Topic: 6mm helicoils, 350F camchain tensioner lockbolt

[Evel E.]

Hello,

I've got a lockbolt bolt for the camchain tensioner on my CB350F.  The one that I got I think actually came off a 400F.  It's 6mm bolt with a 1 mm distance from crest to crest or whatever the 1.0 means on my metric threadpitch gauge.  The threaded part that the locknut fits on is a bit bigger, 8mm.  Does anyone have a parts book to know if this is supposed to fit a 350F too?

I knew that I didn't have any threads in the hole, but I'm looking at it and it must have been drilled out.  It's between 5/16"to 3/8" (8 or 9mm).  A 5/16" drill bit fits in a sloppy fit in the hole a 3/8" won't go.  What size threaded hole do you need for a 6mm helicoil?  I'm wondering if I can fit one.  Timecerts look a little beefier, but they're much more expensive and not available locally.

I could try buying a bigger bolt and grinding down the tip.

-Eric

[bryanj]

I think, but dont quote me, it was a 7mm drill for a 6mm helicoil so if the hole is bigger than that you will have to go keensert or something similar

[Kelvin8]

Doesn't the package for the insert tell you what size drill to use?

Kelvin

[gaijin]

I *think* a 1/4 inch drillbit works. Usually it should say on the package, if the bit isn't already included. I can check monday when I'm in the shop, I just bought one not too long ago.

[Bodi]

The part number for the 400F bolt is  90016-286-000 the 286 code indicates it's for a CB250, I am positive it's on the 350-4 as well as there are very few differences between the350 and 400  engines beyond the obvious (bore, stroke, transmission, clutch).
Your hole sounds way too big for a helicoil - the 6mm insert uses a 1/4" drill - but the hole in the block has a smooth counterbore about 4mm deep and 8mm diameter for a sealing O-ring. You describe a smooth hole that sounds drilled out, but check that you don't have the counterbore then stripped out 6mm threads below it. The bolt threads pretty much to the bottom so the entire thread depth would be cleaned out if someone torqued the bolt enough to strip it out. I have seen that bolt snapped off by rough handling of a loose motor since it sticks out when the filter housing is removed, someone may have drilled one out if that happened I suppose...
You could just use a larger bolt, I don't think there's any reason it wouldn't work. There should be enough metal around the hole to fit it.
The approach I would go for is a fully threaded insert. There's Keensert (http://www.keensert.com) and Timesert (http://www.timesert.com) and probably others. These solid stainless steel inserts are many times stronger than helicoils for any aluminum thread repair where they'll fit. I'm sure one of the various types will work for you.
An unmolested stripped out hole could be helicoiled and the O-ring counterbore would probably be usable, anything else would need some attention to avoid an oil seep around the bolt.

[Evel E.]

Hello,

I wonder if I'm going to be forced to use a larger (probably 10mm) bolt.  I was thinking about a keensert.  According to the specs I've downloaded, the 6mmx1 keenserts are 10mm deep and are installed using a 10x1.25 tap.  The 6mmx1 threaded portion of the bolt I have is 10mm deep, so it might bottom out in the keensert before it engaged on the pushbar.

I've attached a picture of my bolt.

As far as getting a keensert in the hole, I checked to make sure that I couldn't a 10x1.25tap wouldn't fit into the hole, it looks like it's the right size to thread the hole that's there.  The hole that I have is 11mm deep around the edges and 14mm deep in the canter, where I guess the pushbar is.  I've double-checked and there's not a step in the hole.  I've been riding it a little without the setscrew and it looks like there might be a little oil weeping out of the hole, but it's not gushing out like you'd think it would be.  I didn't realize that there was anything missing until I had had the bike a couple months and went to see if I could reduce the camchain clatter.   

I've tried inserting the bolt that I have (supposedly off a 400-4) and it goes in to about where the 6mm plain part begins.  Does the o-ring go around this part?  I don't think that the o-ring would seal  anything if I put it in here.  I think that the hole is too big.

Maybe a timesert will work.  Their website says it's 9.4 mm deep, but no idea on the OD of the 6mmx1 insert.

According to some stuff I've read on this site regarding 400-4's, it sounds like my horseshoe is probably seized and the setscrew isn't going to help.  I'd think that it'd be possible to free up the horseshoe pivot if I split the cases, but that seems like a lot of work for a $600 motorcycle that runs.

-Eric

The part number for the 400F bolt is  90016-286-000 the 286 code indicates it's for a CB250, I am positive it's on the 350-4 as well as there are very few differences between the350 and 400  engines beyond the obvious (bore, stroke, transmission, clutch).
Your hole sounds way too big for a helicoil - the 6mm insert uses a 1/4" drill - but the hole in the block has a smooth counterbore about 4mm deep and 8mm diameter for a sealing O-ring. You describe a smooth hole that sounds drilled out, but check that you don't have the counterbore then stripped out 6mm threads below it. The bolt threads pretty much to the bottom so the entire thread depth would be cleaned out if someone torqued the bolt enough to strip it out. I have seen that bolt snapped off by rough handling of a loose motor since it sticks out when the filter housing is removed, someone may have drilled one out if that happened I suppose...
You could just use a larger bolt, I don't think there's any reason it wouldn't work. There should be enough metal around the hole to fit it.
The approach I would go for is a fully threaded insert. There's Keensert (http://www.keensert.com) and Timesert (http://www.timesert.com) and probably others. These solid stainless steel inserts are many times stronger than helicoils for any aluminum thread repair where they'll fit. I'm sure one of the various types will work for you.
An unmolested stripped out hole could be helicoiled and the O-ring counterbore would probably be usable, anything else would need some attention to avoid an oil seep around the bolt.

[dusterdude]

evel,do you do them drawings yourself.man they look good.

[Bodi]

There's no oil pressure there, just whatever oil drips down the chain well.
Someone has obviously drilled out your hole. The O-ring goes on that smooth bit into a smooth counterbore before the threads start in the hole (the original hole, that is).
You could just leave it as is, I can't hear how loud your rattle is or see inside the motor.
If you installed the keensert flush with the outside of the engine and ground a reduced diameter on the end of a 6mm bolt to mimic the tip of the stock bolt, it should work nicely.
I would take off the cap bolt and use a nail to try tapping the adjuster rod down a bit. If it's locked solid and you can't quiet the chain at all, then leaving it as is would be a decent move until (or if ever) you decide to split the cases. If it does move I'd want to make some kind of locking bolt so an adjustment can be held in place.