Topic: What are these little plastic pieces for? (CB350 Twin)

[Raul CB750K1]

I post this here because I know there are many CB750 snobs out there -among wich I'm proud to count myself- and I'm afraid that if I  post this in the "Other bikes" forum it will get no attention. Mr. Moderator, please allow this post here for a couple of days and move it there then.


There are just two small rubber or plastic pieces in the studs of the CB350. They appear in the parts list diagram, but have no number. Seems like they come with the studs.

They seem to be a blockage for an oil passage or something, but I really cant understand why just two. Are they suppoused to go at the top or at the bottom of the stud.

As Terry would have said, "I don't understandy".


Thanks in advance

Raul

[scunny]

hell I don't know but is there a corresponding gallery or milling in the cylinders or head to give you a clue ?

[Raul CB750K1]

Nope, they can slide all the way through the stud. Actually they were above if memory serves me well, and I put them below to avoid them getting damage.

Raul

[crazypj]

I think they are to locate cylinder, as the camshaft oil feed is at the back.
PJ

[oldbiker]

Hi Raul, Honda call them dowels. They are purely location devices to get the case and barrel in correct allignment. I have never seen them made of plastic and maybe the previous owner bodged them up.  If I need one (through damage or loss) I just turn one up on my Myford lathe.

[bryanj]

Hi Raul, there should be steel dowels on the studs at the base gasket to keep the cylinder in line with the case and again between the cylinder and the head for the same reason

[supersport_CB400F]

Dowels...I don't know the Spanish for the word but sit down have a San Mig and get some real one's instead of plastic parts 

[Raul CB750K1]

Oh, please, I know what a dowel is!!!!! Please look at the picture carefully; you will see the steel dowel and the small plastic piece -blue color- just protruding from the dowel. That's the part I'm talking about.


Raul

[bryanj]

Sorry Raul, my eyesight aint that good. Its now over 30 years since i last pulled a 250/350 and i honestly cant remember any plastic parts on the studs--but that dont mean they wernt there! Does the oil feed up the studs in question? if so i can only guess they are a restrictor of some type. if so i would expect them at the bottom

[Raul CB750K1]

That makes sense to some extent Bryan. But, who would want to restrict the oil feed to the head??


Let's see if this picture is clearer.


Raul

[Sam Green Racing]

Raul, your best bet is to PM Ohiocaferacer, he's into these twins.

Sam.

[bill440cars]

                       Sam's got the best advice to date. If it's supposed to be there Greg ought to know.
            Something was said about a restrictor. Well, if it is, it might be to slow the oil down coming
            down from the head to insure that the oil doesn't return too quickly (keeping plenty in the
            head at all times. Just a thought. Come on Greg.  Later on, Bill

[ohiocaferacer]

Hey guys......sorry for the delay in getting around to this one. Seems like since the weather has improved here in the midwest.......i'm spending alot more time on the bikes and less time inside at the computer. Rode the hell out of a couple of the bikes this past weekend.....with temps in the 90s.....Oh.....life is good!! LOL!!

Now.......those are rubber sleeves on the studs...its been a few years since I read something somewhere about the exact purpose of those. I was talking with someone about those white plastic disc between the finns of the cyclinder heads and asking about those.....which off topic...they are there to keep the finns from making a buzzing sound as the engine revs up to higher rpms. Somehow we got to talking about those sleeves......and if memory serves......they basically were there to restrict oil flow and increase oil pressure. Oil feed to the top of the head is thru the rear 2 corner studs. Also.....these outer studs deliver oil to the cam holders that attach to the side of the cam tower.

Hope this helps,
Greg
www.OHIOCAFERACERS.com

[Raul CB750K1]

Thanks for the help Greg. So, if I'm not wrong, the camshaft rests on plain aluminium bearings, and get oiled from small "funnels" and holes above the holders. So, if the front outer stud holes are suppoused to be the return path for the oil -gravity fed-, the idea is that the passage fills till the point that it overflows and the head gets full of oil, isn't it?

And lastly, where are the plastic pieces suppoused to be? In the bottom of the stud I guess... They appear in the parts list manual, have no reference number but the pictures shows them at middle height.


Raul

[ohiocaferacer]

Wow....now your really pick'n my brain. 

I'm not an expert on the oiling system, but yes the cam is supported or rests on the cam covers(pieces that hold the points and tach cable) that bolt into the side of the cam tower. Now....from what I understand about how the oil flows......the upper head is feed thru the rear 2 outer studs, which leads into the cam end covers, tappets and the internal passages within the cam tower. Once the oil has worked thru the cam tower it is then returned to the case thru the cam chain tunnel. This is why there is the bleed screw at the top of the cam tower at the rear on the points side....this is where you bleed the air out of a fresh motor to allow the oil to fill the cam tower.

Now...those rubber sleeves should be inside the dowels on the top outside corners...between the cyclinder and the head.

Been awhile since i've been in a motor.....and having to remember off the top of my head, but hope this helps,
Greg

[Raul CB750K1]

Wait a moment. The oil pump is in the front. It feeds the crankshaft bearings and have that "famous" plastic ball blockage on the lower crankcase. Shouldn't the oil pump feed the head through the front outer studs?

I will check it out this afternoon.


Raul

[ohiocaferacer]

I wish there was a motor in the garage tore apart....that way I could go out and double check. The last motor I rebuilt....to clean the oil passages, I took the nozzle of my parts washer and stuck it in the oil ports within the case to clean them and to see which way the oil flowed. From what I remember those 2 rear studs carried the oil north.

There should be 2 oval shaped divits in the upper case where the stud screw in....there is an oil hole within each one.

Maybe Hondaman can chime in.....and give some info.

Greg