inlet manifold gasket replacement?

[Andie]

My (regular left hand side standard) inlet manifold either came loose or I blew the gasket - and then the inlet manifold came loose... bits of gasket and screaming engine everywhere Etc. I am replacing it this weekend.

Previously I used nylocks and a washer - but i'm curious as to whether a nylock wouldn't just melt.

Would I be better with liberal grease on the gasket, a spring washer, locktite and a standard nut? or am I ok to use nylocks?
Will I need to get the barrel off to check for gasket debris? I'm rather hoping not tbh.

what might be best please?

Thank you. Andrew

[NorthernJordan]

I've never had an inlet manifold come loose. But I either use gasket sealant or grease. Grease is better if you need to work on it by road side as the gasket is less likely to split.
As for nuts, I've either used nylocks or brass nuts with both a flat washer and spring washer where possible. It's bast to use a manifold with perfectly flat points for the nuts to sit perfectly on.

[HxPaul]

I always use nylocs on the inlet manifold,it doesn't get hot enough to melt the plastic in the nyloc.I never use nylocs on the exhaust manifold because that WILL get hot enough to melt the plastic.
Make sure the thread on the inlet manifold studs reaches the plastic on the nyloc nuts.

[Tractorman]

I use silicon sealant on the inlet manifold and nylocs.

[Knowledge]

Andie,

Are you sure that the nuts came loose, or have the studs come out of the barrel?

[Andie]

Hello and thank you for the replies -

I'm working on the scoot now and have managed to get the manifold off (not an easy task with the engine still in, also I couldn't get the carb off!)




The nylocks were loose but the studs are still in the barrell and all the gasket had gone from the face, there's some crud on the RHS stud that I am cleaning off, slowly, with a toothbrush. I'm guessing maybe the gasket blew.

I'll get it back on with nylocks and spring washers - it had wavy washers on before. - just read that loctite is bad for nylocks so won't use any!

All i can think is that the carb has been on/off a dozen times lately, maybe that contributed.

Andrew

[Phil D]

Hi Andie
I think you've probably " hit the nail on the head " nylocks loose their ability to grip the thread when they are repeatedly used .
Its best to use new ones if poss.
Especially on Lambretta

[Andie]

Hi Andie
I think you've probably " hit the nail on the head " nylocks loose their ability to grip the thread when they are repeatedly used .
Its best to use new ones if poss.
Especially on Lambretta

Thanks Phil. After an evening in the kitchen I've fitted a new gasket and had a general tighten up of exhaust etc. Whilst I was at it I polished up the carb manifold mating end so the carb goes on/off smoothly with no great use of force.- should've done that before. Took her for a spin - all good.

I've noticed the gaskets, as with others I've tried, are good quality but not perfect matches, no surprise really as all the engine components are from different suppliers, remade/recast general issue etc.. I'm looking into making them myself.

[Phil D]

I remember reading an article in a scooter magazine all about gaskets.
The top engine builders make their own gaskets (probably for that reason)
The guys on this forum do a lot of miles and have masses of expertise and over the years will have found what work best for them .
Glad it's all back together .

[HxPaul]

For ease when taking the manifold off I always take out the longest stud with the manifold.If you can get a bolt as long as the stud,its best to replace the stud,use a good stud loc on the threads and a spring washer under the bolt head.Doing it this way it makes taking the manifold off while the engine is still in the frame an easy job.As for the new gaskets,its better to trim them so that they're the same size as the inlet port.By the way,wavy washers are perfectly ok instead of spring washers under the nyloc nuts because they're not as thick and they bring the nyloc nuts down the thread of the stud,you shouldn't need the spring washers because the plastic in the nut grips the stud thread.

[peejay]

hi Andie
i know you have now got the engine back together and running.
have you used an ethanol resistant gasket, this is most important.

i make my own now after an ordinary shop bought one blew out some time ago.

you can buy small pieces of various thicknesses quite cheaply.

[xenia1]

hi Andie
i know you have now got the engine back together and running.
have you used an ethanol resistant gasket, this is most important.

i make my own now after an ordinary shop bought one blew out some time ago.

you can buy small pieces of various thicknesses quite cheaply.

Peejay makes a good point. There are many materials that are not ethanol compatible, this site lists those which are and which are not. It lists aluminium but as the manifold is an alloy i doubt this would apply..


http://iqlearningsystems.com/ethanol/do ... bility.pdf

[Andie]

Thanks for the posts.

After your replies I think a longer stud, or use a bolt, on the LHS/Rear facing barrel/manifold interface would be better, as the other has plenty of room for a spring washer, flat washer and grip on the nut, but the other leaves little room for this; or maybe the manifold could be modified by grinding down on the LHS - the RHS stud tube is approx 12mm and the other side approx 30mm. Perhaps other people do this already.

The gasket doesn't match well - and this is the third I have tried (from my first re-build, having rejected a few but finding the rest the same) - all were the same shape - no offence at all to suppliers - most people, including mechanics, I have spoken to agree that specs are somewhat arbitrary. I think custom must be the way forward in this case and unsurprising for for a 60+yr old engine design.

I am assuming these are ethanol proof as I am buying them from top-shelf suppliers.

Ideally I would pay to have the barrel inlet port and manifold matched by an engineer. maybe in january when it gets salty.

This is the fit onto the manifold (a standard innocenti marked 175 manifold I have had sleeved to accomodate the jetex) - it leaves a maybe 5mm of gasket on the bottom RHS which can't be clearly seen.



I am only mentioning this as a hopefully positve comment and am not knocking the suppliers at all.

I guess one of the reasons I like lambrettas is because they are not 'one deep' technology, but it took me many hours to change that gasket! my maintainance skills are getting much better, but i'm wary of long runs until I have resolved all of these sort of issues, which I know others have sorted years ago; to break down on a £1.00 gasket is like losing a horseshoe on a joust. The old girl has had a bit of a year of it mechanically wise, most of it down to me learning on the seat.

Spending the time matching the manifold end to the carb should help a lot, it would previously take me ten minutes to get the carb off, and i did notice it was hammered on/off by others - which I'd prefer to avoid at all costs.

Thanks again for your help. This forum has sorted me out a lot. Andrew

[rossclark]

Check the gasket match on the barbell and trim to fit, then recheck on the manifold. That should tell you how to match the manifold to the inlet port.

[Raveydavey]

Check the gasket match on the barbell and trim to fit, then recheck on the manifold. That should tell you how to match the manifold to the inlet port.

+1. Assuming barbell is just predictive text for barrel.

Always work from the cylinder backwards. Matching a manifold to cylinder is just that. Gasket matches the cylinder and the manifold matches the gasket. Simples.

[dave411]

hi Andie
i know you have now got the engine back together and running.
have you used an ethanol resistant gasket, this is most important.

i make my own now after an ordinary shop bought one blew out some time ago.

you can buy small pieces of various thicknesses quite cheaply.

Peejay makes a good point. There are many materials that are not ethanol compatible, this site lists those which are and which are not. It lists aluminium but as the manifold is an alloy i doubt this would apply..


http://iqlearningsystems.com/ethanol/do ... bility.pdf

Never heard of Ethanol resistant gaskets befor???

[HxPaul]

You should use a manifold thats made for a 22mm SH/2 carb.The internal diameter of an original 175 is 20mm,the jetex carb has an internal diameter of 22mm.These manifolds can be bought from most scooter shops that sell parts for Lambretta's,they come in smallblock sizes for 125 to 175 cases or largeblock sizes for 200 and above cases.