HI all.

just refitted cam cover after fitting a k75 tensioner 

 on my k100 and somehow the left  middle cam cover bolt thread casting broke off

Has anyone had this happen, and apart from a different head, how did they overcome this.

There might be enough metal in the casting to drill past the end of the thread and use a longer bolt.

 or has anyone blanked the hole in the cam cover to stop oil leakage, and just relied on the other bolts to seal the cover 


I do not want to fit a different head on my bike 

So I need some advice guys

Possibly a mobile ally welder ?

Thanks on advance 

bob

There are quite a few epoxy compounds that will fix that. Devcon is a really good one I mended a crankcase on a Z900 Kawasaki that had a f***ing big hole from a broken rod.  Clean the area and remove any old thread section then put it on then drill the hole and put a helicoil in to make a good thread. It will be permanent.

Thanks Rick,

I have never used those resins and given where it is, I would not be confident of doing it properly and bits flying off whilst riding and locking the motor up

Looking at the casting, the thread length is quite short 

I wonder whether I could drill further in and final tap in and then use a different bolt ,

or find a good ally welder...and weld the broken piece back in place.

If  thought the seal would work without the pressure from the broken bolt , then I would seal the hole and try it.

 Not possible to fit a grommet either.

Thin washers and seals might work.

The joys of only having one bike again.....

I think ally welding is out because the whole casting would need pre-heating to prevent distortion. Then the repaired area would need machining flat. That means a total engine stripdown.

Now... one of the cam cap threads on my brick (no 3 exhaust) looks remarkably like that but with absolutely no room to tap any additional threads. What I did was to Threebond the inner cambox gasket to the head, then smeared Threebond on the rubber grommet. I dabbed a bit of low grip Loctite on a set screw cut exactly to the same length as the original bolt and wound it in slightly more than finger tight so that it bottomed out on the remaining two threads in the cam cap. Somewhere in the region of 30,000 miles later there's a very faint mist of oil coming out but I deserved that because I reused an old hard grommet and instead of getting a new soft one. Have another good look to see if you can get a couple of threads tapped in there because I think you have far more room for a bodge similar repair than I did.

Thanks Dai,

There is enough room in the casting to thread further in .

I will put the broken piece back in place, clamp in position and then drill and final tap as far as i dare.

I will then screw in a stud and loctite it, then remove the broken piece and use the stuff Rick suggested to recreate 

the broken piece and hope it bonds as it is supposed too.

Normal cover rubber with nut and washer behind 

Does this sound feasible.

I shall be forever listening for  Armeggedon from the top end.

Bob

use the stuff Rick suggested to recreate the broken piece and hope it bonds as it is supposed too.
It WILL bond make no mistake and the chance of it coming off and creating havoc NIL if the surface is prepared as per instructions.
Devcon has been around for 50 years and the first repairs are still repaired.

Thanks Rick
Have ordered some.
Why the casting broke is a mystery .
At least the k75 tensioner (£12.00 excluding postage from motorworks ) fitted with only having to remove the exhaust sprocket.

Use brake cleaner (https://www.ebay.co.uk/itm/Car-Bike-Motorcycle-Brake-And-Clutch-Cleaner-Aerosol-Spray-Can/362274555848) to clean the area. It degreases anything, including your hands. A pair of protective gloves is a very good idea.

Thanks Dai

Having never used this stuff, will be interesting to see how it looks when its harde

bob

Use the brake cleaner to get any residue off then using Plasticine build up the area so you can mask it off and get in with a burr and remove the remainder of the thread and rough up the area around it so the devcon sticks then build up the broken off bit and leave 24 hours between layers and 48 before working it.  You can drill tap and bash it, it wont give.
I repaired those engine cases on a nitro drag racing engine and ran it for 8 or 9 more meetings and it didn't fail. I had a gearbox explosion which is what finished it off.

Thanks Rick.
 
I guess I would prefer your suggestion to remove all the thread and fill, reshape and then drill and then helicoil 

My worry is drilling off centre to the cover hole.

perhaps  I could make a jig using the other bolt holes to keep the drill straight .

This way I can use the original bolt 

Bob

Use the cover to get the hole concentric. The cover is flat and at 90° to the axis of the hole. I realize the flat section is not directly over the fix but could be used to help.

Thanks Rick

Once I have moulded the repair, and  then as you say, use the cover as a guide to mark the position of the new 

thread .

Due to sudden family commitments, I will not be able to start the repair for a week or so but will post pics once 

I am back home

Bob

Well,

it has been a while..

Family commitments elsewhere meant very little opportunity to work on the thread repair.

Devcon F used as suggested by Rick

A week later I have now drilled and first tapped into the blind hole .

Like  a  muppet, I forgot to order a 6mm helicoil end tap , so will have to wait till tomorrow until I can tap to 

the end of the blind hole


The use of a 1/4 inch id oilite flanged bush helped to guide the drill , though had to tap by hand , but again , 
 
keeping the cam cover in situ helped.

What surprised and worried me , was how easy the Devcon F was to drill and tap.

Should be back on the road by the weekend

Bob

Well, that didnt go to plan.

The new thread was very slightly off centre , but not enough to worry about.

My mistake was instead of just using one helicoil insert, I put two in, and cut the excess off 

I can hear the groans ....

When screwing the bolt in , the second insert must have caught the edge of the first,  and forced it out against the 

wall of the repair and hey ho, it gave way.

Round two.

I could use a 6mm stud and set into position via a bush looking thru the cam cover , and then when it has set,

 remover the cover and use devcon again to mould the edge.

Domed nut and spring washer on the stud 

or.. 

drill and tap again and just use one insert....

Bob

Hi all,

Can anyone give me the measurement between  the thread centre lines  on the  two inner cam cover bolts holes .

I forgot to do this prior to starting the repair on my broken thread.  

Just need to double check prior to drilling. 


Thanks 

Bob

If I'm understanding your intent—only one cup of coffee, so far—I would consider finding that distance using the centerline measurement of the corresponding holes in the camshaft cover.

Thanks Laitch

I have measured that way, but wondered out of interest if anyone had a cam cover off at the moment .

I measured 41.4 cm 

Using a bush through the cam cover is okay, just want to double check the starting point is spot on, as I am using 

aluminium putty for the thread repair.

Do alloy heads deteriate after 30 years ?

obviously mine did.....

bob

audibob wrote:I have measured that way . . .

Yes, I now have read that you followed Rick's recommendation using the cover as a template. Your bike's camshaft cover, your own accurate measurements, strict conformance to both Devcon's surface preparation/application instructions, and also Helicoil's installation instructions, focus and patience would seem to be the best resources at this stage.

What would you do if an incoming measurement from somebody else was 2mm or .2mm different than yours?

Hi Laitch.

0.2mm okay but not 2mm



I would expect the cam cover to be designed so each bolt hole to be in perfect alignment with its thread centre,  

so, then I trust my own measurement.

I can use a flanged bush in the cover to keep the drill straight, but I have no guide for the tap, unless I make up 

a jig .

Patience, definately, especially as I have no spare bike to ride.... .

That will teach me for dithering over mikes k1100 he recently sold....



Bob

I don't think the metal has deteriorated but that there was possibly some oil or dirt in the bottom of the thread and as that does not compress it busted the side out when screwed down. Preparation is the key to getting devcon to stick well. The surface needs to be rough and perfectly clean of oil or paint. I have used the throttle body cleaner to good effect.

Okay 

I now am a fully paid up member of the " Shit for brains club"

Drilled and tapped and put helicoil in. Alignment spot on.

Torqued up and then hey ho.  bang. 

Helocoil bunched up on bolt thread and expanded against the repair wall 

Todays lesson 

Do not assume thread sizes.

Thread size is not 6mm 1.0 pitch

1.25 ?

or does anyone know if bmw used a weird pitch.

Can you get a 1.26 pitch 6mm helicoil set?

Do I need to have all of the tapped hole filled with helicoil?

At least my method to align the hole is spot on using two 1/4 inch i/d  oilite bushes , each  superglued  either 

side of the cam cover.

Then. after drilling the hole,  I put the cam cover on my pillar drill, clamped in postiton, and  tapped the bushes , 

which guided the tap perfectly with the cover in situ


If I cannot get the right pitch helicoil then I will use a 6mm 1.0 cut down bolt and use a washer and domed nut

Patience .. Patience 

Bob

6mm x 1.0mm is the standard 6mm metric thread. 1.25 is a coarse pitch and 0.8 is fine pitch. If I asked for 6mm helicoil and was given 1.25 pitch I would be real pissed off.

The cam bolt did feel very slightly looser in the helicoil when compared with the other threads

I tried several 6mm bolts into the cam cap threads, and there was slight  resistance, whereas the cover bolts go 

in easily, hence me wondering about the pitch of the thread.

I think the bolt was pushing against the helicoil and compressing it , which expanded outwards and 

the outward pressure broke the repair.

The bolt and the helicoil felt fine until applying the pressure to torque to 4.5 lb. and then it went.

I think my neighbour has a better thread gauge . will check it 


Round three....

The cam bolt does not feel as snug when screwed into a loose insert as other 6mm bolts.

I wonder what would have happened if I had used a normal 6mm bolt instead of the original.

Though looking at the pitch they seem to be the same at 1.0

I did find the drill size was 6.3 instead of 6.2 .
 
wonder if the inserts are not exactly to spec.

This was a cheaper brand repair kit.

I will pick up a draper kit and try that.

onwards and sideways....

Bob

Just throwing an idea out there.

Is there a possibility to use one of those threaded inserts that are meant for break-down furniture?  M6 X 1.0 threaded inserts are readily available in metric sizes in box stores.  There seems to be enough room to fit the extra diameter of such an insert.  The advantage I see is that these inserts have toothed exteriors into which the epoxy can grab and secure the article.  The helicoil has a somewhat smooth exterior and does not offer a means for the epoxy to purchase against an applied torque.  The threaded insert can be ground to better fit the area closest to the casting but left in its natural state on the outside where the epoxy patch will be built up. The epoxy will flow into the rough exterior and lock the insert in-place against rotational torque.

Hi Robmack
 
That was one of the options I had considered

I would like to keep things standard, but if it comes to it,

I will look at other options.

The putty does seems to go very hard, but it does drill and tap very easily..

Plus given where the repair is, on the end of a casting.  does it have the same ability as if it was in the middle of a casting.

I could drill further into the casting, there does seem to be room, then tap and helicoil and leave a stud in site,

and as  you suggest, build up the resin around it, and use a plain nut and sprung washer.

I screwed in the bolt on the repaired thread,

I could feel pressure being applied , but then it went...and just rotated.

After removing the cover, the insert had tightened around the bolt threads.

The break in the casting is exactly where the helicoil insert sat 

Before fitting the cam cover , I screwed the cover bolt fully into the insert, and felt no resistance .

I will use a draper kit tomorrow to see if it makes any difference.

I need someone with more skill than I possess to tell me what I am doing wrong

I have used helicoils many times before without any issues

bob

What is this—the installation tang still in place?

Hi Laitch.

yes it is,

in my defence, I checked the insert on the bolt and there is a 2mm gap between the tang and the end of the bolt, 

with the insert threaded to the end of the bolt shoulder. 

bob

audibob wrote:. . . in my defence . . .

Don't mind me. I'm just one of those instruction-following drones who uses a thread-gauge because he can't operate in uncertainty.   I'm trying to evolve though.

No problem Laitch

am glad of any help.

Done some reading on helicoil faults, and one thing  I did not do, was  to countersink the hole prior to fitting the 

insert.  

I fail to see how after winding the bolt in , and feeling resistance from the rubber bush, the thread then goes awol

and breaks the repair , unless there is outward pressure from the insert.

I wonder if my cheapy helicoil  kit is the problem, I will find out tomorrow when I use a draper kit.

If, after using the draper kit, the cam bolt still feels slightly loose, as it does on the normal threads , then I will 

try using a normal bolt instead.

Maybe the issue is the helcoils / inserts that are fitted from the factory .

Using standard 6mm bolts into the cam threads are tighter .

perhaps its a mismatch issue using the cam bolts on normal inserts

I will torque the bolt through a small block to 5lbs ,without the cam cover on, and see what happens.

Bob

Finally.. success

used a stud screwed in to end of hole and used two plain nuts with sprung washer to lock it.

Thread locker used .

Just need a BMW stamped rubber sleeve over the protrusion to hide the bodge...

No leaks .  

Mot next and out for a long ride.......

Been so long I may have to take a test again.

On look out for newish second bike

Thanks for all inputs 

Bob

This is an update on my post of a busted cam cover thread during 2018.

After deciding to check my valve clearances, ( long overdue) ,  I wanted to see how the thread repair 

was standing up to some abuse over 15k miles .

Since a big bang had not occurred , a check was overdue.




There is a hairline crack which I half expected . Not very deep, but would get worse over time.

I filed around the crack to stop it spreading.  

Perhaps I  might go in a little further, roughen the area and refill with the resin  and recheck again in 10k 

The one piece of advice I would give anyone when refitting the cam cover bolts is,  unless the rubbers are fairly 

recent and soft,  get new ones and do not use a torque wrench.

Finger tight, then go very touchy feely with a small spanner. You only need to stop it leaking oil...


On a different note.
Hoping to find only a couple of valves clearances out, every bugger was just below minimum...

Since she runs very well, I have got away with this for far too long... ah well.. shims away...

Cams look like new, a testament to whatever oil I decided to chuck in..

Bob

audibob wrote:Finger tight, then go very touchy feely with a small spanner. You only need to stop it leaking oil...

One-eighth of a turn with the spanner. This gives you approx 6-8ft/lbs which is all you need.

I found that I had to replace every shim as well.  Consequently, I now own a collection of the buggers.  Post what sizes you need.  I may be able to save you some money.

Thanks Brickrider, the postage might be somewhat prohibitive to the uk.

I find it odd that if you are running a minimum clearance, you have to choose between

leaving it , or re-shim and have it at the other end of the values  because  BMW and  Motoworks only 

supply shims in 0.05 mm increments, which is the min to max range of inlet and exhaust.

If one is say , 0.16 on the inlet, then you have to leave it, or re-shim and have it at 0.21  which might mean

a noisy tappet.

I have three which are " on the line", but I will re-shim them too.

Perhaps the reason is , if you check them on a regular basis the only time you need to change 

them is when they are on the minimum value,  then as the next shim is 0.05 ,  you go back to the 

max value which would be good for many miles. 

I guess you may only end up doing one or two instead the whole set.

All my exhaust gaps are around 0.023, with three inlets 0.015 and one at 0.13 and one at 0.14

This is probably the first check the bike has had in 75k, so well overdue..

Bob

Mechanics tune up....tight inlet and loose exhaust.

I am more inclined to check them and build a picture of any changes in clearances.

audibob wrote:
All my exhaust gaps are around 0.023, with three inlets 0.015 and one at 0.13 and one at 0.14

Bob

That's even more unique than a cafe racer. Can you post some pics of your five cylinder brick?

Shoot him

Sorry, tried to resist the urge to say that but didn't succeed, but couldn't stop larfing.

Note to self......

Avoid applying for the position of Motorcycle magazine proof reader  ( technical division ) 


At least one person  reads my dribble . You know who you are..

Perhaps I should ask Allen Millyard to add an extra cylinder, then I could use the leftover  shim ......

bob

G'day Bob,

Say G'day to the wife and kids for me. This thread is a good reminder that sometimes you're better off doing the bolts up looser than tighter.

daveyson wrote: This thread is a good reminder that sometimes you're better off doing the bolts up looser than tighter.

A torque wrench is a very valuable investment.  I have a 1/4" drive version from China Crap Tools(A.K.A. Harbor Freight) that is surprisingly accurate.  While it doesn't go high enough for the larger bolts and screws, it does give reasonably accurate tightening torques on the smaller more fragile fasteners on the bike.

Thanks Daveyson , and ditto to you and yours.

Point-seven-five, having bought a 1/4 inch torque wrench for the cam and  sump covers and intermediate

housing  bolts, I was more than a bit  pissed off to find the inner seal thread casting had given way.

If there was ever a big enough reason for keeping those tb,s in perfect harmony,  this is it..

Do I expect the repair to last ?, who knows.  It has certainly scrubbed off any residual value the bike has.

It would be cheaper to fit a different motor than have the casting repaired professionally.

The torque wrench now stays in the tool box for the top and bottom end covers .

 Perhaps a smart fone endoscope camera attachment will fit through the bolt hole in the cover.

The stud can be removed to give visual access to the repair,  allowing me to check it  without

removing the cover.

 Depends on the  quality of the image , but it would be very useful.

Bob

Can you get the engine to a good welder?  I have seen worse damage repaired.  I had a friend back in the 70's who raced airheads.  He had all kinds of crash damage repaired on his engines. 

Try to find a specialist who repairs tooling and molds.  They do stuff like you have all day.

Hi point-seven-five,

 The damage needs repairing correctly, but it will have to wait until early next year

I will be in a position to buy my first new bike for a very long time next spring, so whether I need/want two bikes 

will determine what I do with her.

Should I decide to keep her, I will remove the head  and get her to  a specialist you suggest.

Bob

WHAT???!!!! Of course you need more than one bike!!!!