Frame repairs Bore and Bush or weld and grind?

[topari]

This is a frame from an 85 KDX200. The top linkage mount has been abused and is now oval instead of round.
How should this be repaired ? The bore and bush is easier said than done and weld and grind could also be difficult.
The pictures show the extend of the damage.
What do people think ?



This picture show the extend of the problem. That plug may become a fixture for boring. I think an annular cutter of some 20mm will do the job. Then I will bush.

[Lozza]

Whack it on ebay    Not sure what a annular cutter is but a end mill or a D bit could get that back to concentric. Think your idea of a long machined guide for the drill/cutter would be the only way to do that. Be interested to see how it turns out. The sides of the bush are rather thin

[Slakewell]

You need a tapper reamer with an extension guide to the other side to hold it in the center,. ream it to over size and insert bush made from 404 steel.

[KTM47]

If you (or a machine shop) can get it onto the bed of a vertical mill and the outside of the original boss welded into the frame is true enough. The mill head could be centralised on that boss and then bored out with a end mill or slot drill. Then make a bush to suit and if necessary weld it in.

If you have a friend who is a Fitter Machinist it will help.

Take it to a machine shop and see what they think. Don't commit until you have a price.

[brucey]

Simple mate you have the counter bored side of the lug.

How I would tackle it take a 50 mm slug of mild steel 50 mm long machine the nose to a tap fit into the counter bore and ensure that the nose is level with the depth or a mill less it must bottom on the cleaned up flange and drill and bore it 20mm through that's your reaming bush sorted

Grab a 3/4 adjustable reamer and ream it through increase the size until you remove enough of the ovality to suit your new bush and bung her in

there are some assumptions here, by the look of it you have access to a lathe (turned up Bung) and can access a set of adjustable reamers do you have mates / access to a set or for 100 bucks get a set for life http://www.ebay.com.au/itm/NEW-ADJUSTABLE-HAND-REAMER-8-PCS-SET-15-32-1-1-16-CARBON-STEEL-BLADES-/151159869564?pt=LH_DefaultDomain_15&hash=item2331d4907c

Yes they are made in india but if you look after them and cover them in cutting lube they will last a life time

Good luck with it

[topari]

Good responses. The bung or plug is a tight fit. The hole is a 5mm guide for the pilot pin on the annular cutter, which is my current thinking. These annular cutters or rotabroach, as they are commonly called cut dead accurate. I have had a few test runs on some 10mm steel and these cutters are amazing. I like the reamer approach. I'm going to spend the next hour or so trying to figure out how to secure the frame to either the mill or the drill. This may force me one way or the other.

Sincerely,
Tom

[GMC]

Your thinking about it too much, it’s not a bearing surface, it only holds the bolt in place as the bearings run in the rocker arm.
It is worn upwards as this is the direction of pressure and the plate that the hole is in is only thin.
I would weld it only around the worn part and then carefully grind it back until the pin fits in snugly. It may take a couple of goes to get it right.

As the hole on the bottom part is in the correct position you use this as the base to work from, don’t weld or grind this part.
This is where reamers can stuff it as they will cut a new hole but they will offset the hole as it finds the easiest way.
Mills are all well and good but something like a frame is really hard to bolt down tight and square and if it is not held down tight then it will chatter.

[TM BILL]

Whats the worst can happen if its a couple of mm out its a dirt bike, your not going to be tearing around Phillip island at 300 kph 

I would have thought that any discrepences would right themselves through the various links etc 

[evo550]

I would just go with a washer that has the same I.D as the bolt and the same O.D. as the frame hole, get a slightly longer bolt and your away.

[topari]

I would just go with a washer that has the same I.D as the bolt and the same O.D. as the frame hole, get a slightly longer bolt and your away.

Not a silly idea. 

I can secure the frame on the drilling machine. I will try a dry run tomorrow.
I have this ideal by which I undertake my projects.  Aim for perfection, even if its not required, because the next project may demand it and at least I have prepared myself.

[Tomas]

 You can also fill the holes with weld and start fresh. Use slot or flat end drill to clean the bottom face of the counterbore. Than use some bush or bung with a correct outside and hole diamater that will lead,center your drill to get nice fresh and round holes with minimal runout.
Hope it helps.
Tomas

[Mick D]

It is always nice to admire skills perfectionism, but

Your thinking about it too much, it’s not a bearing surface, it only holds the bolt in place as the bearings run in the rocker arm.

Exacery, a perfect scenario to demonstrate the KIS principle.

I would just go with a washer that has the same I.D as the bolt and the same O.D. as the frame hole

Don't loctite the nut back on, this is something that should be checked for torque tension regularly, particularly on a dirt bike. If there is not quite enough thread left for a self locking simons/nyloc nut, just face spin enough of the bottom of the nut so the nylon collar engages the thread. Back on the track real quick and last forever if kept tight.

[Lozza]

Something like that should have the shank of the bolt supporting the load as well.

[SON]

I like the kiss principal
A good bush mechanic would Drill it, tap a spark plug thread into it,
Screw in the appropriate old spark plug
Grind off the leftovers
Then ream back to the required size
Who has reamers in their toolkit anymore?
My Dad was a Marine Engineer I haven't seen his in 20 years.

[farmer58za]

If it was me, I'd do the washer (a nice thick one with a snug fit) , but I'd tack weld or braze it from the outside.
Regards
David