LCGB Forums

Hello,

My brother in law has an Italian GP200 fitted with a Mugello kit.
He’s now done about 1000 miles. What mileage do you need to
Torque down the cylinders head nuts and to what torque value.

Thanks guys.

Lee

Peoples opinions will vary on this i usually run my engines up when first built in the bike or in a jig for 2 heat cycles up to normal running temps let it completely cool down then re torque otherwise 500-1000 miles re torque

I don't know where the recomendations for re-torquing comes from or whether it is based upon any proven scientific basis.

I am not questioning the fact that some feel it a necessity, but can only state my own beliefs.

With all engines that I have ever built from the 70's, I have always omitted the cylinder head gasket as having experienced failures of the seal, reasoned that the gasket increases the chance of leakage. It has to seal on both of it's sides, thus doubling the surface area to be sealed. The gasket would have been a sacrificial compromise to allow for manufacturing tolerances which can be overcome by improving the mating surface of head to cylinder.

Even the many other engines that I have taken apart (yet never previously touched or had not been apart from the day the engine was factory assembled) have all displayed indications of leakage. Presumably that was the norm & of no significance in the case of OEM engines which must have sealed again upon expansion through heat as no indications of weakness were evident

That said, preferably any engine receiving attention by way of an upgrade should incorporate a spigot which will virtually guarantee a seal whilst having the added benefit of centralising the squish to the bore. Performed correctly, there will be no requirement for any proprietary sealant.

Spigotting is not always an option, in which case I have used Green Hermetite, grease, bathroom silicone or lately, Loctite Golden silicone.

As for torque, which is the measure by which we pre-stretch the studs, I personally use a greater figure than the 15ft/lbs stated in manuals, but I am extremely fussy about the thread quality of studs & crankcase holes. Essential to my facilities are a range of rolled thread studs, cylinder head counterboring/facing tools, high tensile nuts, extra thick hard washers, good taps & thread repair tools including Helicoils & Keenserts. Helicoils are as good as any other method if the parent material (crankcase mouth area) is fit for purpose. I have yet to see a Lambretta crankcase devoid of porosity following welding by even coded welders, which is hardly surprising. Cut a magneto housing apart & the likelihood is that there will be porosity as standard from the factory, even Innocenti. Any of us that have been passengers in a plane will have been supported by fasteners screwed into thousands of Helicoils.

The reason that the studs are torqued up is to allow for thermal expansion & contraction of the cylinder assembly. It could be argued that the amount of torque should vary if the cylinder is alloy as opposed to cast iron, but I have yet to apply that logic.

So I'm not entirely sure as to why the fasteners need re-torquing

Thanks guys will visit Mugello Facebook

I'm with WT1 here - I rarely retorque once built and pressure tested.

I also rarely use gaskets on the head and only occasionally on the base or packer and always use loctite copper silicon on both.

I agree with the posters who say they do not re-torque the head after a period of use. I never did this in my early days of scootering, probably because I did not have a torque wrench that went low enough. After reading the posts, when I returned to scootering, on the importance of doing so, I did but found no loose ones so I stopped. This theory of not retorquing is also based on years of checking heads on tractors on first services that were never loose. But this is my opinion and I respect those who think differently.

Over ten years ago, I had a Mugello 186 and also, briefly, a 200. I was having issues getting the cylinder head to seal on the version 3 186. When I came to check whether the mating services were flat, neither the head, nor barrel, were. They were torqued to 18, no more.

In my opinion experience, therefore, I would check the torque but I wouldn’t, personally, go over 18lb. Sq “.

Storkfoot wrote:Over ten years ago, I had a Mugello 186 and also, briefly, a 200. I was having issues getting the cylinder head to seal on the version 3 186. When I came to check whether the mating services were flat, neither the head, nor barrel, were. They were torqued to 18, no more.

In my opinion experience, therefore, I would check the torque but I wouldn’t, personally, go over 18lb. Sq “.

In the instance of spigotted heads to barrel, I have no doubt that I could, & probably should, reduce the torque applied, but I have been using my own trusted figure for years, & you know what they say about old dogs & new tricks

The fact that I failed to mention earlier that I apply a little Copaslip probably increases the compression of the whole assembly via stud stretch as well. However, I really do ensure that all fasteners are first class & have a stock of really thick washers that I will use, even if the counterbores in the head require deepening.

This is off topic, but re-torquing or checking of car wheel fasteners should always be done IMHO. If tyres are fitted @ a depot, check the torque values as soon as possible. Having experienced the over stretching of bolts & the results, I really cannot over emphasise the need to check. If you find them way too tight, insist upon a full replacement of OEM studs. I did & got them.

Warkton Tornado No.1 wrote:

Storkfoot wrote:Over ten years ago, I had a Mugello 186 and also, briefly, a 200. I was having issues getting the cylinder head to seal on the version 3 186. When I came to check whether the mating services were flat, neither the head, nor barrel, were. They were torqued to 18, no more.

In my opinion experience, therefore, I would check the torque but I wouldn’t, personally, go over 18lb. Sq “.

In the instance of spigotted heads to barrel, I have no doubt that I could, & probably should, reduce the torque applied, but I have been using my own trusted figure for years, & you know what they say about old dogs & new tricks

The fact that I failed to mention earlier that I apply a little Copaslip probably increases the compression of the whole assembly via stud stretch as well. However, I really do ensure that all fasteners are first class & have a stock of really thick washers that I will use, even if the counterbores in the head require deepening.

This is off topic, but re-torquing or checking of car wheel fasteners should always be done IMHO. If tyres are fitted @ a depot, check the torque values as soon as possible. Having experienced the over stretching of bolts & the results, I really cannot over emphasise the need to check. If you find them way too tight, insist upon a full replacement of OEM studs. I did & got them.

Agree with the last bit, I have watched then w**k them up with the air gun and then 'check' with a torque wrench but you don't know what it's set too.

Thanks guys for all the info ...