Engine leak testing

[Andreas Piepke]

Hi All,

I am starting a new message thread on diagnosing, and hopefully fixing, a gas leak in the engine of my 1973 Penton Hare Scrambler. We exchanged already quite  number of useful messages and I thought it would be useful to have this listed under a more appropriate subject line. For the previous messages see:
http://www.pentonusa.org/forum/topic.asp?TOPIC_ID=16030&whichpage=1

As discussed previously I replaced the right hand side crank seal and gasket under the seal holder. I also did another thing: add more soap to my "soapy leak testing fluid". The small leak at the crank is indeed fixed now. However, the leak rate is similar to what I observed before: I get a half life time (time required to loose half the pressure) of about 4.3 minutes. Is there any guidance as to what leakage rate is acceptable? This is certainly not a very large leak but observable. More spraying with soapy water revealed a leak at the cylinder base which is probably responsible for the observed gas loss. If the current leak rate is too large I probably will have to take the cylinder off and the engine out of the frame. I already checked the cylinder head bolts and found them tight. I increased the torque on the Allen head bolts from 20 to 25 foot*pound; no difference. I also checked the case bolts and found them correctly torqued too. Are there any suggestions out there on how to deal with a leak at the cylinder base not requiring engine disassembly?

As usual I appreciate your practical knowledge on all things Penton!

Andreas

P.S.: The leak at the cylinder base appears to be in the middle where the two engine halves meet.

[SouthRider]

Andreas,

If you pull the jug, try coating the base gasket with a thin coating of grease before the reinstall. Sometimes works wonders!

_____________________________________________________________________________________

"We the willing, led by the unknowing, are doing the impossible, for the ungrateful. We have done so much, for so long, with so little, that we are now qualified to do almost anything, with nothing."

1972 Penton Berkshire 100
1983 Husqvarna 250 XC
2011 Jayco 31.5 RLDS
2009 Chevy 2500 HD Duramax

[Andreas Piepke]

I was trying to get around taking the cylinder off. I guess this will require removal of the engine from the frame. Do you guys use new foot and head gaskets for every cylinder removal? How long will the grease seal? Will it not simply be blown out when the engine heats up?

Cheers

Andreas

[Daniel P. McEntee]

I'm a firm believer in good ol' #2 Permatex. A thin coat on both sides of the base gasket. It's pretty sticky, and doesn't get hard. When assembling the engine, the fit of the two case halves at the cylinder base needs to be checked, especially if you have replaced one side or the other, and appropriate measures taken to even them out. Then, when dry fitting the cylinder to the bottom end, a check of the deck height dimension so you can adjust the base gasket thickness as necessary. Most vintage Japanese bikes, which were mass produced in far greater numbers, generally are pretty consistent. I have heard and read that this area needs watching and attention on KTM and other Euro brand engines. You may not need to remove the engine from the frame, unless you have a significant mis-match in the center cases. Good luck with the rest of the procedure and I'll continue to watch the thread.
  Type at you later,
   Dan McEntee

[SouthRider]

Andreas - at this point you have been fighting an engine that is not running properly for months. Pulling the top end can be done in a weekend or less. Make sure you have a second set of hands - KTM cylinders are heavy & hard to seat on the rings by yourself without someone to help steady things.

You can sometimes get away with pulling the studs to get the cylinder off in the frame (double nut them with the head nuts). On some engines you get a little more room by removing the front engine mounts & pivoting the engine downwards.

Dan is correct about setting the deck height. On a KTM engine it wasn't so much about poor castings as it is a typical example of Austrian/German precision. OEM gasket sets came with a variety of different thickness base gaskets to allow you to set the deck height precisely to factory racing specs (blueprinted),

The proper way is to torque the head to initially compress the gaskets, remove the head to confirm the height, add or remove gaskets as necessary, assemble, then run the engine, and check it again.

In reality most engines were just run after torquing once and re-checking - skipping the "run once" step. As a practical manner whenever we tore down a customers engine we would "mic" the existing gaskets (the compressed portion in the middle) to get a starting point. Deck heights were precisely set at the factory and were usually only off if a non-trained mechanic had been in there.

The grease does not seal anything - it simply makes the gasket supple so that it can conform to the jug and cases. Artificial products like permatex are not necessary unless something is scarred or damaged by an errant putty or pocket knife.

Gaskets do not necessarily need to be replaced every time if they are intact. The grease helps with finding a gasket reusable, while the other products sometimes glue the gasket down causing it to tear or stick on dis-assembly.

Last but most importantly - if you go in - make sure that you have the tiny hole in the exhaust port side of the piston for proper lubrication of the exhaust port. If this hasn't been done ask us for instructions.

_____________________________________________________________________________________

"We the willing, led by the unknowing, are doing the impossible, for the ungrateful. We have done so much, for so long, with so little, that we are now qualified to do almost anything, with nothing."

1972 Penton Berkshire 100
1983 Husqvarna 250 XC
2011 Jayco 31.5 RLDS
2009 Chevy 2500 HD Duramax

[Andreas Piepke]

Hi All,

This is great advice. I will go for that! The gaskets I used were all new. I tried to adjust the deck height but, as you indicated, skipped the middle step. I measured 165 psi compression pressure after assembly and concluded this to be good. The two crank housing halfs are original and not mix and match. I have a second head gasket but purchased only one set of base gaskets. Yes the little lubrication holes (actually two of them along the exhaust port bridge) have been drilled into the piston.
This is actually exactly the kind of advice I was hoping for, thanks for taking time to lay out the details.

Cheers

Andreas

[Andreas Piepke]

Hi All,

I leak checked all seams of the engine again and the only leak I could identify is the one at the cylinder base were the crank cases meet. I have already taken the exhaust off:



Tomorrow I'll take the cylinder off to inspect the situation a little closer. I had hoped to avoid this but, I guess, there is no other way. I also got some fiber clutch plates, I'll put these in too along with a new clutch push rod.

Hope you'll continue helping me diagnose the problem(s) on-line, cheers

Andreas

[Andreas Piepke]

Hi All,

Today I took the cylinder off my 1973 Penton Hare Scrambler. Before that I re-measured the deck height (the cylinder was pulled down by hand-tightening the four studs):



I re-set TDC for every measurement and found an average of 0.95 mm after 10 measurements. A little less than the recommended 1.1 to 1.2 mm but not dramatically so. For the next assembly I'll correct this issue. The cylinder head was properly sealed, there is no indication of any blow-by of gas. The gasket was stuck so I'll need a new one.

However, after taking the cylinder off the deeper reason for my troubles became apparent:



The crank shaft is covered in transmission fluid, there has to be a sizeable leak. I am afraid there is no other choice now but to take the engine out of the frame and split the crank case. The crank will have to come out to get at the left seal and all that good stuff. It seems I am back if not to square one but perhaps two.

Cheers

Andreas

[SouthRider]

Andreas - when you tear it down pay particular attention to the center case gasket between the crankcase & the gearbox. Its very thin in that area. it's possible that is your problem, not the seal. They seldom want to lie flat.

Get a whole gasket set, not just a seal. When you get ready to reassemble the engine put the new center case gasket in warm water for a couple minutes, then coat both sides of the gasket with a thin layer of grease while it's still wet.

This helps the gasket to lay down and stay where it is supposed to. Get the screws in loosely and keep checking the gasket as you bring the cases back together. Don't forget to put a little oil on the main bearings, and a dab of grease on the inner seal too.

As soaked as your base gaskets are they should be changed. Either mic them for thickness, or put the same combination of thicknesses as you currently have since you already have the deck height where you want it. Grease them lightly too.

Good luck - you'll get it!

_____________________________________________________________________________________

"We the willing, led by the unknowing, are doing the impossible, for the ungrateful. We have done so much, for so long, with so little, that we are now qualified to do almost anything, with nothing."

1972 Penton Berkshire 100
1983 Husqvarna 250 XC
2011 Jayco 31.5 RLDS
2009 Chevy 2500 HD Duramax

[Andreas Piepke]

Clark, thanks for your advice! I will have a good look at the center gasket after splitting the crank case and then try to assess the problem. I have another center gasket but no set of base gaskets, only those I didn't use the last time around. After splitting the case I should probably replace the left crank seal just to make sure...

Thanks again

Andreas

[Andreas Piepke]

Hi All,

Unfortunately I had no time to work much on my 1973 Penton Hare Scrambler lately. If you look through this post you'll see the problem I have: my rebuilt engine doesn't work right. After all kinds of things tried out I believe the real problem has been identified: transmission fluid in the crank case. It was pointed out that this could be due to an improperly installed center case gasket. That would be great because it is relatively easy to fix. Last week I took the engine out of the frame again and split the cases. I took photos of the center gasket and the sealing surface:







I can't see anything wrong with the center gasket or the case surfaces. I am afraid I have to dig even deeper now, remove the crank and replace the left crank seal. At this point I am back to where I was a year ago:



As always your insights and ideas are welcome!

Cheers

Andreas

[Daniel P. McEntee]

Just keep plugging away at it Andreas. You may be experiencing the problems but are doing a good job of trying to pin point the problem. The threads have been most informative and instructional with great photos. others should and will learn from this experience.
   Good luck the rest of the way,
   Dan McEntee

[JP Morgen]

I hate to be the possible bearer of bad news, but on the early black case 250 engines, the right hand center engine cases sometime crack near the right rear cylinder stud area, and where the engine strut attaches. The silver engine cases are much thicker in this area.

[JP Morgen]

In your photo showing the piston, and with the studs removed I see a crack emanating from where the notch for the ignition wires is in the case! Good luck!

[Rain Man]

Good eye JP, I have a 4" magnifying glass for finding those hairline cracks.
 Nice Norton Andreas, what year?

Raymond
 Down East Pentons