely even the grey sheen worn off the skirts.

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?

All the literature I have read (for years) on the forged pistons has been directed to water-cooled engines. I have never seen a good tech book or story on using them in air-cooled engines, at least not since a 1958 text I read in 1972, by an Englishman who designed airplane engines (including the 2 types of Merlin engines for the Mustang P51). Those were all directed toward supercharged and turbocharged engines, not lowly carb'd engines like [most of] ours. These air-cooled heads run much higher temps around the piston crowns than do water-cooled engines, so that has much to do with the [unknown, to me] differences, I'm sure.

[Jerry Rxman Griffin aka MuthaF'er]

Could it be the denser forgings retain heat much more?

[kmb69]

.....
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?
.....

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.

[kmb69]

Could it be the denser forgings retain heat much more?

No. They actually dissipate heat faster.

[HondaMan]

.....
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?
.....

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.

Thanks for the article: I shall study on it!

[PeWe]

PeWe, Do your Action Fours cast pistons have "ART" in the casting relief on the side? I know early on they were machining Honda CB350 pistons for their 812 and 836 kits.
Those RC pistons appear to be quite a bit higher compression. What is destroyed about them? Do they have "Arias" underneath the crown?

Those Action Fours look like OEM Honda pistons to me. The other look like Arias. They don't look "destroyed" unless the crowns are screwed up.

kmb69:  Yes, ART inside! Pistons purchased end of 1984.

Mike: The old forged RC look really nice except for the crowns, especially 2 and 3... the upper end of the rods (bluish).
That melt down was not fun that late summer 1984 when I had invested a lot in the bike the winter before.

The crown look rather thin were meleted, maybe 3mm thick...
Back to my tuner that had new pistons and mounted used rods, valves, user guides....Back on the road next summer.

[MRieck]

Skirt clearance is also very dependent on how much taper is machined into a piston. I don't think that point has been mentioned.

[PeWe]

About taper... I'll measure the old pistons again.

[kmb69]

kmb69:  Yes, ART inside! Pistons purchased end of 1984.

Mike: The old forged RC look really nice except for the crowns, especially 2 and 3... the upper end of the rods (bluish).
That melt down was not fun that late summer 1984 when I had invested a lot in the bike the winter before.

The crown look rather thin were meleted, maybe 3mm thick...
Back to my tuner that had new pistons and mounted used rods, valves, user guides....Back on the road next summer.

The lack of wristpin oiler holes in the RC pistons undoubtedly contributed to the overheated pins and rod small ends. Center pistons running a little hot under some conditions. Ignition timing probably needed to be slightly retarded for that setup.

And I should add, you probably needed a little higher octane fuel.

[Justin]

.....
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?
.....

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.

Interesting read on that performance pistons article. Especially the take on coatings as I'm increasingly interested in coating internals when building engines.
Cheers


Sent from my iPhone using Tapatalk

[bwaller]

Good article Keith. Concerning those RC pistons I'll bet they had horizontal slots machined in the pin hole for lubrication instead of the vertical holes in the boss..

[kmb69]

Maybe, Brent. It seems like the RC pistons were overheating from the pin up or crown down. Skirts still look pretty good.

[PeWe]

kmb69:  Yes, ART inside! Pistons purchased end of 1984.

Mike: The old forged RC look really nice except for the crowns, especially 2 and 3... the upper end of the rods (bluish).
That melt down was not fun that late summer 1984 when I had invested a lot in the bike the winter before.

The crown look rather thin were meleted, maybe 3mm thick...
Back to my tuner that had new pistons and mounted used rods, valves, user guides....Back on the road next summer.

The lack of wristpin oiler holes in the RC pistons undoubtedly contributed to the overheated pins and rod small ends. Center pistons running a little hot under some conditions. Ignition timing probably needed to be slightly retarded for that setup.

And I should add, you probably needed a little higher octane fuel.

Yes, melted 2-3 indicate the ignition. I remember that we talked about as advanced as possible when setting the ignition back in those days. Advance until pinging on 5:th gear and almost full throttle at 100-120kmh (4000-5000rpms). I guess I forgot to check the point 2-3, too much turn the plate only.

Octane was highest available gas station fuel. I used Mikuni VM29 that had bad carb boots that cracked very quickly. I was convinced that the leaking carb boots caused the problem. I used OEM carbs after that. Lean due to leak and too advanced ignition... not good combo...
RC pistons had nice compression with really good responce when twistingthe  throttle.

I have not had any thought about the obvious, piston pin have bad oil support!!!  Too late for warranty??
Only one hole that enter under the oil rings.

More photos of piston measurements. RC pistons a little bit smaller to give for more clearance?

Edit: RC rings can be used on the AF pistons, all RC rings fits. I read somewhere that Action Fours 836 used CB350 twin +1mm rings.
 The even older (for me newer) NOS cast RC have same sized rings (came with 1 piece oil ring). Better lubrication/cooling with oil holes!

Yes, I grinded the valve pockets for the 34mm IN valves when photo below show tight fit. At least +1.5mm free around the center punch mark thru the guide when testing the head on.

[HondaMan]

kmb69:  Yes, ART inside! Pistons purchased end of 1984.

Mike: The old forged RC look really nice except for the crowns, especially 2 and 3... the upper end of the rods (bluish).
That melt down was not fun that late summer 1984 when I had invested a lot in the bike the winter before.

The crown look rather thin were meleted, maybe 3mm thick...
Back to my tuner that had new pistons and mounted used rods, valves, user guides....Back on the road next summer.

The lack of wristpin oiler holes in the RC pistons undoubtedly contributed to the overheated pins and rod small ends. Center pistons running a little hot under some conditions. Ignition timing probably needed to be slightly retarded for that setup.

And I should add, you probably needed a little higher octane fuel.

On this topic: I recently did a Wiseco engine in 836, and one of the 4 pistons in the kit had no oiling holes in the wristpin bosses, while the other 3 did. When I contacted Wiseco about this, they said 'go ahead and use it as it is", to which I took exception and made them send me another pistons like the first 3. I debated drilling my own, but there were also slight weight differences between the odd piston and the others that I didn't like. Wiseco was NOT friendly about it, either...I haven't done another Wiseco engine since.

Oh...and also on that kit: one of the 2nd rings for one of the pistons had a defect in it (a void) alongside the inner edges of the ring: I saw it, ignored it, but as soon as I spread the ring to install on the piston, it snapped like a carrot at that site. I had to BUY another set of rings, even after I sent it back for their examination: they claimed it was fine and I over-spread it. Not...

[Swoop]

Well, at least you got a reply. I contacted them with an issue....and they said that I would have a response within 3 days....nothing!
I will never use Wiseco again.

Steve

[kmb69]

The lack of wristpin oiler holes in the RC pistons undoubtedly contributed to the overheated pins and rod small ends. Center pistons running a little hot under some conditions. Ignition timing probably needed to be slightly retarded for that setup.

Yes, melted 2-3 indicate the ignition. I remember that we talked about as advanced as possible when setting the ignition back in those days. Advance until pinging on 5:th gear and almost full throttle at 100-120kmh (4000-5000rpms). I guess I forgot to check the point 2-3, too much turn the plate only.

Octane was highest available gas station fuel. I used Mikuni VM29 that had bad carb boots that cracked very quickly. I was convinced that the leaking carb boots caused the problem. I used OEM carbs after that. Lean due to leak and too advanced ignition... not good combo...
RC pistons had nice compression with really good responce when twistingthe  throttle.

I have not had any thought about the obvious, piston pin have bad oil support!!!  Too late for warranty??
Only one hole that enter under the oil rings.

More photos of piston measurements. RC pistons a little bit smaller to give for more clearance?

Edit: RC rings can be used on the AF pistons, all RC rings fits. I read somewhere that Action Fours 836 used CB350 twin +1mm rings.
 The even older (for me newer) NOS cast RC have same sized rings (came with 1 piece oil ring). Better lubrication/cooling with oil holes!

Yes, I grinded the valve pockets for the 34mm IN valves when photo below show tight fit. At least +1.5mm free around the center punch mark thru the guide when testing the head on.

I see. Thanks for the additional pictures. They were trying to "force" feed the pins. After hearing the rest of the story, it is doubtful the excessive heat was from the pins. Sounds like you had several reasons for the crowns to overheat.

[MRieck]

The lack of wristpin oiler holes in the RC pistons undoubtedly contributed to the overheated pins and rod small ends. Center pistons running a little hot under some conditions. Ignition timing probably needed to be slightly retarded for that setup.

Yes, melted 2-3 indicate the ignition. I remember that we talked about as advanced as possible when setting the ignition back in those days. Advance until pinging on 5:th gear and almost full throttle at 100-120kmh (4000-5000rpms). I guess I forgot to check the point 2-3, too much turn the plate only.

Octane was highest available gas station fuel. I used Mikuni VM29 that had bad carb boots that cracked very quickly. I was convinced that the leaking carb boots caused the problem. I used OEM carbs after that. Lean due to leak and too advanced ignition... not good combo...
RC pistons had nice compression with really good responce when twistingthe  throttle.

I have not had any thought about the obvious, piston pin have bad oil support!!!  Too late for warranty??
Only one hole that enter under the oil rings.

More photos of piston measurements. RC pistons a little bit smaller to give for more clearance?

Edit: RC rings can be used on the AF pistons, all RC rings fits. I read somewhere that Action Fours 836 used CB350 twin +1mm rings.
 The even older (for me newer) NOS cast RC have same sized rings (came with 1 piece oil ring). Better lubrication/cooling with oil holes!

Yes, I grinded the valve pockets for the 34mm IN valves when photo below show tight fit. At least +1.5mm free around the center punch mark thru the guide when testing the head on.

I see. Thanks for the additional pictures. They were trying to "force" feed the pins. After hearing the rest of the story, it is doubtful the excessive heat was from the pins. Sounds like you had several reasons for the crowns to overheat.

Agree 100%. Pin bores still look clean (can still see the hone marks).

[HondaMan]

Well, at least you got a reply. I contacted them with an issue....and they said that I would have a response within 3 days....nothing!
I will never use Wiseco again.

Steve

Yeah, I got that response twice: after another week I called them 3 times in one day until I got someone who would answer their phone. That was enough for me....

[MRieck]

kmb69:  Yes, ART inside! Pistons purchased end of 1984.

Mike: The old forged RC look really nice except for the crowns, especially 2 and 3... the upper end of the rods (bluish).
That melt down was not fun that late summer 1984 when I had invested a lot in the bike the winter before.

The crown look rather thin were meleted, maybe 3mm thick...
Back to my tuner that had new pistons and mounted used rods, valves, user guides....Back on the road next summer.

The lack of wristpin oiler holes in the RC pistons undoubtedly contributed to the overheated pins and rod small ends. Center pistons running a little hot under some conditions. Ignition timing probably needed to be slightly retarded for that setup.

And I should add, you probably needed a little higher octane fuel.

On this topic: I recently did a Wiseco engine in 836, and one of the 4 pistons in the kit had no oiling holes in the wristpin bosses, while the other 3 did. When I contacted Wiseco about this, they said 'go ahead and use it as it is", to which I took exception and made them send me another pistons like the first 3. I debated drilling my own, but there were also slight weight differences between the odd piston and the others that I didn't like. Wiseco was NOT friendly about it, either...I haven't done another Wiseco engine since.

Oh...and also on that kit: one of the 2nd rings for one of the pistons had a defect in it (a void) alongside the inner edges of the ring: I saw it, ignored it, but as soon as I spread the ring to install on the piston, it snapped like a carrot at that site. I had to BUY another set of rings, even after I sent it back for their examination: they claimed it was fine and I over-spread it. Not...

Mark....I think the lack of oil holes through the bottom of the pin bosses is fine. In fact Smokey Yunick said it ( the type of set up used with the Wiseco pistons you described) was the best method to supply lubrication to the pin bore. This is on page 51 of "Power Secrets". I think Smokey had forgotten more than all of us combined will ever know about 4 stroke engines.

[HondaMan]

kmb69:  Yes, ART inside! Pistons purchased end of 1984.

Mike: The old forged RC look really nice except for the crowns, especially 2 and 3... the upper end of the rods (bluish).
That melt down was not fun that late summer 1984 when I had invested a lot in the bike the winter before.

The crown look rather thin were meleted, maybe 3mm thick...
Back to my tuner that had new pistons and mounted used rods, valves, user guides....Back on the road next summer.

The lack of wristpin oiler holes in the RC pistons undoubtedly contributed to the overheated pins and rod small ends. Center pistons running a little hot under some conditions. Ignition timing probably needed to be slightly retarded for that setup.

And I should add, you probably needed a little higher octane fuel.

On this topic: I recently did a Wiseco engine in 836, and one of the 4 pistons in the kit had no oiling holes in the wristpin bosses, while the other 3 did. When I contacted Wiseco about this, they said 'go ahead and use it as it is", to which I took exception and made them send me another pistons like the first 3. I debated drilling my own, but there were also slight weight differences between the odd piston and the others that I didn't like. Wiseco was NOT friendly about it, either...I haven't done another Wiseco engine since.

Oh...and also on that kit: one of the 2nd rings for one of the pistons had a defect in it (a void) alongside the inner edges of the ring: I saw it, ignored it, but as soon as I spread the ring to install on the piston, it snapped like a carrot at that site. I had to BUY another set of rings, even after I sent it back for their examination: they claimed it was fine and I over-spread it. Not...

Mark....I think the lack of oil holes through the bottom of the pin bosses is fine. In fact Smokey Yunick said it ( the type of set up used with the Wiseco pistons you described) was the best method to supply lubrication to the pin bore. This is on page 51 of "Power Secrets". I think Smokey had forgotten more than all of us combined will ever know about 4 stroke engines.

No doubt you're right about Smokey! He was brilliant. He was the god of the midget-car guys I used to work with in the 1970s: they used his book(s) to settle their arguments during the off season 'racing discussions' (usually involved beer...).

I have noticed, for instance, that my Ford (car) engines don't have them, but the Toyotas I've rebuilt did (and the Honda and Suzuki bikes, too). Maybe it's a Japanese thing? But I should also say that I noticed the Ford pins to be seized in their pistons, pretty much, making them a bugger to disassemble. I had to press them out of their rods (on every Ford engine I have rebuilt). Then the new ones were a slip-in fit. So, I suppose the Japanese approach is to let them be lubed so the engines are easier to work on, maybe? They certainly don't claim to get automotive-like miles from these engines, so I tend lean in this 'service-ability' direction about them.

And now I wonder: why would having them un-lubed in the pistons be an advantage?

[bwaller]

Mark, I believe Mike is alluding to the fact that Wiseco prefers to machine horizontal recesses in the pin boss for lubrication.

[HondaMan]

Mark, I believe Mike is alluding to the fact that Wiseco prefers to machine horizontal recesses in the pin boss for lubrication.

That sort of confuses me, then? The one piston in the last Wiesco kit I got that was odd had no holes at all. Nor do my Fords, the 3 that I have that I also rebuilt. But now, I am curious as to why some designs would have them while others don't? Seems like a good winter research project.