stainless steel - acceptable uses on Laverda's?

An interesting techie thread. I accept and respect that Paul will do it the OEM way so I?m not trying to influence anything.

Simon?s temperature expansion rates are interesting as well as Piet?s similar thoughts but it doesn?t explain one thing. The valve cover is alloy. It is soft enough to be scratched by a clumsy mechanic with a screw driver or allen key. My question is this, why would the head of a high tensile bolt/cap screw pop off instead of staying where it is and burying itself into the cover until it punches a bigger hole through? Why does the soft survive when the hard is broken? It simply doesn?t address the symptoms.

Cam?s post on crevice corrosion is interesting and I?m seeing it as a viable theory along with plain old electrolysis that I?m familiar with.

I have a broken off bolt in the engine casing on my Morini. I?ve tried to centre punch the middle and drill it out but it is hard, very very hard. I can live without it so I do. I?ll probably get it spark eroded if and when I ever pull the motor to pieces. The head was broken off as the bolt has welded itself into the casing. All before my time.

My theory is that 12.9?s were used due to lesser grade bolts welding themselves into the casing. At least a 12.9 gave you a chance to put a good tool onto it and give it some leverage. The heads of lesser bolts just sheared off. If so the issue isn?t bolt strength its electrolysis between the metals.

Be very careful using anti sieze. I?ve worked on aluminium ferries and depending on the type of alloy and the type of steel/stainless all you are doing is adding another metal into the nobility stew. Rubber grease or lanolin are good if temperature isn?t a major issue.

I rebuilt a Volvo diesel (cast block) a while back. In their recommendations they specified a coating of 50/50 tectyl 506 and white spirit for the studs. The white spirit is really just any thinner to help spread the tectyl. I only mention it as an example as it is rare to read such an instruction.

I tend to use a good moly fortified bearing grease on bolt threads in similar applications. Survives the heat and allows for easier removal down the track.

I don?t know what the answer is but shear strength of a 12.9 isn?t it.

Just my observations.

Rod

 
Yes, interesting topic. If the cam cover bolts are highly loaded when the engine gets hot, then I suspect that differing expansion rates between bolt and cover aren't the source of the problem.

The top of the cover will tent to "lift" with expansion by an amount related to its increase in temperature and the height of the cover from its mating surface with the head. The camshaft bearing cap into which the cover retaining bolt is fixed will lift with expansion relative to the same reference point (mating surface of the cover) by a somewhat lesser amount because even though the bearing block is aluminium, it is restrained by the cylinder studs that go all the way to the crankcase. The aluminium barrels and head will expand more than the cylinder studs, so the studs will actually become tighter as the engine warms up. Another way of looking at it is that it's not so much a case of the cam cover lifting upwards, as the cam bearing blocks being pulled downwards away from the cover by the increasing tension in the studs.

Buggered if I know why the factory would have chosen high-tensile M6 bolts as a solution though. It would have been easier to simply increase the bolt size. Maybe they had already made a million bearing caps with M6 inserts in them before they realised there was s problem.

It's a bit of a dodgy way to fasten a cam cover when you think about it. I'm surprised that they don't piss more oil than they actually do. Look at any Jap bike and it'll have a zillion M6 bolts all around the edge where the cover joins to the head.

Cam
 
Perhaps the reason we should use 12.9 bolts is quite simple. Someone in lets say Germany has boxes of these 12.9 bolts that are too short for any other application and he's trying to get rid :D

Only joking                                              Dave             
 
Rod, Cam,

You're both overlooking a couple of factors.

The bolt has no connection to the head or engine casing, only to the cam bearing,  Apart from the contact through the rubber gasket to the head, it "floats" above this.  Therefore, the alloy cast above the retaining nut and the alloy of the cover are the expanding bits of alloy stressing the bolt.

The 12.9 bolts do not shear, only the bolts of lesser grades.  The bolt does not damage the cover, the copper sealing washer is sacrificed.  It cannot punch a hole through the cover because this is firmly attached to the cam bearing and has no leverage to the head to be able to force off the bolt head by this means.

The cam cover bolts thread into the steel insert only, no alloy threads involved (unless you force in too-long bolts... then you really get into trouble :D).  No great chance of any form of electrolysis damage, especially as there is oil flying all over the place.

The factory used larger bolts on the racers to address the problem, which messes up the looks of the cover big-time, probably not an option for production bikes.  Seems the 12.9 bolts were the easiest fix.

The most common japanese method of fixing a cam cover these days is actually very similar.  They no longer use a myriad of bolts around the outside, usually just 4-8 bolts distributed in the same way as Laverda did.  Instead of a solid mount with copper sealing washers, they use large-headed shanked type bolts through rubber grommets.

Correctly fitted, with a new gasket when required, a Laverda cam cover is bone dry, Cam.

piet
 
12.9 High Tensile steel bolts were the solution, not the problem according to the factory. They will withstand the extra strain exerted by differential expansion.
Lets say a bolt is attached to the cam blocks - so the block is our datum point, then there is a thick layer of aluminium cover wedged below the bolt head. The bolt head is torqued to 'x' when cold against the alloy. When the aluminium cover heats up it expands faster than the bolt exerting an extra force 'y' on the bolt head because our datum hasn't moved in relation to the bolt head - the bolt and cover moved with the engine together. This extra force overwhelms the bolt and snaps it.
Sure there may be some difference in movement between outer bolts than inner, it will be small and the cover will flex.
What I was saying was that the A2 stainless screws expand at a rate closer to the aluminium so the extra force 'y' is much smaller.

The aluminium may be a lot softer than the bolt, but maybe the surface area of the soft metal is able to adsorb the force of the bolt head without deforming too much, especially if there is a washer below the head (I have fitted washers).

Alpino said:
I have a broken off bolt in the engine casing on my Morini. I?ve tried to centre punch the middle and drill it out but it is hard, very very hard. I can live without it so I do. I?ll probably get it spark eroded if and when I ever pull the motor to pieces. The head was broken off as the bolt has welded itself into the casing. All before my time.
Click to expand...
Spark Eroding is probably the way to go. I have previously drilled out hardened steel pins with cobalt drills and then diamond ones - right royal pain in the arse and expensive.


Alpino said:
I tend to use a good moly fortified bearing grease on bolt threads in similar applications. Survives the heat and allows for easier removal down the track.
Click to expand...
Moly, Nickel, Titanium greases seem to be all the rage (Moly always was). Copper Grease has faded to oblivion in some industries - except automotive.
A Gas Turbine company that I dealt with will not let copper grease anywhere near their engines.
 
I have had a stainless cam cover bolt break while out riding....first I knew about it was when my foot slipped off left footrest...oil everywhere.I changed all back from ss to the nice knurled ones from Slaters...notice Keith has nicked those and I am back to ss! Am going to change back...
Nick
 
Well, there goes my theory!

My s/s ones have been in for a few years now, but I have washers underneath (can't remember if they are copper).
You are unlucky to get a big leak with only one bolt breaking, you would have thought that the rubber gasket would still seal.
That said Keith knows what he is doing, he certainly went over my bike and changed a couple of things he wasn't happy with (like my master cylinder seals that I sobotaged with DOT 5).
 
Simon, I agree you would have thought the gasket would still seal....when you are by the roadside all everything is covered in oil,the cam cover is the last place you look...but that's wot dunnit!then you have to consider whether to ride home albeit just a few miles with what oil remains!
Anyway, back to my degree wheel and piston stop to get TDC  and reinstall the Sachse. Ignition after fixing the knackered starter clutch....
 
Well it would likely leak out of the bolt hole, not necessarily because the cover had pulled away from the head and overcome the rubber seal.
 
But no head on the bolt bearing down on the copper washer to seal it, no?
 
I digress but starter clutch works and bike starts and runs! Ticks over nicely. Clem has lent me snap on strobe so will check advance tomorrow. Bad news is my nicely newly sprayed up tank was on bench too full and has leaked and bubbled paint...Clem I will be over  shortly for Tom to look at!!What with Clem and Tom and David ( who recently made up an extended 36 mm socket to get nut off crankshaft) where would I be? Rubber ducked  without doubt :D
 
breganzane said:
You should use unplated ones then Paul.  I'll be marking you down for that at Wolfgang's next impromtu concourse.  :D
Click to expand...

Hi Steve

you have me laughing out loud yet again.......

as there are now three Laverda triples in the stable, bring Christiane as well, picture three Laverda triples howling along at full chat shoulder to shoulder to shoulder on the road down from Revelstoke to the ferry...... ;) :D

Paul LeClair
 
Sounds to me like a waisted bolt / stud would have sorted the problem much easier.
This would allow more "elastic" stretch thus compensating for the alloy expansion differential.

Julian
 
okay, how do the billet alloy cam blocks come into play then if these high tensile cam cover bolts are so essential
I have installed stacks of our billet cam blocks with no issues at all and there were quite a few billet alloy cam blocks on the market before we started making them
only started to make our own as main supplier of the CNC blocks could not keep up with the demand, waited 7 months for 5 sets, finally said stuff that, easier to make our own blocks

so what is the go with expansion rates, 12.9 rated bolts etc when using billet alloy cam blocks
I have never seen an issue and have around 30 engines running them now, none are leaking as far as I am aware and at least 8 off those engines come to our workshop on a regular basis

I don't doubt what you say in regard to the 12.9 bolts, am just curious, constantly learning about these old clunkers


 
Red,

Just observe and see what happens.  Especially on the race-thrashed engines, these would be the first to be effected.  Maybe the expansion rate of the billet alloy matches the rate of stainless bolts closely.

Reckon there won't be much of an issue during normal road use, just won't be enough heat to make an impact.  Of the many triples that have gone over my bench, I have found about 3 afflicted by broken cam cover bolts.

The people at the factory weren't the type to change things because they didn't have anything better to do, changes were usually reactions to inadequacies of some kind or another, hence the 8mm bolts in the early triple racer cam covers.  Didn't Gijs mention his woes with snapping studs on his racers?  He has re-made almost every stud in his engines from higher tensile material due to the stock items failing again and again.  Roger recalls the Team Van Dijk Zane 750 losing 2 crankcase studs during the 24 Hours of Liege at Spa, 160mm long and managing to vanish, even though there was only 20mm of free space between the crankcase and fairing.  Gijs has had both cylinder and crankcase studs fail on the triples, the cam cover bolts were converted to M8 from the start.

piet
 
After the big prang in 1984 on a diesel coated roundabout, I rebuilt the Jota 120 with as much stainless (A2 and A4) as possible due to the poor condition of all the original bolts. I live on the coast, so salty conditions everywhere. Mucho corrosion present.
The rebuild included both axles, spacers and many other parts supplied by Malcolm Cox when he was working out of his Yardley Birmingham workshop. Looking through my Jota 120 file (it makes interesting reading) both axles together cost ?28 back then.  :o I also purchased M8 and M10 stainless rod and had things like brake and gearchange connecting rods replicated as well.
I'm happy to say that after all these years I haven't had any issues with using stainless parts and will continue to do so with my future rebuilds too.

Cheers

DoC!   
 
If you use stainless steel bolts and mounted in aluminum bolts will always be the strongest, and therefore it does not matter whether it is stainless or 8.8/12.9
This also applies brake parts where the nut portion is made ​​of aluminum.
Nothing is stronger than its weakest link.
 
What you say sounds logical Koch, because aluminium is softer than steel. But it's not quite as simple as that. If it were, you'd never get steel bolts broken off in aluminium threads.

Cam
 
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