Head keeps blowing - advice please

[Knowledge]

Torque wrench Paul? You're just showing off now, you and your fancy tools.

[Storkfoot]

Torque wrench Paul? You're just showing off now, you and your fancy tools.

I still do the flywheel by "feel" though

[Warkton Tornado No.1]

Just trying to get my head round the modified stud WT1 wont an ordinary stud have more thread area and bottom out the same but be stronger

Bottoming out studs work well because there is a large matching surface area in the blind tapped hole for the stud to abut against.

Some engineers use ball bearings beneath the stud to achieve something similar, but not as good.

Obviously, for anybody determined enough to wind a stud in with a piece of scaffold tube (not Lambretta!) on a socket bar could strip the thread no matter what! That's why torque wrenches exist (ahem!) & many automotive instructions say to torque up a wheel bearing to a known figure & then go, say, 45° more....

Perhaps the enclosed image might explain itself better than my half-arsed attempts

Bottoming out stud.JPG

[Phil D]

The photo is exactly what I had in mind but I guess I'll just have to trust your engineering expertise it just doesn't feel right because all I see is missing threads on the ends of the studs.
Just glad I run a low power engine!

[coaster]

..... The factory recommendation on tightening the nuts was to get them all tightened down in a relevant order until they were all just biting, and then turn them all by a quarter turn (again in a pre-described order) and then go round again with another quarter turn again.
......

............... My Dad, who fixed planes in the war, taught me something very similar which I still do to this day on hubs, gearbox endplate and loads of other things.

Funnily enough, the torque wrench was invented for tightening aircraft engine big end cap bolts as mismatches in torque setting were causing catastrophic engine failures...or so I read somewhere.

Although owning 2 torque wrenches, I only use them on the flywheel and head studs, everything else is done by 'feel' using a similar method as mentioned above

[Warkton Tornado No.1]

Post by Phil D » Mon Nov 21, 2016 11:03 pm

The photo is exactly what I had in mind but I guess I'll just have to trust your engineering expertise it just doesn't feel right because all I see is missing threads on the ends of the studs.
Just glad I run a low power engine!

Last attempt, honest! Before we get: (not from you, Phil. It will be A N Other that will take exception...)

Dummy.JPG

Right.

Forget using Loctite Studlock with this kind of stud, as that would defeat the object. (The design of the stud should make any other chemical locking unnecessary)

Bottoming out of the type as I should explain, allows the full hole depth to be exploited whilst still allowing a little twist of the stud itself without loosening. So, it allows the creep inevitable as the stud is stretched during the head tightening process without it coming loose.

Now, the rule of thumb for maximum thread strength of the tapped hole for aluminium, zinc or plastics recommends the thread engagement should be at least twice the Nominal Diameter of the thread.

Even though that probably doesn’t necessarily apply to brittle castings & you allow 2-1/2 x the Nominal Diameter of the thread that still only means 20 mm depth of thread engagement.

Therefore, as the likes of Cosworth etc have clearly shown a preference for, an extended plain portion allows proper bottoming out. There is quite a large, conical area that I can’t be bothered to calculate...

How else could bottoming out be achieved unless you go to the time & trouble of having a flat bottomed drill? That's a rhetorical question, BTW!

I hope this helps because I don't think any of us thus far are trying to score points. I'm just trying to explain 'another way' as I have so often with open-minded, consenting females

[Adam_Winstone]

Funnily enough, I bought my torque wrenches (both of them) specifically for doing rear hub nuts.

The very first time that I used one, after years of not having an issue, was prior to Euro Lambretta in Ireland (one before last... 199?) as I wanted to take no risks as I had my 'good lady' on the back. Well, the hub stayed on the layshaft but the repeated hitting of various sized potholes put a massive crack through the hub and rim, with just the final few mm lip at rim edge being the only thing keeping it together! I was lucky enough to buy a hub on the first evening but all stall sold out the next day!!!

With a snapped layshaft on the way to Austria also, I'm not sure that the torque wrench use has actually done me many favours?! Nah, I'd still use one... every time!... but it does make me wonder when I am more safety conscious than many.

I also thought that fitting good tyres and tubes to good rims and keeping an eye on tyre pressure was all that was necessary to avoid blowouts... and I was proven wrong about that too!

Someone remind me again why we persevere with these old shopping bikes?!

Adam

[Phil D]

Thanks WT1 for taking the time to explain it .
Just seems a shame companies go to such a trouble to make all other high end components like cranks / cylinders / heads etc but the cylinder studs seem to be overlooked .

In the photo you used cosworth were proud enough to put their name on it .
Sorry if I've pi55ed any one off just wanted to understand .

[Knowledge]

The best studs I found were Suzuki TS185 items. Proper quality.

Meanwhile, back at the coal face, I have made progress.

Some high winds closed the Orwell Bridge today, so I couldn't get to the office. With my laptop in the office, I'd decided to go down the workshop instead. They owe me a morning off, surely.

With the Three bond repairs cured, I put some air back into the cylinder. The leaks I had tackled with the Three bond were all good but I could hear that there was still air leaking from the cylinder. I used the stethoscope that came with my cheap blood pressure gauge to isolate where the hissing was coming from (surprisingly effective) and then put some bubble solution in the right place. Yes, a leak from an inaccessible place where the reed manifold had been welded to the barrel.

I decided that I could ease-out the reed block and put some epoxy glue inside the inlet manifold, but having got that nicely sealed up, I decided to tackle it from the outside. I was able to get the epoxy glue to run down a seam to where I suspected the leak was emanating and waited for it to cure. Even if the epoxy burns off, at least I know where the problem is located and I have an alternative solution to the leak.

To my delight, the test was very good and the engine looks fit to go back in again. However, as I sit here typing this, I wonder if I should have had the piston at BDC before starting the leak-down test? The air is entering the cylinder via the exhaust port.....

I need to check where the piston is sitting in the barrel, and perhaps repeat the test.

[Warkton Tornado No.1]

Post by Knowledge » Tue Nov 22, 2016 1:54 pm

The best studs I found were Suzuki TS185 items. Proper quality.

Meanwhile, back at the coal face, I have made progress.

Some high winds closed the Orwell Bridge today, so I couldn't get to the office. With my laptop in the office, I'd decided to go down the workshop instead. They owe me a morning off, surely.

With the Three bond repairs cured, I put some air back into the cylinder. The leaks I had tackled with the Three bond were all good but I could hear that there was still air leaking from the cylinder. I used the stethoscope that came with my cheap blood pressure gauge to isolate where the hissing was coming from (surprisingly effective) and then put some bubble solution in the right place. Yes, a leak from an inaccessible place where the reed manifold had been welded to the barrel.

I decided that I could ease-out the reed block and put some epoxy glue inside the inlet manifold, but having got that nicely sealed up, I decided to tackle it from the outside. I was able to get the epoxy glue to run down a seam to where I suspected the leak was emanating and waited for it to cure. Even if the epoxy burns off, at least I know where the problem is located and I have an alternative solution to the leak.

To my delight, the test was very good and the engine looks fit to go back in again. However, as I sit here typing this, I wonder if I should have had the piston at BDC before starting the leak-down test? The air is entering the cylinder via the exhaust port.....

I need to check where the piston is sitting in the barrel, and perhaps repeat the test.

I really hope those alloy nuts have been left out of the assembly as part of the process of elimination....

[johnnyXS]

[

Funnily enough, the torque wrench was invented for tightening aircraft engine big end cap bolts as mismatches in torque setting were causing catastrophic engine failures...or so I read somewhere.

Although owning 2 torque wrenches, I only use them on the flywheel and head studs, everything else is done by 'feel' using a similar method as mentioned above

same here . I have used for want of a better word 'feel' for 50+ years and I have never had a single failure or bolt shear that I can remember although I too have had a couple of torque wrenches for the past 2x decades
I have however seen many failures due to people using torque wrenches ...either due to using the wrong settings or not having a quality torque wrench that has been calibrated correctly.

The problem with using a torque wrench on small fixings or alloy components is the abscence of 'feel' it is difficult to feel when you are over-tightening a fixing. There is a tendancy to just keep tightening a fixing even when it feels to much force is being applied ,because the torque setting has not been reached. There is the risk that A click can then take the place of trust in ones gut feeling and commonsense

[Knowledge]

I really hope those alloy nuts have been left out of the assembly as part of the process of elimination....

The Ali nuts are still there. I have not had reason to suspect that they were the cause of the head issue. I am confident that the problem was loose barrel stands, rather than loose head nuts. Indeed, when I undid the head nuts, three of the studs came out with the Ali nuts still attached. As I said previously, the studs were not fully home in the casing, but they are now.

The nuts are ali and the casings are ali. There is ali at both ends. I am not about the replace the casing with ones made of steel in order to address an unfounded issue with the metal that the studs screw into. If the ali nuts are found to be at fault next time, then I will (and should) apologise to all the ali-nut doubters who have contributed to this thread ("thread" eh? Get it?)

Anyway, I did pop down the workshop and identified that the piston was at BDC when I did the leak-down test. Phew. Shortly, I will be back down there nailing the engine back into the frame.

Pass me the lump hammer.

[Warkton Tornado No.1]

Post by Knowledge » Tue Nov 22, 2016 8:25 pm

Warkton Tornado No.1 wrote:
I really hope those alloy nuts have been left out of the assembly as part of the process of elimination....


The Ali nuts are still there. I have not had reason to suspect that they were the cause of the head issue. I am confident that the problem was loose barrel stands, rather than loose head nuts. Indeed, when I undid the head nuts, three of the studs came out with the Ali nuts still attached. As I said previously, the studs were not fully home in the casing, but they are now.

The nuts are ali and the casings are ali. There is ali at both ends. I am not about the replace the casing with ones made of steel in order to address an unfounded issue with the metal that the studs screw into. If the ali nuts are found to be at fault next time, then I will (and should) apologise to all the ali-nut doubters who have contributed to this thread ("thread" eh? Get it?)

Hmmm. You can't say I didn't try.

I suggest that anybody else that thinks steel & alloy nuts can do the same job type:

"aluminium nuts coming loose"

into a search engine.

There is a massive problem with wheel lug nuts (made of aluminium alloy) coming loose.

The only reason there is no mention of cylinder head nuts (made of aluminium alloy) coming loose is that it appears that nobody else uses them.

[Knowledge]

Meanwhile, back in the workshop, the engine lives. She sounds alright, but she needs a good thrashing up the A12.

A notable tuner has been monitoring this thread from afar, and he has suggested that during the leak-down test, you should rotate the crank. This can indicate if the crank is twisted, as the seal lip can be lifted by an out-of-alignment crank, causing a leak.

Clever advice.

[Knowledge]

Time to resurrect this thread, as the situation has not improved. Since the last instalment, I have had an issue with the head, but I have purchased a new tool. Here is the story.

In November, I popped down to see a club member based at Mersea, and the scooter ran OK on the way there, but nipped up on the way home, which surprised me. At Christmas, I had cause to try to get the scooter running but it was a git to start. As soon as it did, it was obvious that the head was blowing again. I stripped the top-end and there was evidence that the head had been blowing, and the piston and bore needed a tidy after the seizure.

I used my flat-plate to check both the head and the barrel for trueness and both appeared fine. On closer inspection, I noticed that the steel liner in the SR barrel was a little proud of the surrounding ali. It took a good hour to grind it all flat, but I thought this was good thing to find as it meant that the head would have struggled to seal against the small width of the steel, when it should have sealed across the whole gasket face of the top of the cylinder. I asked Harry Barlow about this when I was visiting him to collect my new engine, and he suggested that a gasket would be useful for taking-up any imperfections. Unfortunately, I don't have any leeway in the gasket faces to allow this to happen. Indeed, if I had room, I might prefer to use a small block head from Robbospeed, but these all need to be let into the top of the barrel. I cleaned up the studs and ali nuts, and re-threaded the them as they were a bit under-cut and biting on the thread too hard (hence, pulling out the barrel studs when I undid them). I tightened it all up using my newly acquired torque wrench.

When it was all back together I leak tested it. All OK, so I ran it into Colchester and back and all was fine.

Roll on a couple of weeks (or was it months?) and I tried to start it again and the damn head is blowing again. This scooter is running only once between head-blowing incidents.

Now I am sure some people will not want to contribute to this thread again until I dispose of the ali nuts, but I will check them this weekend and see if they can be blamed for the problem. Meanwhile, I have acquired a centre-squish cylinder head which I will be machining to give me the 65mm diameter, but with sufficient clearance to run an ali head gasket.

Does anyone anneal their cylinder head gaskets?

[Warkton Tornado No.1]

Now I am sure some people will not want to contribute to this thread again until I dispose of the ali nuts, but I will check them this weekend and see if they can be blamed for the problem.

You’re not wrong in saying that, but....not before I suggest that elimination of the alloy nuts would prove their worth.

Were you to rebuild again, again, without them & the seal failed again, then you @ least can believe it wasn’t their fault....

[Adam_Winstone]

Yep, please bin the alloy nuts and use some decent flat washers + chunky split spring washers. Whilst some will argue that you should not use flats and split springs in combination, please try this as one of your continuing build, blow, strip, rebuild, blow, strip, etc. cycle so that you can eliminate my suggestion too? Starting with 2 flat surfaces, a tiny amount of silicon sealant (anything as this should be microns only when assembled between the 2 flat faces), decent flats, chunks splits (as per Vespa wheel rims) and some decent original type head nuts (not soft pig iron of some aftermarket fixings).

In doing a quick internet search to try to determine a steel / iron grade for head nuts, I did chance upon a page all about stud stretch, under running temps, which to me illustrates why decent chunky splits work so well as they keep sufficient pressure on both nut and stud to stop the nut from loosening when the stud stretches as it gets warm. Without this spring pressure the nut has the opportunity to come slightly looser each time the engine heat cycles, explaining why people suggest that you need to then part strip the motor at low mileage to re-torque the head nuts. Personally, I think that's a balls-ache and I like to build it once, as described above, and then not need to do anything again for many thousands of miles!

Each to their own and plenty of debate to be had, if that's what you fancy (not me!), but please just try this once in your repeated build, blow and strip cycle... if to do nothing more that to prove me wrong!

Best of luck with it Knowledge (M),

Adam

PS - I have had similar issues once when the threads in the casing were weak and about to give out, allowing the stud to work loose at the bottom first but then showing as the nuts coming loose at the top.

[dickie]

Why not nord-locks?

I used them on my gt186 and was slightly nervous that heat cycles might defeat their 'cam' principle.

However, I've stripped the top end twice since fitting them and I'm now confident that they're good for this application.

[Warkton Tornado No.1]

Does anyone anneal their cylinder head gaskets?

BTW. I ‘anneal‘ all of the standard, ‘sandwich filling’ type head gaskets that come into my possession.

It is done by a process of ageing. By slinging them, unused, into a corner of the garage, they will, one day, become of use as some kind of curiosity.

If you consider head gaskets used in the karting & motorcycle engines, they are generally constrained within a recess or fit on the outside of a spigot, thereby adding mechanical strength & a simple labyrinth seal.


As for washers, the thicker & harder the material the better. It may be necessary to enlarge the CH counterbores to use them, but it is worth it IMO.

Currently I use stainless (A4) extra thick plain washers that are 4 mm thick.

I believe that spring washers should not be used but my opinion is based on experience & what little knowledge I may have acquired. I doubt that spring washers would contribute to the failures that you have encountered.

[Adam_Winstone]

^... I totally agree that the benefit of forums is for others to benefit from the experience of those that have faced these situations before. No point in reinventing the wheel every time.

Quoting what works for you is the best way of passing on good information. What works for one may not be the first choice of another.

My experience is what shapes my responses too.

Adam