Topic: Pistons and capacity - now I'm really confused

[RupertB]

OK - story goes that the 750 I have might have a Yoshi 810 on it. A previous owner has had the log book amended to say 810cc - I know this is in no way proof, but it means if it is bulldung then it was a comprehensive self-delusion.
So, I strip the top end and find the pistons are about 63.6mm across - I say about as I am not the most accurate measurer, but it is with a vernier thing and it certainly isn't the 61mm that would equate to standard 736cc. Now the pistons have one scraper ring and two compression rings, and have 'HONDA' cast into the slight recess by the gudgeon pin. (Logical really because if it wasn't in the recess it would makea nasty mess of the bore!). So could it simply be an oversize piston set? Well from what I can find, no. 4th oversize is at 62mm which gives 761cc, and these pistons are definitely well over 62mm, AND they have the letters STD stamped into the crown - same pattern on each piston. Now I really don't care if it is a standard engine - they're great engine just as Mr Honda made them, but these pistons can't be standard - can they?
The only oddity in the pistons is that the 'A' of HONDA on each piston is slightly higher than the preceding 'HOND'.
Anyone any ideas, suggestions etc - because it is going to be a swine getting new rings for them if I need them!

[MCRider]

I'll just throw out a bunch of Cr-p until someone who knows can answer. Did you measure your pistons at the skirt or at the ring level? Measure at the skirt would give a higher bore measure and that's what counts.  They would need to be 64mm to = 811cc. (back in the day 810,811, and 812cc were tossed around)
http://www.nightrider.com/biketech/calc_displacement.htm

There wouldn't be 2 compression rings, the top is compression, the second is scraper and the lowest ring should be an oil ring, though it could be a one piece oil ring. Having slots cut in it to pass the oil.

Some of the earliest big bore kits were made with CB350cc slugs, so (I think) they could be marked STD as applies to a CB350. Again I am working from a distant memory of things that were, or might have been. Hope you get better confirms.

[754]

Yup measure at bottom of skirt, on the thrust face, keep in mind you have a thou or + clearance, plus wear.. they should be around 63.9ish..

 Some Yosh pistons were slipper pistons.. short skirt & life..

 Good news if its worn, you can cleanup bore to 836cc.

[Big Jay]

If the pistons say Honda, it is not a Yosh. The Honda is because it was made from a CB350 twin piston. I made a few, but not many. Could be an Action fours.

[RupertB]

I think the term 'throw out a bunch of Cr-p until someone who knows can answer' is a bit strong - I prefer 'give as comprehensive a picture of possible and allow the more knowledgeable to have their say.'

So here's a bunch more cr-p for someone to answer....

Finally got a few miinutes in the garage and removed a piston, whereupon I get more confused. Here's why - I measured the base of the skirt in the 'fore-aft' plane (at 90 degrees to the gudgeon pin) and got 63.95mm. Fair enough.
The recess below the gudgeon pin on the outside of the piston says HONDA, but cast into the inside of the piston at various points around the inside  is the following -           TOHO              CB810          HA-64

I'll cut it short now - anyone able to shed light on the origins?

[Ricky_Racer]

Henry Abe 64mm 810cc???  RR

[Terry in Australia]

Henry Abe 64mm 810cc???  RR

Yep, my thoughts exactly, a Henry Abe 810 Kit. Old Yoshimura stuff had "Pop Y" stamped/cast into it. Cheers, Terry.

[RupertB]

Don't you hate it when the obvious hits you in the face - It has just dawned on my dull brain what the 'HA' part of 'HA-74' might stand for!
Thanks fellas. Any idea when that might date from and if there are any suitable replacement rings? I have yet to get a knowledgeable opinion on the pistons and bores - they don't look too bad but given that I can't spot what HA might stand for I'm not going to trust my own judgement!
If the worst comes to the worst then it is a matter of moving up to 836cc or thereabouts, so apart from cost, life could be a lot worse!

[754]

Stock CB 350 rings I believe.
May come wiyh 1pce oil rings, should get you thriogh a season..

[RupertB]

Just had a very helpful email from Actionfours after I sent them a pic and info on the 64mm pistons -

'The piston you have was sold by the Henry Abe Company, made by a small
piston manufacturer, Toho.

I regret to advise you that this is a non-standard (oil) ring size
(thickness) "cheapie" kit that rings have not been available for in around
25>30 years'.

So, unless someone out there has a set of unused rings or oversize HA-74 pistons (anyone?) then I can feel a rebore coming on. Any suggestions on whether there is something just big enough to take out any suspect bits on the bore, or is a Wiseco 836 a better-proven way to go? At least that way it is a fresh start and a very well-trodden route.
Any alternative suggestions - CB350 pistons seem a bit of a fudge, or am I bigoted?

[Flying J]

Why does action 4 get pictures and we dont?

[bwaller]

If the 350 twin oil ring is wider than the HA pistons you could get the oil ring groove cut wider.

[Terry in Australia]

Yep, what Brent says, it's pretty easy to machine the pistons to accept 3 piece oil rings, if you need them, and if you can find the rings you need.

Having said that, I'm running 30+ year old Arias/RC 836cc pistons in my 836cc engine and they've only got single piece oil rings, but after plenty of 9000 RPM (+) runs, it doesn't blow any smoke, although Steve K0 thought he saw a wisp of blue smoke from the pipes once as I was decellerating hard.

I think people get a little too concerned with 1 piece oil rings, (if you've got an original untouched K0/K1 you're running single oil ring pistons) but I understand that a 3 piece setup is better again. The 110 dollar 836cc kits I bought on EBay from Japan might be a nice cheap alternative to a Wiseco kit mate, and of course, they have 3 piece oil rings. Cheers, Terry.

[RupertB]

Plenty to think about - in a hurry this morning but some piston pics now on at http://s1179.photobucket.com/albums/x397/rupert2147/

[Big Jay]

Those are HAs, not 350 Hondas. The problem with them is they generally used oil rings thicker than anything available.

[Jerry Rxman Griffin aka MuthaF'er]

You haven't posted the ring thicknesses yet?! May be an easy ID if you'll provide those numbers. 

[RupertB]

From the top the rings are 1.5, 1.5 and 2.5mm - emailed action fours who reckon you migt be able to machine the grooves wider to accomodate modern ones, but for that money I could go for the cheapie 836 and have a clean slate I suppose, especially since at the least the bores need honing, and if they need a rebore then the HAs are pretty much useless. And CB350 pistons would cost more than the cheap 836s. What a series of options!
Anyway a firm in Gloucestershire UK (Saunders I think they are) reckon the R10 on the camshaft is a Yoshimura marking which is reassuring - unless anyone out there knows more? It certainly has a long lift and steep closure profile. Will try to get a good photo of it and post that.

[Jerry Rxman Griffin aka MuthaF'er]

Stock CB350 Twin rings. 1968+. Same as my 810 Yoshimura pistons. 

[RupertB]

Many thanks - I am getting the barrels and block blasted and generally cleaned up over the next few weeks, then I'll get an opinion on the bores so that will be decision time. Many thanks to everyone  for the info and help - I now have a full range of options in both technical and money terms, which as you probably all notice is way better than me trying to work things out for myself. I keep this updated as things go on.
Incidentally saw a wonderful pair of forged magnesium wheels on the internet - rang about the price..... £2800!! Maybe later....

[Jerry Rxman Griffin aka MuthaF'er]

Just took a look at my Yoshimura Daytona cam. I brought it new in 1976 so I'm sure about what it is. It is a R9 blank. These R9/R10 mean NOTHING about the grind. They are all made by/for Honda and apparently Yoshi used the same supplier as Honda then ground it themselves or had it done to their specs. It has the letter "B" stamped into the end with the timing marks whereas my other 2 stock Honda blank cams have nothing there. I can get you a 25,000 mile lobe height if you'd like once I find my calipers.

[lordmoonpie]

From the top the rings are 1.5, 1.5 and 2.5mm - emailed action fours who reckon you migt be able to machine the grooves wider to accomodate modern ones, but for that money I could go for the cheapie 836 and have a clean slate I suppose, especially since at the least the bores need honing, and if they need a rebore then the HAs are pretty much useless. And CB350 pistons would cost more than the cheap 836s. What a series of options!
Anyway a firm in Gloucestershire UK (Saunders I think they are) reckon the R10 on the camshaft is a Yoshimura marking which is reassuring - unless anyone out there knows more? It certainly has a long lift and steep closure profile. Will try to get a good photo of it and post that.

That'll be Bernie Saunders of B&C Saunders - the man who maintains the Beaulieu museum Hailwood Honda -4 and knows, well, everything about classic hondas. If you want those piston grooves machining pout to accept modern three piece scraper rings you could do worse than talk to Steve at Dynasurf in Ettiley Heath near Sandbach. They machine all types of stuff there and would do that for you as a small job, cheap price I'm sure. Whereabouts in Cheshire are you?

[Jerry Rxman Griffin aka MuthaF'er]

Rupert - see your other topic for cam measurements

[RupertB]

The height of the lobes is in the region of 36.85 - 37mm according to my Aldi caliper.
Should be an end view attached - they don't look like cooking lobe profiles to me.
Am in Frodsham Cheshire by the way.

[bwaller]

I thought I might help with CB350 ring thickness but the oil ring is missing from the box...sorry. Top two will fit though.

It may not mean much but I have a set of HA 61mm pistons in a CB550 and the top two grooves were identical to standard CB750 pistons. The oil ring they used was narrower than the 750 piece so I was able to widen that groove and use Honda rings, that's why I mentioned it.

Like you say at least you have options.

[RupertB]

Based on nothing more than supposition I imagine that while Abe pistons may well be made to his own design and commission, it is very likely that he would buy in rings from a proprietary source, given the relatively small output, and a reasonable bet is they would come from the Honda parts bin. My unknown at the moment is whether the pistons and bores are in any was reuseable, and given that the motor sat unturned for perhaps 15 years or more with the plugs out, outside but under a tarpaulin, I would guess an overbore is the most likely sensible requirement. All part of the excitement of a rebuild. My bank manager can hardly wait!