water test method for air leaks???

[minmax89]

minmax89- maybe it is not your bearing that is leaking. you might need a new crankshaft. possibly theres a spot on the crankshaft that is not sealing with the bearing?

Oh my god lads! Seems darkslayor24 may be right!

I finally got to do a test tonight.

One engine with backplate, carb neck/pin sealed - check!

Spare piece of fuel line on carb nipple - check!

spray bottle with soapy water - check!

Wife holding camera while I thumb over the carb filter neck and exhaust header - check!


So I sprayed , then blew. The result:

Although the video is a little out of focus it clearly shows the bubbles. What it doesn't show too well (but is crystal clear in the flesh) is that the leak is actually between the inner face of the bearing and the crankshaft.

This test only confirmed what I knew from blowing it when it was dry. I could feel cold air on my hand.


I bought this engine last week from Absolute Hobbyz on Ebay. I contacted them when I thought it was the bearing and their reply was:

"...if the bearing is leaking oil/fuel.. the low speed
needle is rich. it will also leak some during break
in because of running the engine is rich..."

So now I'm about to send them evidence of the current situation.

Can anyone offer any advice as to what to do here??

Adam

 

[moe7404]

ok here i go. is the amount of leak important? when you blow into the engine the leak is going out. but when the engine is running isnt the leak going in? but i realy dont think matters.

 

[minmax89]

ok here i go. is the amount of leak important? when you blow into the engine the leak is going out. but when the engine is running isnt the leak going in? but i realy dont think matters.

I think it does matter because any air leak is inconsistent and means I can't tune the engine.

The reason I checked for leaks is 2 fold; the first being the tune/idle was not right but second was when the engine was first running in-situ my chassis was covered in fuel. Far too much in my opinion. It was very apparent where it was coming from too.

Na, in my opinion this is a bad leak.

It's just to find out whether it's the crankshaft or the bearing. A new bearing should diagnose that right? By process of elimination??

Adam

 

[MotoGod]

Yup. Might be time for new bearings. If you have a caliper...you can measure the crank and see if it's too worn or not. If the engine isn't that old....it's probably just bearings. Also if you run it too rich, the oil WILL find it's way out of the engine and that's not usually a problem during break in and such. Sometimes it goes away on it's own, but if it's long since broken in...I'd replace the bearings and see where you are....They are cheap enough.

 

[olds97_lss]

I've read that some guys actually seal that too. A very light coat of RTV on the clean crank, then push it through the bearing and let it cure.

I've never had a need to do that though and I've had many engines.

Did you notice leaks anywhere else besides the cinch bolt?

 

[moe7404]

it appears to me you cats know a lot more about this than i do.

 

[darkslayor24]

those guys above you are just professionals lol
(or at least sometimes they seem to think they are)
they are probably just rednecks from the hills and they know their stuff lol

 

[MotoGod]

<--- Yankee Redneck

 

[minmax89]

...If you have a caliper you can measure the crank and see if it's too worn or not. If the engine isn't that old it's probably just bearings...

I think I may be able to get a caliper. If I can, do you know the exact thickness the crank is supposed to be. Remember, this is the crank where all the magic 'Red Dot' work is supposed to be!

Oh and the engine is brand new!

...Also if you run it too rich, the oil WILL find it's way out of the engine...

Why is this? surely - in theory - the engine should be water tight?

...when you blow into the engine the leak is going out. But when the engine is running isn't the leak going in?...

No. It comes out. All over my truck.

 

[minmax89]

Just a conclusive (maybe!) update.

I replaced the front bearing with a Boca sealed bearing. Put it all back together and leak was still there. So, thinking the crank was undersized it was removed and sent back as replacement but before that I measured it. Crank diameter was 6.97/8mm (fluctuated between the two) at front bearing and 12.99mm at rear bearing. The callipers I used were digital and to 2 decimal places but not sure how accurate they really are.

When I got the new Crank back the other day I measured it. It turned out to be 6.98mm at the front and 12.99mm at the rear! So, either the new crank is equally 'undersized' (not likely in my opinion) or this is the diameter they're supposed to be (more likely).

I will now fit it altogether and seal it at the front.

Adam