Engine leak testing

[Andreas Piepke]

Hi All,

I put my engine case together yesterday with a new gasket and applied elastic sealant (Yamabond 4) to both case halves. I did the same to the base gaskets, installed the correct deck height and put the cylinder head back on.
Today I measured the rate of gas loss by pressurizing the engine. The pressure-time dependence is exponential, so it seems the correct description is the length of time it takes to loose half the gas pressure. Starting from 5 psi when testing, this time is now 5.8 min compared to 2.0 min before this rebuild. I didn't check for any leaks but are wondering whether anybody has a real spec on this gas tightness. Can anybody give some number I can compare to?

Now comes the thing: I put the cylinder head on, torqued it in three steps (1/3, 2/3, full value) to the values given in the manual. This worked well until I got to the last stud. When going to full torque I could feel the thread giving way! Some things are apparently not meant to be; like me finishing this engine. I will have to take the cylinder off again to fix the thread with a Helicoil insert. I only hope I'll get the base and head gaskets off without damaging them. Otherwise I'll need to order yet another set.

Cheers

Andreas

[Andreas Piepke]

I took the cylinder off again. Below you can see the thread of the right back cylinder bolt (or what remained of it). This only failed in the last assembly step.



I put a Helicoil insert in to fix this problem. Here a picture taken before breaking the tang:



I decided to put new base gasket in. I don't want to take any chances of repeating this yet again for saving $12 on the gaskets. Wish me luck that it works now.

Andreas

P.S.: The gasoline coming out of the carb when started always dissolved the black engine paint. This time I put an additional coat of clear lacquer on. Let's see whether this withstands the gasoline better.

[Andreas Piepke]

Hi All,

I put the cylinder back on:





This time I tightened the screws and bolts to only 80% of the torque in the manual. Nothing gave way. I hope the bolts will be tight enough.
This week was the Barber Vintage Festival. It was a great event, with a bunch of Pentons there racing.

Cheers

Andreas

[Andreas Piepke]

Hi All,

I've leak tested the engine again after putting the cylinder on. Does anybody have a spec on the rate of pressure loss of a properly leak tight engine. It would really help me to have some value to compare to.

Many thanks in advance

Andreas

[Andreas Piepke]

Hi Penton enthusiasts,

I don't seem to get a lot of traction with my question about an acceptable rate of pressure loss. For my engine I measured the engine pressure versus time (semi-log representation) and get:

Would you judge this to be acceptable or indicative for a gas leak that warrants further investigation? I can't state the leak rate as I don't know the gas volume.

I would greatly appreciate any guidance you might be able to give me. Obviously some numbers I could compare to would be most useful!

Cheers

Andreas

[firstturn]

So are you saying in four minutes you lost 2 to 3 pounds of pressure?

Ron Carbaugh

[Andreas Piepke]

Yes that's what my measurement is indicating. Any comment?

Andreas

[JP Morgen]

From my experience those numbers are very good to excellent.

[firstturn]

Not being there and not know how much oil was on the cylinder walls it looks good to go.

Ron Carbaugh

[tvrc18]

I always used 1 pound lost in a 5 minute period was good. Anything else and you still have a problem.
Terry

[Richard]

I think I remember that you said that the connecting rod had been changed. I was wondering if the crankshaft runout was out of limits, could that cause an air leak at the seals. Could you test for that by rotating the crankshaft while doing the leak test?

[Andreas Piepke]

That's a good suggestion. I haven't installed the left outer crank bearing yet, so I can even soap spray the seal. I've tried that before and didn't see any obvious bubbles indicating a leak. I'll try rotating the crank this weekend to see whether the measured rate of pressure rate changes when rotating the crank.

Thanks, make a post if you have an idea!

Andreas

[Andreas Piepke]

Hi Penton group,

I tried again yesterday to locate a gas leak in my engine using soapy water. I couldn't find any. I tried rotating the crank and didn't see a change in the leak rate either. I re-torqued the head to now 90% of the book value and didn't see a change in the rate of pressure drop when doing repeated measurements. Given that there also seems to be no clear spec out there for an acceptable rate of pressure loss I decided to put the engine back together now. Here you see the pressure-time dependence I have: the time constant of the drop (the fit line shown is an exponential, determined by Excel) is 7.1 min.



I also decided to install "new" fiber friction plates in the clutch:





Let's hope it'll work this time around!

Andreas

[Andreas Piepke]

Hi all,

I put my engine back together yesterday:







Let's hope it'll work well this time!

Cheers

Andreas