Author Topic: Riding the Old Route (Read 5109 times)

baird4444 · **on:** October 07, 2011, 02:10:41 pm

early in August I took off for a stretch of old Route 66 just south of Bloomington, Illinois. I used http://www.historic66.com/illinois/det-il3.html as my map and tour guide. It was fun to know the history and see the funky sites as I went thru each little town. One of the highlights for me was the giant "weiner guy" in Atlanta.
While riding around in Lincoln looking for lunch, a guy pulls up and we start talk'in motor cycles. Seems he had this 78 GL 1000 that he had bought from California but thought was to big.... he had old BSA's in the past and wanted sum'thin a little smaller for running around town. Sight unseen I offered a trade, gave him my card and told him to think about it.... this opened my mind to other motorcycles....

a couple of days later as I was cruz'in the cornfields of central Illinois I heard what sounded like the clatter of a rock circling the front tire and rattling on the fender; but then I was DEAD. I coasted to a stop and realized that I could roll in 4th gear; not good. Absolutely no compression. My 1st guess was the piston but my hope was a pushrod lodged up holding a valve open... NO SUCH LUCK!!

2 days later I get an email from the guy in Lincoln asking me if I was serious?
it's been a shitty year for me when it cums to motorcycles!

baird4444 · **Reply #1 on:** October 07, 2011, 02:24:14 pm

The damage was done. Piston top had separated and the cylinder was scored.
The good news; if there could be any; was that this piston had less than 2,000 miles on it from from October of last year. A very wet and cold spring made the break in take forever this year. Slam Dunkus warrantied his work and CMW warrantied the piston; hell they even went one better and upgraded to a forged job! Because of the scoring and since the old on a fresh .020 over; he had to go to a .040 over....
I gotta praise Slam at
http://www.interstatemotorcycles.com/
for the way that they backed the previous work. I didn't get it back till the
end of September for the Rally on the River..... like I said, a shitty year.

r80rt · **Reply #2 on:** October 08, 2011, 03:09:10 am

Glad they got you back on the road, Slam is a damn good guy.

mrunderhill1975a · **Reply #3 on:** October 08, 2011, 04:28:03 am

What is the verdict on the cause of the separation? Too hot?

Looking at the design, there isn't much metal holding the top on with the oil slits.

scoTTy · **Reply #4 on:** October 08, 2011, 04:57:27 am

well as far as riding the olde route... I did it all all the way to Cal i ,, when the freeways let me..

http://www.youtube.com/watch?v=dCYApJtsyd0

sorry about your piston... wow.. never saw one broke so clean

ScooterBob · **Reply #5 on:** October 08, 2011, 08:57:56 am

Quote from: mrunderhill1975a on October 08, 2011, 04:28:03 am

What is the verdict on the cause of the separation? Too hot?

Looking at the design, there isn't much metal holding the top on with the oil slits.

That is a pretty common Iron(ic) Barrel failure - there is literally nothing but four dabs of alloy holding the piston crown on - and if the Raj pouring the alloy in the mold sneezes .... well ...... The OEM piston will hold up OK IF you don't rev the engine at all - like riding it at 45mph .... Over time and at speeds, the crown becomes "heavy" (F=m x a) and breaks the tabs. A forged "real" piston is the trick to actually RIDE and Iron(ic) Barrel .... or at least a good aftermarket design that has some meat in the oil ring groove .....

mrunderhill1975a · **Reply #6 on:** October 08, 2011, 06:32:01 pm

"and if the Raj pouring the alloy in the mold sneezes .... well ......

A forged "real" piston is the trick to actually RIDE and Iron(ic) Barrel .... or at least a good aftermarket design that has some meat in the oil ring groove ..... "

I see in the photo what you mean.....on the left side of the photo the metal seems to have bubbles and voids...there is one that looks like a worm. So the trick is to get a forged piston......in that regard.... how is a forged piston made? Do they just get a hot cube of metal and bash it until it is shaped like a piston?

barenekd · **Reply #7 on:** October 08, 2011, 07:00:37 pm

Quote

Do they just get a hot cube of metal and bash it until it is shaped like a piston?

Basically, but that is better than having a cup of molten aluminium and pouring it into a sand mold and hoping all the air is out.
Bare

Arizoni · **Reply #8 on:** October 08, 2011, 11:24:18 pm

Not only will a correctly forged part not have voids in it, it's grain will be running in the direction where the stress is developed.

Wrought metal has a grain, somewhat like wood and if a forged piston is done right the grain will flow around holes like the wrist pin and it will be going up thru those thin areas like the places where the piston in the photo failed.

Cast parts have very short crystal like grains that run in random directions so they really don't contribute to the parts strength.

This explains why forged connecting rods and pistons are far stronger than cast connecting rods and pistons even if they are made from the same alloy.

ScooterBob · **Reply #9 on:** October 09, 2011, 01:24:56 am

Guys - Don't also forget that the forging process itself CRAMS the metal together and makes it more DENSE as well - hence the stronger part. I've used some really good cast pistons over the years - the technology now is pretty good - but forging wins for the indestructible slug ......

mrunderhill1975a · **Reply #10 on:** October 09, 2011, 02:35:23 am

Thanks guys, this has been a very informative thread. It is my understanding that the forged piston would need a larger cylinder bore because of more expansion needed for the forged piston? Is that correct? If so, would there be more blow-by and more oil consumption?

Ice · **Reply #11 on:** October 09, 2011, 04:31:30 am

No Sir.

The piston quickly expands and normal clearances result and besides, its the rings are doing the sealing.

scoTTy · **Reply #12 on:** October 09, 2011, 04:42:32 am

I'm trying to remember the forged piston thing and drag racing autos in the 60's.. need help as I have cobwebs of the brain...

forged pistons take longer to expand due to ther density.. so they are set up loose in the cylinders.. lots of noise until they warm up .. am I remembering right?

Ice · **Reply #13 on:** October 09, 2011, 05:39:22 am

Pretty much BUT,,,,drag car engines had their pistons fitted looser than street cars to reduce power robbing drag induced friction when every pony power was need to win.

Side wall clearance of .008 and sometimes more were common

The local season winner back home was running an engine fitted to clearances that that the factory would consider beyond service limits.

Arizoni · **Reply #14 on:** October 09, 2011, 05:55:41 am

If you don't like numbers you might want to skip this engineering crap.

My data says there is very little difference in the density between most cast or forged aluminum's.

For instance a cubic inch of forged aluminum weighs around 1.568 oz. to 1.616 oz depending on which alloy is being considered.

A cubic inch of cast aluminum weighs around 1.488 oz to 1.632 oz depending on which alloy is being considered.
Putting this into a real world example, if a piston contained 7 cubic inches of aluminum the differences in weight would be .44-.89 ounces depending more on the alloy than the process which formed it.

Thermally the aluminum castings expand between 10.7 x 10^e-6 to 13.3 x 10^-e-6 inches/degree F/inch
Thermally the aluminum forgings expand between 12.2 x 10^e-6 to 13.9 x 10^e-6 inches/degree F/inch.

Putting these numbers into the real world, say for a Royal Enfield Piston with a 3.3 inch diameter at 300 degrees F the lowest expanding cast aluminum would grow .0106 and the highest expanding forged aluminum would grow .0138.

Obviously the alloy is more important than the method of forming when thermal expansion is involved.

Usually the forged pistons have thicker walls which take longer to heat up.

baird4444 · **Reply #15 on:** October 09, 2011, 11:57:52 am

Slam did tell me that the piston is "a little loose" and there might be some
piston slap till she's good and warm. Said that's a whole lot better than
having it seize.
as I said in my origanal post my mind was opened to bigger bikes...
While waiting for the rebuild I found this 2005 VL800 Boulevard
that I stole. She who must be obeyed declared that the Enfield
must go to recoup some of the cost...
She is right. I don't love the new one like the Enfield but I
do love the ride.
- Mike

Chasfield · **Reply #16 on:** October 09, 2011, 01:38:33 pm

I bet that in many of these piston failure cases, the crown separation is a secondary effect of the skirt overheating, seizing in the bore and being left behind as the rod punches the crown away from it. Though I don't doubt that a bad casting will set you up for a more spontaneous separation.

Were there any signs of the piston skirt nipping up in the bore in this case?

t120rbullet · **Reply #17 on:** October 09, 2011, 02:21:50 pm

Does Swmbo know how much a whole new set of motorclothes is going to cost you?
You going to get a Doo Wrap ?
Your going to miss that Enfield !
CJ

ScooterBob · **Reply #18 on:** October 09, 2011, 03:14:53 pm

Quote from: Chasfield on October 09, 2011, 01:38:33 pm

I bet that in many of these piston failure cases, the crown separation is a secondary effect of the skirt overheating, seizing in the bore and being left behind as the rod punches the crown away from it. Though I don't doubt that a bad casting will set you up for a more spontaneous separation.

Were there any signs of the piston skirt nipping up in the bore in this case?

Nope - Usually the crown parts company right at the oil ring groove! The barrel skirt, pin, rod and all that jazz just keep going up and down with the big hole i the top .... Most of the time the crown will just go up, STAY there and the bottom of the engine will whiffle to a halt - and a new piston and a light hone will cure all. It's the gentlest catastrophic engine failure you could ever have .....

prof_stack · **Reply #19 on:** October 09, 2011, 07:14:59 pm

Quote from: baird4444 on October 09, 2011, 11:57:52 am

...
While waiting for the rebuild I found this 2005 VL800 Boulevard that I stole. She who must be obeyed declared that the Enfield must go to recoup some of the cost...
She is right. I don't love the new one like the Enfield but I do love the ride. - Mike

Wow, what a great looking motorcycle! Congratulations and safe riding to you!

You love the ride - well, isn't that what it is all about?

baird4444 · **Reply #20 on:** October 09, 2011, 09:18:27 pm

Quote from: t120rbullet on October 09, 2011, 02:21:50 pm

Does Swmbo know how much a whole new set of motorclothes is going to cost you?
You going to get a Doo Wrap ?
Your going to miss that Enfield !
CJ

   Thanx for the support cj....
   no, you aren't going to see me in the pirate suit...
or assless chaps...
   Argh!!!

baird4444 · **Reply #21 on:** October 09, 2011, 09:26:24 pm

Quote from: Chasfield on October 09, 2011, 01:38:33 pm

I bet that in many of these piston failure cases, the crown separation is a secondary effect of the skirt overheating, seizing in the bore and being left behind as the rod punches the crown away from it. Though I don't doubt that a bad casting will set you up for a more spontaneous separation.
Were there any signs of the piston skirt nipping up in the bore in this case?

there was some scoring in the bottom half of the jug with 1
real nice groove full length. I'm guessing caused by the non
existent oil ring.

t120rbullet · **Reply #22 on:** October 10, 2011, 12:33:13 am

Quote from: baird4444 on October 09, 2011, 09:18:27 pm

Thanx for the support cj....
no, you aren't going to see me in the pirate suit...
or assless chaps...
Argh!!!

How about ink ?
No charge for the support, it's the least I could do.
Your still gonna miss ole greenie.
CJ

Leonard · **Reply #23 on:** October 12, 2011, 04:50:57 am

Take it from me Mike, you're going to miss that RE.