Topic: Stripped Threads - Ruined Afternoon

[spmc]

WAS having a grand old time putting the top end back together, paying special attention to every little leak possibility along the way when out of nowhere, one of my cam tower bolts stripped the threads. Ughhhhhh.

Is there a worse feeling than a bolt continuing to turn when you know if should probably be stopping?

Anyways after doing some poking around here I figured my best bet was to do what some people have said/done and re-tapped it at 1/4".

Now just want to make sure I didn't do anything dodgy here. I'm embarrassed as hell to have a hardware store bolt in my engine now but just wanted to make sure I picked the right one. Went with the 1/4"- 20, cut to the same size as OEM, and added a washer as the OEM bolts have a bit of a flange head. Grade 5, torqued down to 7 ft/lbs...

Picture attached of my hack job. Good to go or did I overlook something?

[rluser]

I am coming at this from complete ignorance of this motor, but I do not like this solution.  It appears that you are relying on an edge of a washer of unknown metalurgy to contain the cam that will certainly hammer that washer.  I would at least attempt to spread the load across the entire flat surface of the retaining cap with some sort of bushing (or a much smaller washer that fits snugly).

[WideAWAKE]

WAS having a grand old time putting the top end back together, paying special attention to every little leak possibility along the way when out of nowhere, one of my cam tower bolts stripped the threads. Ughhhhhh.

Is there a worse feeling than a bolt continuing to turn when you know if should probably be stopping?

Anyways after doing some poking around here I figured my best bet was to do what some people have said/done and re-tapped it at 1/4".

Now just want to make sure I didn't do anything dodgy here. I'm embarrassed as hell to have a hardware store bolt in my engine now but just wanted to make sure I picked the right one. Went with the 1/4"- 20, cut to the same size as OEM, and added a washer as the OEM bolts have a bit of a flange head. Grade 5, torqued down to 7 ft/lbs...

Picture attached of my hack job. Good to go or did I overlook something?

When I rebuilt my K0 - it had 4or5 stripped threads in the head that had to be fixed.

I ran helicoils. No problems.

Don’t like the idea of sticking a bolt in there.

[spmc]

Call it a momentary lapse in clarity in my hurried attempt to get the bike back together and ride in this glorious weather we've been having.

Anyway, the bolts already removed after taking a much needed break, and doing a little more research and learning about bolt grades and metals. Didn't know what I didn't know!

Will be doing my first helicoil for sure.

[PeWe]

Thread inserts work well. That with Honda stock bolts. The cam holder bolts are forged with slim heads.

All my ported heads have thread inserts for all cam holder bolts and studs. Plus lots of cover threads.

I carefully tighten them anyway, 9Nm, not more.
Max 7.5Nm for covers.

Cam look damaged where tacho gear has contact.

[Phoenix]

In the same situation.  Had it all buttoned down and torqued until I got to the stud on the left end.  It spins.  Took it all apart and am having a hard time drilling it out with a 1/4" bit to set up for a heli-coil.  Even used a cobalt bit, but no go.  I'm sitting here trying to figure what to do next.

[PeWe]

There are cheap helicoil type kits with correct drill, tap, inserts and mounting tool. $25US here for an M6 kit with 25 inserts.

Snap off the bottom part the insert tool grip can sometimes be a problem when not snapping off completely where it should, a small part left blocking the bolt.

I prefer time-serts that unfortunately cost much more.

[nickfarrowdesign]

Oh man I feel your pain! Helicoil is your friend, just get the right size insert kit and you'll be good.

Just this afternoon I had a similar gut sickener with an oil pump mounting bolt. It turns out that it was too short and should have been a 36mm instead of a 28 and stripped the bottom of alloy casing thread, luckily I think I have enough good thread left to get the right size bolt to grab decently 🙄

[spmc]

Haha we've all been there it seems!

Gotta look at the silver lining I guess, getting really good at getting the cam chain off and on the sprocket 

[spmc]

Cam look damaged where tacho gear has contact.

And good eye but that's just a piece of floof or something, definitely looks like a chipped edge in the picture though.

[Rosinante]

All these stories of stripped threads where torque specs are next to nothing.  I assume somebody, like a previous owner, must have ignored specs.  In any case, it's enough to scare me.

[HondaMan]

So far, I have Helicoiled 4 bolt-holes in a K2 head I've installed on an otherwise-rebuilt engine. I have 2 more to go: each time I've gone to the next step in assembling this top end I have found where someone very crudely bashed his way thru here before, just to install a CX-1 cam. He even went so far as to drill thru the bottom of the head for the #2 bearing cap bolt after stripping all the threads, installing a crooked 6mm insert that ruined the bolt he then cranked in (hard) to make it assemble. He also had pulled all 4 of the bearing studs and reinstalled them without sealant, so the whole head looked like it was in an oil bath when it first arrived here.

...some people's kids...

[Bodi]

"All these stories of stripped threads where torque specs are next to nothing.  I assume somebody, like a previous owner, must have ignored specs.  In any case, it's enough to scare me."
Even the spec torque can strip in the case alloy in an engine disassembled for the first time. For the valvegear top on my 400 several have been helicoiled although my experience with helicoils is not so great, I've used thinserts on two of the ones with limited metal around the holes and they've been excellent. I go by feel now, using a good torque wrench I have stripped a few ... using the correct bolt length. It's easy to strip the top few threads if the wrong (too short) bolt is used and there are several lengths in it that don't seem too different. I have kept track of the original bolts since I first took the cover off by sticking them in a piece of cardboard in their positions. After a few decades of doing this I have a pretty good feel for when a bolt is tight enough but not about to pull threads out of the Honda alloy. I don't trust the "official" torque spec from the bike's service manual or common service manual for the 6mm ones into alloy.

[HondaMan]

I don't trust the "official" torque spec from the bike's service manual or common service manual for the 6mm ones into alloy.

Yeah, there is some error in the manuals (even the factory versions) where Honda used less threads than normal for production reasons and didn't mention it: the most-common one is the center 4 bolts on the cam bearings/rocker towers of the CB750K0-K2 where only 5-7 threads exist in the holes, far less than the old JIS standard required for the bolt size. They are the same 6mm flange bolts found elsewhere (90-100 in-lb torque) but must only be set to 30 in-lbs lest those threads die, young (most come to me pre-stripped). They were put there merely to hold the cam bearings down while the head moved between assembly stations, and to hold the wasp-waisted rocker shafts in one place. These 'feature' bolts appear in several of the SOHC4 top ends, but Honda got smarter by about 1973 or so and quit doing this...

[PeWe]

It is Honda's fault why cam bolt threads in head gives up.
Honda CB750 shop manual say:
6.5-9.4ft lbs.
8.81-12.74 Nm.
WOW!!

If they should have written 6.64 ft lbs (9 Nm), not more, no failures for those who followed the manual.
The short threaded holes, max 5.9 ft lbs (8Nm).

I have noticed that my K1 and K2 heads have rather bad aluminium with much pores, not as a later K6 head or 392 head that are better.

[HondaMan]

It is Honda's fault why cam bolt threads in head gives up.
Honda CB750 shop manual say:
6.5-9.4ft lbs.
8.81-12.74 Nm.
WOW!!

If they should have written 6.64 ft lbs (9 Nm), not more, no failures for those who followed the manual.
The short threaded holes, max 5.9 ft lbs (8Nm).

I have noticed that my K1 and K2 heads have rather bad aluminium with much pores, not as a later K6 head or 392 head that are better.

Yeah, that's quite a spread of torque values! I think the author looked at the numbers for those cam bearing retainers' torque (6 ft-lb) and the normal for 6mm x 1mm (9.4 ft-lbs) and just typed that up.

[Don R]

In the same situation.  Had it all buttoned down and torqued until I got to the stud on the left end.  It spins.  Took it all apart and am having a hard time drilling it out with a 1/4" bit to set up for a heli-coil.  Even used a cobalt bit, but no go.  I'm sitting here trying to figure what to do next.

    When I had one that laughed at my drill there was already a helicoil in there. Get a good light and look, the head is soft aluminum.

[MRieck]

9.4 lbs for a 6mm in crap aluminum....that's funny. I just had to put a Helicoil in a R6 cam cap hole...those call for 7.4 lbs....which is to much IMO.
Putting Helicoils in a blind, doweled hole is a PITA ...you have to be patient and have the right tools

[willbird]

The hot trick would be to thread mill starting to the bottom and milling upwards :-).

I do miss the days when I ran a 3 axis CNC milling machine and could use the machine and tooling on my own time to do personal projects :-).

Bill

[PeWe]

Not fun when cam stud just coming up when tighten or bolt suddenly go easier.
I usually say to my self, good it happened now and not later.
I always look carefully to head aluminium around stud for a small radius that can be seen when thread had started to give up.

The cyl 2-3 cam studs threads trickier to fix with engine in bike, frame kit.

Or the threads for bolts where a dowel pin sits.

Big-sert not possible when hole must be tight for the dowel pin that ensure cam holder to align correctly. So time-sert must sit good.

My K2 head had several bad helicoils I could replace with time-serts. A few bigger ones too.

Holes all the way too so JB Weld to repair the bottoms.
Used a very small (half pea size) quick clay version for lowest part of bottom, a thin layer of 24hours better JB weld over it.

Time-sert went in before final cure of JB Weld.
Test assembly with cam holder and correct bolt to feel if some JB weld had to be removed before hardened. Bolt pressed in a little was enough.

[HondaMan]

[Holes all the way too so JB Weld to repair the bottoms.
Used a very small (half pea size) quick clay version for lowest part of bottom, a thin layer of 24hours better JB weld over it.

Time-sert went in before final cure of JB Weld.
Test assembly with cam holder and correct bolt to feel if some JB weld had to be removed before hardened. Bolt pressed in a little was enough.

[/quote]

I'm trying something like that, too. With the bottom of the hole broken out, I can only reach the area with the tip of my smallest finger, trying to dab in some JB Weld to push it up inside the hole. I hope it works!

I'm thinking of maybe machining bevels into the bottom of the cam bearing housings where these bolts pass thru, and then adding some O-rings into those new recesses when placing the bearings. Gotta figure out what size O-ring could work: I think if it were 5.9mm x 0.5mm it would fit nicely and seal the hole?

[PeWe]

I checked my old photos with notes in my K2 engine build thread. Later turned to a bike thread not yet done, slow going.
I have used that ported head on my K6 though.

I could reach the too deep hole from nearby rubber coin hole. I think I put a finger blocking hole from "outside" inside head from that hole while pressing in JB Weld from top of the M6 ruined hole.

First very little 2k clay that keep the thin 24 hours JB Weld in place

I did wait until it hardened, did the thread insert after.
I think that hole was big using a self threading insert.