Author Topic: My 750F2 project.  (Read 3268 times)

Offline Cb750r

  • SOHC Associate
  • Posts: 50
    • View Profile
Re: My 750F2 project.
« Reply #75 on: February 11, 2024, 11:38:24 PM »
I have never liked the floppy passenger pegs, and would have removed them ages ago except for the fact it’s the one bike my wife likes riding on as a pillion and this is the bike we will go for mellow cafe cruises on together.

So I undertook the task of making them less floppy, by making a Delrin washer that’s thicker so in the upright position it’s snug. I also made Delrin bungs for the end of the peg so when in the “down” position the Delrin plug butts up against the bracket at 90 degrees. The added benefit is that the Delrin should be a lot more gentle on the brackets paint so folding them up and down won’t be sanding the powder coat down.

Offline SteveD CB500K0

  • Administrator
  • SOHC Jedi
  • Posts: 4425
  • Ride on the Steel Breeze...
    • View Profile
    • Steve's Blog
Re: My 750F2 project.
« Reply #76 on: February 12, 2024, 06:30:42 AM »
Had to Google that…


Sent from my iPhone using Tapatalk
2022 Tiger Sport 660
1971 CB500K0

Offline Cb750r

  • SOHC Associate
  • Posts: 50
    • View Profile
Re: My 750F2 project.
« Reply #77 on: February 12, 2024, 06:40:54 AM »
Had to Google that…


Sent from my iPhone using Tapatalk

Same material a lot of modern bikes frame sliders or similar bike protection is made out of. It’s a very easy to machine plastic. I think non trademark name is Acetal plastic.

Ive made a variety of sliders and rear stand bobbins, bushings spacers step washers etc with the material.
« Last Edit: February 12, 2024, 01:59:56 PM by Cb750r »

Offline Cb750r

  • SOHC Associate
  • Posts: 50
    • View Profile
Re: My 750F2 project.
« Reply #78 on: February 14, 2024, 05:32:24 AM »
Well I went to speak with the shop that did the cylinder boring, they put on a grand show, measuring a cold cylinder and moving around so quickly as to not really show me anything but say all the right words to convince me they have done no wrong.

I got sick of this and purchased my own dial bore gauge and measured all 4 cylinders. And my machinist is right the very top of all the bores are on target… but sadly that’s as good as the story gets.

All cylinders are barrelled. All of them are the most narrow at the top of the bore and tighten up a bit right at the bottom. Unfortunately that leaves them at the most wide at points where piston velocity and side thrust are at the peaks if I’m not mistaken.

While I’m not a machinist I did my best to take accurate measurements and can see how easy it would be half a thousandth out. However I can consistently repeat measuring the inconsistency in the final bore.

I think these cylinders will make a great decoration and will have to get another set machined by a motorsports specialist. I’ve attached my measurements below.  Note I re measured #1 it does barrel as large as 0035, but comes back down to 0030. Have it written down that 0035 was at bottom but it’s not.






Offline Johnny4428

  • SOHC Master
  • Posts: 1950
    • View Profile
Re: My 750F2 project.
« Reply #79 on: February 14, 2024, 07:53:36 AM »
Not qualified to comment on these figures, thankfully I had mine done by one of the very knowledgeable and competent qualified guys on this forum. Hope you get it sorted.
1952 Cymoto on Triumph bicycle.
1961 Matchless G3
1974 Honda CB550K1. Running resto,
1978 Honda CB550K3.
1999 ST1100 Pan European 50th Anniversary.
1975,1980,1984,1986 Honda C90’s
1973 Honda CB750K3

Offline McCabe-Thiele (Ted)

  • Grogu
  • *
  • Posts: 5894
    • View Profile
Re: My 750F2 project.
« Reply #80 on: February 14, 2024, 08:38:26 AM »
I'm certainly no machinist - it did make me scratch my head as to  how you end up with a barreled shaped bore when using a boring bar of the right size range?

Bryanj will know.

Honda CB500 K1 (new pit dug out ready)
Honda CB400 four super sport (first money pit)
http://www.sohc.co.uk/index.php/topic,23291.0.html

Offline K2-K6

  • Grogu
  • *
  • Posts: 5187
    • View Profile
Re: My 750F2 project.
« Reply #81 on: February 14, 2024, 10:49:11 AM »
With no idea what their machinery is like, it's speculative to assess from me.

Usually associated with feed rate in general machining, the tool has to be buried into the material it's cutting, with a wedge shape of the base material being sheared out of its structure as the tool is forced through it in removal.
If the entrance feed was cautious to preserve face of bore, speeded up through mid part, then slowed for exit, this could produce a barrel effect. Basically with higher feed it has more aggressive cut width on each revolution, with the tool being "pulled" further into the wall as it travels with that difference in feed. Its a bit like stripping wallpaper, when you get too much angle on the blade and it's goes "oink~twang" taking a neat little triangle of your plaster with it  :)

You'll get it on a lathe too, with a longer tool extension being a little flexible if reaching a long way in. On that you try to offset that little wedge of removed material by grinding a back rake on top of tool face to minimise that wedge in size, the angle of attack effectively.

Drill bits in lathe headstock do it too, you have to go at it really slowly to stop the drill nose "walking" around in a circle if biting too hard, especially as it's likely there's imbalance across the drill cut blades from one side to another.

It shouldn't happen obviously from a good machine shop, often you'll see experienced machinists going about something in a certain way that may look odd, but experience in that process gives them ways to mitigate shortcomings in process.

Offline Bryanj

  • Grogu
  • *
  • Posts: 10618
    • View Profile
Re: My 750F2 project.
« Reply #82 on: February 14, 2024, 01:57:36 PM »
If those are sizes in thou over the size of the piston its been bored too big anyway

Offline Cb750r

  • SOHC Associate
  • Posts: 50
    • View Profile
Re: My 750F2 project.
« Reply #83 on: February 14, 2024, 03:12:44 PM »
.0025" is what JE calls for for these pistons.

From what I understand this is likely to bad honing setup/ technique. Either way these sleeves are toast as 65mm is max bore on stock sleeves.
 
I may try these on a cheap set of 65mm pistons in these if I build up all my leftover engine parts into a second engine some day. But these cylinders sure aren’t going together with all the expensive bits I’ve assembled for this build.

Offline royhall

  • SOHC Jedi
  • Posts: 3348
  • Keep biking I'm not quite bankrupt yet
    • View Profile
Re: My 750F2 project.
« Reply #84 on: February 14, 2024, 05:03:07 PM »
0.0025" is way too much for a Honda. At that it would burn oil for fun. Maximum on those is 0.001" and sometimes less than that. Plus they may not all be the same. Pistons should be allocated to a bore then measured for each bore. Fairly likely that the pistons are not all the same size. If you should get a slightly undersize piston on a 0.0025" bore you will hear the slap. As for the barrel effect, from my time as a machinist that is usually too high a feed rate. Rushing.

Sent from my Pixel 7 Pro using Tapatalk
« Last Edit: February 14, 2024, 05:05:38 PM by royhall »
Current bikes:
TriBsa CCM 350 Twin
Honda CB350F in Candy Bacchus Olive
Honda CB750F2 in Candy Apple Red
Triumph Trident 660 in Black/White
Triumph T100C
Suzuki GS1000HC
Honda CB450K0 Black Bomber
Honda CB750K5 in Planet Blue Metallic (Current Project)

Offline Nurse Julie

  • 1977 CB550/4 Mongrel Brat. 1974 UK 500/4 K1. Honda CD250u.
  • Grogu
  • *
  • Posts: 8157
    • View Profile
Re: My 750F2 project.
« Reply #85 on: February 14, 2024, 05:08:32 PM »
Agree Roy, that piston to bore clearance is massively over the top, like you say, 1 thou inch maximum on most aftermarket and down to 0.6-0.8 thou inch on genuine Honda pistons.
At 0.0025" that's almost old British bike spec where they use a lollypop stick to measure the clearance 😂😂😂
« Last Edit: February 14, 2024, 05:11:19 PM by Nurse Julie »
LINK TO MY EBAY PAGE. As many of you know already, I give 10% discount and do post at cost to forum members if you PM me direct.
https://www.ebay.co.uk/sch/julies9731/m.html?item=165142672569&rt=nc&_trksid=p2047675.m3561.l2562

LINK TO MY CB400/4 ENGINE STRIP / ASSESSMENT AND REBUILD...NOW COMPLETE
http://www.sohc.co.uk/index.php/topic,14049.msg112691/topicseen.html#new

Offline Cb750r

  • SOHC Associate
  • Posts: 50
    • View Profile
Re: My 750F2 project.
« Reply #86 on: February 14, 2024, 05:34:44 PM »
These are 2618 forged pistons, which require more clearance than other piston materials.
Also according to the measurements required which is .5” up the skirt this is closer to. .0020 measurd conventionally at the base of the skirt
. I’m not really debating the spec set out by the piston manufacturer. I am more concerned about the lack of workmanship and my Un usable cylinders.


Offline Bryanj

  • Grogu
  • *
  • Posts: 10618
    • View Profile
Re: My 750F2 project.
« Reply #87 on: February 14, 2024, 06:05:29 PM »
Roy, i disagree about piston sizes. If using genuine Honda, or even aftermarket i personaly have never found a measurable difference from quoted size, as to the big bore ones i dont know

Offline royhall

  • SOHC Jedi
  • Posts: 3348
  • Keep biking I'm not quite bankrupt yet
    • View Profile
Re: My 750F2 project.
« Reply #88 on: February 14, 2024, 06:11:05 PM »
That's fair enough, if your pistons are all the same size then the bores will be as well. But it would be a poor job not to check and just trust them. I've had two sets of aftermarket pistons that have been slightly different, they were machined to suit. Never had a difference on genuine though.

Sent from my Pixel 7 Pro using Tapatalk

Current bikes:
TriBsa CCM 350 Twin
Honda CB350F in Candy Bacchus Olive
Honda CB750F2 in Candy Apple Red
Triumph Trident 660 in Black/White
Triumph T100C
Suzuki GS1000HC
Honda CB450K0 Black Bomber
Honda CB750K5 in Planet Blue Metallic (Current Project)

Offline Bryanj

  • Grogu
  • *
  • Posts: 10618
    • View Profile
Re: My 750F2 project.
« Reply #89 on: February 14, 2024, 07:29:41 PM »
Years back we bought our pistons from a man on a van and his were all Art who i believe made the o.e. honda

 

SimplePortal 2.3.5 © 2008-2012, SimplePortal