Topic: 836 pistons claiming rc eng.

[Ephesmax]

http://www.ebay.com/itm/NEW-69-78-HONDA-CB-750-CB750-COMPLETE-CYLINDER-PISTON-KIT-836CC-BIG-BORE-KIT-/290759601839?pt=Motorcycles_Parts_Accessories&hash=item43b29f6eaf&vxp=mtr#ht_626wt_689

So this seller is claiming to have RC engineering piston but I thought they stopped making pistons can anyone shed some light?

[Xnavylfr]

Where's the proof they are RC pistons???  There are currently some JAPANESE made 836 kits on E-BAY for half that price!! Very good kits, installed 1 in a buddy's bike and no problems.
I would ask for documentation to prove they are RC!!!!!


Xnavylfr(CHUCK)

[kmb69]

Those do appear to be the "RC" piston kits machined from Honda 350 twin pistons. Similarly modified 350 pistons were also sold by Action Fours and others. This big bore kit was very common back in the day. Anybody with a Bridgeport mill and a fixture could machine a 100 a day. They have a higher compression ratio than the 1/2 price Japanese kit mentioned. Probably about 10.5 : 1 in a K head.

[Greggo]

Those sets have the 1 piece oil ring.  The pistons do look nice though!

[MCRider]

RC Eng as in motorcycle parts is long defunct.  So when they say "new" they mean "NOS" - New Old Stock. As in never used still in the box, but maybe really old.

The bike in my avatar, built in 71/72, had the Action 4s, reworked CB350 pistons in it. Those were "new". 

[Greggo]

My question with these would be if the groove has to be machined to accept a 3-piece oil ring?

[Jerry Rxman Griffin aka MuthaF'er]

Well they do have RC cast inside them and if the oil land is 2.5mm then the 350 twin 1mm over 3 piece rings will work

[kmb69]

Well they do have RC cast inside them and if the oil land is 2.5mm then the 350 twin 1mm over 3 piece rings will work

Jerry,

You just made me take a closer look. Those are NOT the remachined 350 pistons. My previous post is WRONG. They are later model GENUINE RC castings.

Keith

[Ephesmax]

So they will accept a 3 piece oil ring? They are forged, cast, good for a build thats not a race bike, crap, junk. Clue me in?

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[kmb69]

They are cast. Don't know if the 3 piece oil ring will fit. Should work just fine in a street bike. You will need to jet properly. While the 3 piece oil rings may be better, the 1 piece rings were used effectively for years.

[Xnavylfr]

I didn't notice an RC casting mark but I'm 61 and have CRS and NOASSATOL.

They do look (TO ME) that the dome is a little tall compared to a stock piston but what do I know???After looking closer they don't look TOO tall.

Xnavylfr(CHUCK)

[Greggo]

I emailed the seller about the oil ring groove, asking if he could measure it.  They replied that the 1-piece ring is better, and they didn't know if 3-piece rings would fit. 

I have seen the 'RC', but not 'RC ENG' stamped in an earlier set of pics this guy had, but now that pic is gone, and you can only see in one angled pic the 'RC' but nothing after that as the edge of the skirt blocks the view  

Did all RC Engineering pistons have just 'RC' cast inside, or the 'RC ENG'?

[Ephesmax]

At the risk of asking a newb question cruzinimage or these which is a better made part?

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[Terry in Australia]

Those pistons are genuine NOS RC Engineering branded Arias pistons. I've got them in my K1, and they're great. People make a big thing about one piece oil rings, but unless your "piston to cylinder wall" clearances or ring gaps are excessive (i.e., if your engine is worn out anyway) it won't smoke.

Don't forget, until around 1972 or 1973, Honda ran one piece oil rings in most of their 4 stroke engines including CB750's, so it's possible that some folks here are running them and don't even know it. For the money, they're much better quality than the cheaper low compression 836cc kits currently on EBay.

I need to rebuild my K1 engine soon, (the pistons and cylinders were used when I bought them and have done a lot of 11000 RPM passes, and the clearances were on the limit when I built this engine 7 years ago) but I'd have no hesitation buying another set. Cheers, Terry.

[Ephesmax]

AWESOME TERRY TY VERY MUCH

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[chewbacca5000]

Those pistons are genuine NOS RC Engineering branded Arias pistons. I've got them in my K1, and they're great. People make a big thing about one piece oil rings, but unless your "piston to cylinder wall" clearances or ring gaps are excessive (i.e., if your engine is worn out anyway) it won't smoke.

Don't forget, until around 1972 or 1973, Honda ran one piece oil rings in most of their 4 stroke engines including CB750's, so it's possible that some folks here are running them and don't even know it. For the money, they're much better quality than the cheaper low compression 836cc kits currently on EBay.

I need to rebuild my K1 engine soon, (the pistons and cylinders were used when I bought them and have done a lot of 11000 RPM passes, and the clearances were on the limit when I built this engine 7 years ago) but I'd have no hesitation buying another set. Cheers, Terry.

Hi Terry,

Which do you think is better this kit or Cycle X 849 kit same price?

[Terry in Australia]

I've never used the CycleX kit mate, so I don't know, but I imagine that the quality is good, and if it comes with a head gasket, you'll save some bux as the RC kits don't come with the special head gasket, so you'll need to spend another 20 or 30 bux for one from Z1, CycleX, Dynobike etc.

My only concern with the 849cc kits is that they were initially a cheap fix if your 836cc kit was worn out and you couldn't get some new sleeves. Keep in mind that you've already removed 4mm from your sleeves to get them out to 836, and now you need to remove another .5mm from sleeves that are only around 2mm thick.

I honestly don't know what's safe when it comes to cylinder wall thickness in an aircooled engine, but I'd rather buy the RC kit, even though it'll have those hateful single piece oil rings. Cheers, Terry.

[PeWe]

I have bought these pistons. Not installed yet, but I'm very positive.
It's molded pistons with markings inside: RC   HP6450

I recommend this eBay seller when the shipment was very quick and very low shipping cost. The only thing missing is the piston pin clips. I have purchased OEM which fit well.
The rings grooves in the piston same as RC (forged) pistons and Action Fours that I have compared with.
Rings from old CB350 Twin +1mm match which I have read iwas used in AF836 pistons as std. 3 pieces oil ring available.

I have written about these pistons on this forum, comparing them with other pistons mounted in the engine:  http://forums.sohc4.net/index.php?topic=104925.msg1187359#msg1187359
They are the "new pistons"

[mycb750k6]

Can you explain why these are better than the cruzinimage 836 flat top pistons? I have no doubt they are but I'd like to understand why. No doubt they have more compression which isn't always the best thing but beyond that what makes these more desirable?  Also what cylinder clearance is needed when boring the cylinders, .012? And finally since there are no keepers, can I just machine some nylon keepers like the old time RC pins had?

[chewbacca5000]

I've never used the CycleX kit mate, so I don't know, but I imagine that the quality is good, and if it comes with a head gasket, you'll save some bux as the RC kits don't come with the special head gasket, so you'll need to spend another 20 or 30 bux for one from Z1, CycleX, Dynobike etc.

My only concern with the 849cc kits is that they were initially a cheap fix if your 836cc kit was worn out and you couldn't get some new sleeves. Keep in mind that you've already removed 4mm from your sleeves to get them out to 836, and now you need to remove another .5mm from sleeves that are only around 2mm thick.

I honestly don't know what's safe when it comes to cylinder wall thickness in an aircooled engine, but I'd rather buy the RC kit, even though it'll have those hateful single piece oil rings. Cheers, Terry.

Thanks Terry!  Much Appreciated.

[PeWe]

Can you explain why these are better than the cruzinimage 836 flat top pistons? I have no doubt they are but I'd like to understand why. No doubt they have more compression which isn't always the best thing but beyond that what makes these more desirable?  Also what cylinder clearance is needed when boring the cylinders, .012? And finally since there are no keepers, can I just machine some nylon keepers like the old time RC pins had?

- Higher compression make a lot of more fun when twisting the throttle.
- Cylinder clearance is described in this forum in several threads. Just search. Different forged vs molded pistons.
- OEM style of piston pin clips is what the pistons are made for. Cost just a few bucks.

[ant398]

Hi,

Quick question, has anyone had any experience with using this particular piston kit in an F2 application?  If so, what, if any mods/machining were required to make it work?

I'm planning on freshening up my 77 F2 and am exploring my options should my standard bores/pistons measure out of spec after teardown.

Any info is appreciated in advance.

[Terry in Australia]

First of all, no mate, I haven't used them in an F2, but I think they'd work well in that application as they have a high dome like an F2 piston, so they'd fill the larger F2 combustion chamber better than the flat top 836cc EBay Pistons, and you wouldn't lose much if any power, due to a much reduced compression ratio like you would with those flat tops. Cheers, Terry.

[ant398]

Thank You Terry.