LCGB Forums

Hi Chaps,
If you have just rebuilt an engine an easy way to test for leaks is to take a cycle tube and cut it 12inches either side of the valve attach one end with a jubilee clip to inlet manifold and the other end to the exhaust u bend .pump it gently with a bicycle pump. and use a soapy water spray to check for leaks .April 2013 edition of scootering used a blood pressure kit and quoted a PSI of 5.8.On my initial post on the old forum I used two pieces of inner tube(pictured) until Scooterlammy pointed out that it would better to use a single piece as stated above , a fine example of an idea being taken up and improved upon.
Although the old forum database appears lost the ideas,fixes, pictures of rebuilds and comments are still there on individual member's computers and could be re-inputed to rebuild the database.
This is a start
Grandpa

Absolute cracking idea, have since used this twice now on 2 different engine rebuilds,so thank you Grandpa & scooterlammy.

Simple and Effective

Another successful leakdown test
Thank you grandpa

Great idea that!!
Once youve inflated to 5 psi how long does it have to hold for?
Thanks jon

jonhunter wrote:Great idea that!!
Once youve inflated to 5 psi how long does it have to hold for?
Thanks jon

I don't know how others have got on but I found that my gauge wouldn't register any pressure as the inner tube just kept inflating. I just squirted bubbles over all the joints until I could spot no more air leaking. It did reveal a massive leak from the exhaust flange/barrel.

I check with soapy water for leaks only.

I've tried a couple of different leak tests including the inner tube method but the best one I've used to date has an adapter that fits into the carb rubber, this adapter has the pressure gauge screwed directly into it, when it's under pressure it can be read at the inlet stub.
The kit uses less connections so gives fewer chances of leaks developing in the test kit, plus it pressures up easily.

Captain Pugwash wrote:I've tried a couple of different leak tests including the inner tube method but the best one I've used to date has an adapter that fits into the carb rubber, this adapter has the pressure gauge screwed directly into it, when it's under pressure it can be read at the inlet stub.
The kit uses less connections so gives fewer chances of leaks developing in the test kit, plus it pressures up easily.

Yes Mark, I think it was your post that set me searching ebay for the necessary bits to construct one using a blood pressure kit. I have the parts but not had the opportunity to test it yet.......My blood pressure is fine though

Keep putting off leak down test, but taking an engine out this weekend so I've got to motivate myself. So going to try the rubber tube method. But having no experience with mountain bikes, I note that there are different internal diameters. Now I appreciate that they will stretch, but what the best internal diameter to buy for a 30mm carb and a TS1 exhaust stub, don't want to get it too big so as to end up with the tube end leaking.

Paulnobodyimportant wrote:Keep putting off leak down test, but taking an engine out this weekend so I've got to motivate myself. So going to try the rubber tube method. But having no experience with mountain bikes, I note that there are different internal diameters. Now I appreciate that they will stretch, but what the best internal diameter to buy for a 30mm carb and a TS1 exhaust stub, don't want to get it too big so as to end up with the tube end leaking.

I picked one up from the bicycle section in Asda, I think it was 1 3/4"...they only did the one size anyway and it was an easy stretch fit on the 30 phbh manifold and both an Ancilotti u bend and a TS1 stub.

Hi
Good to see the idea is still in use and not forgotton
Grandpa

Cheers Coaster & Grandpa, I knew you come through.

Hi Grandpa.
What a cracking idea.
Stag

This is what I used,for 30mm PHBH manifold and MB BGM exhaust stub.

What's the concensus on how long it should hold pressure for.

5 minutes, half an hour?

What position should the piston be at when doing a test ? I'm sure I've read it somewhere - probably in Stickys book.

Cheers

BDC

There's a section about this in the Edition 3. Position of the piston isn't massively important because even near the top the pressure will slowly leak past the rings until it evens out both above and below the piston, however this looks like a slow leak until they balance. If the piston is at BDC (reed motor) then all the ports are open then the pressure is the same throughout. Several tuners have told me not to try to get a perfect seal, particularly on a brand new motor where the seals have yet to bed in perfectly against the crank - very slow leakage can still be acceptable.

Sticky wrote:There's a section about this in the Edition 3. Position of the piston isn't massively important because even near the top the pressure will slowly leak past the rings until it evens out both above and below the piston, however this looks like a slow leak until they balance. If the piston is at BDC (reed motor) then all the ports are open then the pressure is the same throughout. Several tuners have told me not to try to get a perfect seal, particularly on a brand new motor where the seals have yet to bed in perfectly against the crank - very slow leakage can still be acceptable.

So 5 mins with little/almost no pressure loss would be satisfactory?

Having some issues with a standard motor, and trying to go through everything with a fine tooth comb.
I want to have faith in the air leak test performed before moving onto the next suspect which is the carb...