Topic: 392 Piston rings

[Pbeattie89]

I am looking to get a set 392 piston rings for my 78 cb750k, but I am having a hard time finding a set. I hesitate to use a generic set from 4into1. I was hoping to find a set of riken or OEM rings. Does anyone know where I could get a set?

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[denward17]

What year and size bike?

Your local Honda dealer may have them?

[Pbeattie89]

What year and size bike?

Your local Honda dealer may have them?

It's a 78 cb750k. I added the information to the original post. The dealer does have them, but it would be $400 for 4 ring sets, which is a bit steep for the project.

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[denward17]

South Sound Honda may have them, you could call/send an email and ask:

https://www.southsoundhonda.com/--xpartsstream#/Honda_Powersports/CB750KA_(78)_750_FOUR_K%2c_JPN%2c_VIN%23_CB750-2800001/CRANKSHAFT_%2b_PISTON/14cf52cd-d282-42e1-9a4b-99870811a8c4/5c6c78e0-b4fb-4520-a3fe-69cdd69a061a/y

[Nurse Julie]

Cruzinimage sell the rings and they are made by Riken.

[Pbeattie89]

Cruzinimage sell the rings and they are made by Riken.

I didn't know that. That makes for an easy decision.

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[Pbeattie89]

Cruzinimage sell the rings and they are made by Riken.

I didn't know that. That makes for an easy decision.

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I just emailed crusinimage, and their ring pack are made in Taiwan by an unbranded company. They couldn't confirm the material used ether. They must have changed manufacturers. However, vintagecb750 got back to me, and their rings are made by RIK.

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[PeWe]

My CB750 K2 got Cruzinimage 392 +0.50mm piston set.
Work fine, need tight clearance. I think it got max 0.02mm total.

[Nurse Julie]

Cruzinimage sell the rings and they are made by Riken.

I didn't know that. That makes for an easy decision.

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I just emailed crusinimage, and their ring pack are made in Taiwan by an unbranded company. They couldn't confirm the material used ether. They must have changed manufacturers. However, vintagecb750 got back to me, and their rings are made by RIK.

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Thats strange as the rings in their piston / ring kits are definitely made by Riken 🤔🤔🤔. We've used about 150, maybe more of the Cruzinimage piston/ ring kits on Honda CB SOHC 4's and never had an issue.

[Pbeattie89]

Cruzinimage sell the rings and they are made by Riken.

I didn't know that. That makes for an easy decision.

Sent from my SM-G991W using Tapatalk

I just emailed crusinimage, and their ring pack are made in Taiwan by an unbranded company. They couldn't confirm the material used ether. They must have changed manufacturers. However, vintagecb750 got back to me, and their rings are made by RIK.

Sent from my SM-G991W using Tapatalk

Thats strange as the rings in their piston / ring kits are definitely made by Riken . We've used about 150, maybe more of the Cruzinimage piston/ ring kits on Honda CB SOHC 4's and never had an issue.

It does seem strange, but that's what was said.

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[PeWe]

If rings are worn, bores must be worn too.
As written in other threads, worn rings and oval bores will seal. New rings in worn bores will not.

New pistons will do better.
Cruzinimage has +0.50mm and + 1.0mm piston kits for not much.
A fresh bore for tight piston-bore clearance.
A good shop that can do the job correct, not too sloppy bore.

Clearance ok for forged pistons (0.05mm) will smoke with CI cast pistons.

[Pbeattie89]

If rings are worn, bores must be worn too.
As written in other threads, worn rings and oval bores will seal. New rings in worn bores will not.

New pistons will do better.
Cruzinimage has +0.50mm and + 1.0mm piston kits for not much.
A fresh bore for tight piston-bore clearance.
A good shop that can do the job correct, not too sloppy bore.

Clearance ok for forged pistons (0.05mm) will smoke with CI cast pistons.

I completely agree, but my bores are well within spec, and I have a good set of stock pistons. I am just going to give it a touch-up with a flex hone and a fresh set of rings. If I end up keeping it for any length of time, I am sure I'll end up with an 836cc kit eventually.
My current goal is to get it up and running for this season.

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[HondaMan]

From experience, I might suggest this: the only rings I ever got to actually seal in a stock-bore re-ring job in the CB750 (or the CB350 twins) were the ones WITHOUT the chrome top ring. The stock-size rings in the CruisinImage stock-size piston sets are simple cast iron, which would be similar (as are the ones in their 836cc kits). The rings from MC and RIK have chrome top rings, and a light bore hone job will not seat those (nor Honda's own, for that matter). In other words, you need 'cheap' rings of simple iron material (not hard chrome) for such an 'overhaul', and it won't give you 100% performance, nor last much more than about 10k miles tops.

[xhevi]

Not to highjack this thread but I also trying to decide what rings to get

It's a 76 cb750 stock with 300 pistons and head. With just shy of 10000 miles on it.

With a bore dial gauge i measure between 0.0005 in to 0.001 inch difference in any sleeve in any direction. Gauge zeroed at 2.401in with a micrometer. Also checked the accuracy of both with few feeler gauges.

The rings stuck on the two pistons and I can't get those out. So I was looking at two options:
1) Standard RIK rings from Yamiya plus used set of pistons from eBay
2) standard cruising image kit of pistons with rings. Not fan of this option just because they are aftermarket and read on here that some folks have had issues with rings not sealing well.

Per Hondaman last post sounds like I have another option.

3) non chrome rings (cruising image?) with used eBay pistons? Would this be best choice?

Thanks

[HondaMan]

Not to highjack this thread but I also trying to decide what rings to get

It's a 76 cb750 stock with 300 pistons and head. With just shy of 10000 miles on it.

With a bore dial gauge i measure between 0.0005 in to 0.001 inch difference in any sleeve in any direction. Gauge zeroed at 2.401in with a micrometer. Also checked the accuracy of both with few feeler gauges.

The rings stuck on the two pistons and I can't get those out. So I was looking at two options:
1) Standard RIK rings from Yamiya plus used set of pistons from eBay
2) standard cruising image kit of pistons with rings. Not fan of this option just because they are aftermarket and read on here that some folks have had issues with rings not sealing well.

Per Hondaman last post sounds like I have another option.

3) non chrome rings (cruising image?) with used eBay pistons? Would this be best choice?

Thanks

Your old pistons are the only ones that will now work at all in those bores, as the bores wore to both match those pistons, and the #1 and #4 bores are now egg-shaped (as shown in my book) from the uneven cooling of the SOHC4 engine while it cured. This is specifically why boring them a step-size now makes them last a very, very, very long time without wearing out the rings or pistons: they stay perfectly round forever once the iron liners have cured. Just one example: mine went from 50k miles to 126k miles with the 1st oversize pistons and rings, and at that teardown (for a leaking cam cover gasket and a peek inside) I could measure NO (repeat: NO) bore wear nor ring leakage anywhere. When I tore it down again at 136k miles in 2013 because of bearing wear due to a worn oil pump, I bored it as I already had the pistons and rings (from 121k miles) and didn't want to do it again. I'm sure it will outlive me, now!

[HondaMan]

Not to highjack this thread but I also trying to decide what rings to get

It's a 76 cb750 stock with 300 pistons and head. With just shy of 10000 miles on it.

With a bore dial gauge i measure between 0.0005 in to 0.001 inch difference in any sleeve in any direction. Gauge zeroed at 2.401in with a micrometer. Also checked the accuracy of both with few feeler gauges.

The rings stuck on the two pistons and I can't get those out. So I was looking at two options:
1) Standard RIK rings from Yamiya plus used set of pistons from eBay
2) standard cruising image kit of pistons with rings. Not fan of this option just because they are aftermarket and read on here that some folks have had issues with rings not sealing well.

Per Hondaman last post sounds like I have another option.

3) non chrome rings (cruising image?) with used eBay pistons? Would this be best choice?

Thanks

Well, at the very least you MUST stay with the pistons you now have (and in their same bores) or nothing will fit back together and run very well. The struggle is with getting new rings to seat in non-round bores: in order to get them to wear in far enough to seal, the bores must be heavily honed. This, in turn, will wear down the already-smaller piston skirts to the point beyond their ability to hold the rings stable (i.e., square to the bores), and oil burning results because the ring gaps get too big and the bores are not round anymore. This isn't just the SOHC4 engine: this is similar with all engines.

I've had great results with the CruisinImage piston sets and rings, IF the bores are properly done and the clearance kept tight: I use 0.0008" clearance after honing for the typical 750 (half that much for the CB350F engines), which many shops will refuse to do because it is considered 'precision' work. Not so, really: it just takes some extra care in setup, but that's what many riders find when trying to rebuild these bikes. If you have a good local machine shop you should be able to get this done without having to send everything here.

If you get the Cruizinimage set and want them done here, it costs  $35 per hole for boring, plus they will clean the cylinders like new, ready for paint, for $40, and mill the top deck down the required 0.010" for $40. This top-of-cylinders milling is required now because all head gaskets made since the 1990s have to use something besides asbestos in them, so they are all thicker. The OEM gaskets were 0.8mm thick and the modern ones are 1.0mm thick (unless you get CycleX or other MLS gaskets, which are even thicker yet) and this extra thickness makes the oil ports at the back of the cylinder leak oil as soon as the engine is started back up again unless thicker O-rings are used - they are NOT in any gasket kits, either. You can find those episodes all thru the build threads here: I can send you 2 new, thicker O-rings for those oil ports to prevent this, and you need to use them when reassembling the head to the cylinders.

Shipping back-and-forth depends on where you are: I live in Colorado, near Denver.

[PeWe]

Cruizinimage 392 (K7-K8)pistons will improve the compression.

My K2 got them, +0.50mm. Compression +20PSI from 150 something to 170 PSI.
150, 150, 150, 160 to
170,170,170,180.
I should have measured all chambers in head and made them equal. 4 must be smaller.

Oil level in tank moved very litte in tank during 5000km.
Last change after 5500km, oil looked and felt good, (viscocity). Spectro HD 20W-50.
Not much lower on dipstick.

[xhevi]

I thought 392 pistons and 300 head do not match. Either hitting the valves or not the correct CR. I have a k7 cylinder block with the 392 pistons that I could just re-ring if I don't have to mess with the head.

I want to keep it simple. The head and valves are good and rather keep it stock.

My intent was to rebuilt with the original parts, but with the piston rings fused stuck in 2 pistons also dropping the cylinder block and breaking two fins I have to sort it out.

Another issue is that I have not found any shop around me that deals with small engines. They mostly service car and truck engines. I am just north of the NYC and like everything else any service is overpriced.

From what I gather:
1) needing new pistons i need to overbore.
2) since I have overbore i need to decide the next overbore ( maybe 836)
3) If I have to overbore I could use the k7 cylinder block with intact fins and painted.
4) was thinking to get the cycle x gasket kit. I used it on my k7. That kit comes with all the rings and seals. I would guess cycle x kit comes with the thicker ring that Hondaman is referring to (or there is no need for thicker oring with the MLS head gasket)

And last but not least, my apologies to the original poster. I hope you got your answer.

[Pbeattie89]

I thought 392 pistons and 300 head do not match. Either hitting the valves or not the correct CR. I have a k7 cylinder block with the 392 pistons that I could just re-ring if I don't have to mess with the head.

I want to keep it simple. The head and valves are good and rather keep it stock.

My intent was to rebuilt with the original parts, but with the piston rings fused stuck in 2 pistons also dropping the cylinder block and breaking two fins I have to sort it out.

Another issue is that I have not found any shop around me that deals with small engines. They mostly service car and truck engines. I am just north of the NYC and like everything else any service is overpriced.

From what I gather:
1) needing new pistons i need to overbore.
2) since I have overbore i need to decide the next overbore ( maybe 836)
3) If I have to overbore I could use the k7 cylinder block with intact fins and painted.
4) was thinking to get the cycle x gasket kit. I used it on my k7. That kit comes with all the rings and seals. I would guess cycle x kit comes with the thicker ring that Hondaman is referring to (or there is no need for thicker oring with the MLS head gasket)

And last but not least, my apologies to the original poster. I hope you got your answer.

No problem. I did find a set of rings for my bike. They are RIK rings, so not the best choice, but I'm going to use what I've got. From what I understand, it should run just fine, but I'm likely going to lose some compression and longevity. If I still have the bike in a few years, I will likely do an 836 or possibly bigger kit.

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[HondaMan]

I thought 392 pistons and 300 head do not match. Either hitting the valves or not the correct CR. I have a k7 cylinder block with the 392 pistons that I could just re-ring if I don't have to mess with the head.

I want to keep it simple. The head and valves are good and rather keep it stock.

My intent was to rebuilt with the original parts, but with the piston rings fused stuck in 2 pistons also dropping the cylinder block and breaking two fins I have to sort it out.

Another issue is that I have not found any shop around me that deals with small engines. They mostly service car and truck engines. I am just north of the NYC and like everything else any service is overpriced.

From what I gather:
1) needing new pistons i need to overbore.
2) since I have overbore i need to decide the next overbore ( maybe 836)
3) If I have to overbore I could use the k7 cylinder block with intact fins and painted.
4) was thinking to get the cycle x gasket kit. I used it on my k7. That kit comes with all the rings and seals. I would guess cycle x kit comes with the thicker ring that Hondaman is referring to (or there is no need for thicker oring with the MLS head gasket)

And last but not least, my apologies to the original poster. I hope you got your answer.

I just finished a 750K4 engine that came to me with the CycleX gasket kit the owner wanted to use. It does NOT have extra-thick O-rings for the oil ports. It also has a normal (looked like the one in the Vesrah kits) head gasket. The MLS gaskets are even thicker, so they need thicker O-rings, too. This is true for 100% of the head gaskets on the market since about 2002. It's not the gasket maker's error: they are using the OEM specs. It is the head gasket maker's issue, since they can't use asbestos in gaskets sold in the Western marketplaces. That forces the head gaskets to come out thicker in order to be strong enough.

[Pbeattie89]

Not to highjack this thread but I also trying to decide what rings to get

It's a 76 cb750 stock with 300 pistons and head. With just shy of 10000 miles on it.

With a bore dial gauge i measure between 0.0005 in to 0.001 inch difference in any sleeve in any direction. Gauge zeroed at 2.401in with a micrometer. Also checked the accuracy of both with few feeler gauges.

The rings stuck on the two pistons and I can't get those out. So I was looking at two options:
1) Standard RIK rings from Yamiya plus used set of pistons from eBay
2) standard cruising image kit of pistons with rings. Not fan of this option just because they are aftermarket and read on here that some folks have had issues with rings not sealing well.

Per Hondaman last post sounds like I have another option.

3) non chrome rings (cruising image?) with used eBay pistons? Would this be best choice?

Thanks

Well, at the very least you MUST stay with the pistons you now have (and in their same bores) or nothing will fit back together and run very well. The struggle is with getting new rings to seat in non-round bores: in order to get them to wear in far enough to seal, the bores must be heavily honed. This, in turn, will wear down the already-smaller piston skirts to the point beyond their ability to hold the rings stable (i.e., square to the bores), and oil burning results because the ring gaps get too big and the bores are not round anymore. This isn't just the SOHC4 engine: this is similar with all engines.

I've had great results with the CruisinImage piston sets and rings, IF the bores are properly done and the clearance kept tight: I use 0.0008" clearance after honing for the typical 750 (half that much for the CB350F engines), which many shops will refuse to do because it is considered 'precision' work. Not so, really: it just takes some extra care in setup, but that's what many riders find when trying to rebuild these bikes. If you have a good local machine shop you should be able to get this done without having to send everything here.

If you get the Cruizinimage set and want them done here, it costs  $35 per hole for boring, plus they will clean the cylinders like new, ready for paint, for $40, and mill the top deck down the required 0.010" for $40. This top-of-cylinders milling is required now because all head gaskets made since the 1990s have to use something besides asbestos in them, so they are all thicker. The OEM gaskets were 0.8mm thick and the modern ones are 1.0mm thick (unless you get CycleX or other MLS gaskets, which are even thicker yet) and this extra thickness makes the oil ports at the back of the cylinder leak oil as soon as the engine is started back up again unless thicker O-rings are used - they are NOT in any gasket kits, either. You can find those episodes all thru the build threads here: I can send you 2 new, thicker O-rings for those oil ports to prevent this, and you need to use them when reassembling the head to the cylinders.

Shipping back-and-forth depends on where you are: I live in Colorado, near Denver.

I just purchased a super gasket kit from cycle x, and it came with 2 choices for head gasket thickness, 0.030 and 0.040. I chose the thinner 0.030. I assume that the thinner gasket won't require thicker o-rings.

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[PeWe]

That thinner gasket must be MLS, multi layer steel. Stock o-rings will be good.

Head and cylinder surfaces must be flat and without scratches. Surface finish like grinded by grit 400.

Also notify if the rivets holding it together will land on a surface between head and cylinder.
It did for me. Test mount tighten head a little with gasket, off with head to see marks after rivets.

I drilled a small dimple in the center of each mark. 8-10mm drill,  ca 1.5 mm deep where both head and cylinder mating surfaces got marks.

I hammered the rivet flat as well.
Below drilled dents in head and 2 cylinder blocks.

Cylinder got too just for sure. I have other cylinder where the mating surface is wider. Plus another where rivet is outside mating surface

MLS need HD studs that are more rigid. MLS need higher torque to seal, 21-22 ft lbs. It will give after when crushing at around 27Nm, 21 ft lbs. You will feel when tighten head nuts when it suddenly goes easier, that is good. Tighten a little more.

If you feel it will crush at 21 ft lbs. Possible to reuse gasket if you need to lift head again. Viton layer ok fine to reuse, just tighten a little more next time

I reused a gasket last time, rather high compression 70mm bores.

Also thinner MLS.
One of the cylinders below, pistons have dent for plug.

I also use 2  o-rings for oil feed despite MLS has sealing surfaces.

[HondaMan]

Those thicker O-rings are free: just send me your address...