Topic: Question about Honda single , 500?

[754]

Got a head in to work on today, I think I have to make headbolts.. or repair them.

It got dropped off without 2 much info by a 2nd party.

The headbolts  have spiral grooves rolled into them, what is the function of these??

[Uncle Ernie]

They channel water away and give the socket better traction.
















pictures?

[crazypj]

I think they are to allow the bolts to stretch and recover slightly as the engine heats up/cools down.
 I'm guessing your talking about the later RFVC motor and not the early XL?
 The head is bolted to the block and the block is bolted to the crankcase so it doesn't have the more usual long studs clamping everything together.
PJ

[mark]

From page 1-10 of the Honda Common Service Manual:

"Certain areas of the m/c or scooter are subject to repeated and severe external forces. Special bolts with a high percentage of elastic deformation capability are used in these areas. [drawing of special groovy bolt] Installing common bolts in these areas with special requirements may lead to loosening or shearing of the fastener."


Good luck.

[754]

Yes, no thru studs, and a fu-fu valve on the top of the head where the cam split is.

Interesting valve arrangment and rocker, I assume it is because the valves are canted.

I will take a good look at it all, looks like a few were helicoiled, but I think they still had trouble..The owner is a toolmaker, I will go over it with him.. make him aware of the higher stresses these bolt take..

[754]

Well looks like these have short bolts near the camchain cavity, really short in the middle, then the longest on the 2 holes furthest from camchain cavity.

Here is the problem , one of the 2 outer holes is helicoiled, and I think too far down..about 1.25 or more down to top of helicoil in a hole about 10mm dia... so stock bolt may not engage enough thread & I dont think I can get helicoil out

So I am thinking to make a hard aluminum insert in the top of those 10mm (at the top of the  holes), then tap 8x1.25, then run same bolts as other side or put a spacer under the heads of the 2 long ones..

 anyone played around with these before??

[bryanj]

Used to be things called "keenserts" but you need a lot of metel arrround them, also heard of timeserts

[troppo]

i just did a google and those time-serts look damned good

[754]

The holes are counterbored to about 10.5mm  the thread is 8mm.

If I tap to 12mm or 1/2 coarse, then make a snug fitting insert, and tap internally to 8mm, I think it will work. I would use 7075 bar whiich is a lot stronger than the stock castings ever were..

[crazypj]

Its been quite a while since I worked on one (originally 1980~81, then did XR400 to 440 kit about 5 yrs ago)
If I remember right, there are two 8x1.25 studs sticking out of head but I thought they were 10mm shouldered on the piece that actually screws into head? (double diameter stepped studs)
 The bolts on outside next to cam tunnel are 7x1.00mm
 The weird bolts are 10x1mm I seem to remember (had 2 stripped on my XR)
 Can you get a pic posted ( or link to one?)
 The reed valve is to prevent charge robbing.
You have an early(ish) version which originally used two carbs, one for each valve/intake.
 Honda found the mixture wanted to go from the left side inlet tract into the right side until the right side carb started opening (was designed to give higher gas velocity though single small valve and more torque at low rpm) Later models had single large carb and common intake.
PJ