Jackpiner bore

[Auto5guy]

Well tonight I finally got the barrel off my 72 piner project bike.  It seems that before somebody let it sit exposed to the elements and let the barrel the crankcase and the transmission fill with water they had seized it quite severely.  

I had thought that it was just rust on the rings holding the piston in place.  I soaked the barrel with penetrating oil for a couple of weeks and even used heat from a propane torch to no avail.  I finally had to drive the piston out with a hammer and a big brass punch.  The rust pits from the rings aren't to bad but the bore is coated in aluminum. The piston has that scored melted look to it.  I went after the bore with some scotch bright and it looks like it might be okay.

I need someone to do some metric conversion for me.  My calipers are in inches not metric.  I measured the bore between the skirt extensions on the bottom of the barrel.  It measures 2.503.  What is the metric conversion?  Is this in or out of spec for original bore?
Thanks
Matthew


WARNING: The Surgeon General has determined that castor smoke can be hazardous to your health.  It is highly addictive and causes delusions of grandeur.

[tomale]

Matt, I have a set of calipers that reads both metric as well as ASA. It has a digital read out and when you set it up for one you can convert to the other by the simple push of a button. yours reads out at 63.56 mm
I do not have my parts manaul in front of me so I am not sure about whether that is standard bore or not.

I was working on a bike that had the same problem and I was told that the way to get rid of the aluminum is to use Muric acid.. it will soften the stuff up so that it can be scrape out. The guy that told me that is the service manager of a bike shop and he is a friend so it is worth looking at if there is too much to be cleaned with a scotch pad. I would think that you would not want to just pour it in there. Maybe an eye dropper or something would work better.. just do not use it for anything else after that...

Thom Green,Still crazy after all these years!
76' 250 MC5 (orginal owner)
78' 400 MC5

[OUCWBOY]

Matthew,
There is some good news out of this. That converts to 63.5+ mm which is the std bore.
Good Luck!

Donny Smith

[wildman]

Muratic acid on a cloth applied to the aluminum smeared on the cyl. wall will bubble and stink but will dissolve the smear and not affect the iron at all. Get as much off as you can then lightly hone the cyl. Only after this can you boregage the cyl. and see if an oversize is needed. However, if you need a new piston anyway, you may be better off getting an oversize and starting with a fresh round hole. Muratic acid is used in swimming pools and is easy to find but usually comes in a gallon jug.
I'm doing a jackpiner now that was full of water and the cases were a mess. I actually got another set of cases that were not as bad but still needed welding around the crank to repair corrosion that almost ate through. I guess I will JB Weld some of the minor pitting. Good luck, hope this helps. Wildman

1975 250 Cross Country, 1974 175 Jackpiner, 1975 125

[DKWRACER]

Wildman et al. Kip Kern gave me a hot tip awhile back and he uses Red Glyptol to seal the magnesium in areas where there is h20 damage, I think he media blasted and then repaired large spots with Devcon epoxy or JB weld then gave the whole area a few coats of Red Glyptol...The stuff is amazing!!!! I have some if you need...
Tom Brosius

[john durrill]

Matthew,
 we use feeler gauges between the piston and the cylinder to get clearace measurements. 90 degrees from the wrist pin hole and at the bottom of the piston is the place to slide it in. the intake side of the bore at the intake port is where the most wear occures usually. the muratic acid workes great to get rid of the aluninum stuck to the cylinder , just keep it off of the aluminum parts of the cylinder. in the front of your Penton shop manual there is a table of metric to inch conversions that is a gerat help when working on your Penton.
 Hope this helps,
 John D.

[Auto5guy]

Thanks for all of the helpful responses guys.

I think I'll take Wildmans advice and bore it since it needs a new piston anyway.  After having my Harescrambler self-destruct its Carl Cranke ported top end I would now rather be safe than sorry.

I see a lot of posts about sealing H20 pitting.  My 250 lower end was pitted clear through.  I used what I refer to as "carnival rod" to fill it in.  It's that weird soldering/welding rod you see being sold at fairs.  You know with the guy soldering a pop can to a steel plate.  The rod acts like no other material I've ever welded or soldered with.  It clumps up and absolutely does not flow.  I just heated the case with some MAP gas and began scraping the rod across it through the flame until it began to melt.  I had to scrape and push the material down into the pits.  Once it got in there it really bonds and its extremely strong.  I used a burr bit in a grinder to reshape what had built up.   It looks great and has lasted without problem.

Matthew


WARNING: The Surgeon General has determined that castor smoke can be hazardous to your health.  It is highly addictive and causes delusions of grandeur.

[john durrill]

Matthew,
 can you give me a source for the welding rod and any flux that is needed. sounds like it would work on aluminum to reshape transfer ports.
thanks,
john d.

[Merlin]

..............rather than taking the chance of setting a magnesium case on fire ,I have wondered if powder coating would be a good premanent solution to pitting damage.......................

[john durrill]

Merlin,
KTM used epoxy on small imperfection in the castings when the motors were assembled.. I have never had a set of cases burn when using a torch to heat them. I think it would take some shaving to get the magnesium started and a lot of heat.
 We used a torch to burn holes in a maintance frame work we swiped from the Army in SE Asia. We didnt know it was till we had the magnesium  light off a` few times chuckle` chuckle. But we were cutting holes all the way through with an Oxy Acet cutting tip
John D.