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Discussion Starter · #1 ·
I'll try to make this short and to the point. I had my cylinders bored to .070" over. Just a quick fix for now. I left the heads alone. I was about 50 miles short of my 500 mile oil change, and she locks up going down the highway. Mind you, we've had 100 degree weather here for the last couple of weeks. Not the greatest conditions to break the rings in. Upon tear down. My rear piston is seized to the rod, and possibly the rod to the crank as I can't get the piston to come up enough to remove the pin. The thing is, after looking at the front piston i noticed damage from the pistons hitting each other, and the piston skirt was hitting the flywheel. I compare the piston with the ones that were pulled recently. The old ones were clearanced on the forward and rear edges of the skirts. And my new set was not. You can see the two in the pics. Notice the damage on the new piston. My question is why were the new pistons not clearanced? I assuming the pistons hitting the flywheels are a result of them hitting each other. All of the measurements were identical on the new and old pistons minus the relief. Why is this not mentioned in my clymer? If this is a possible issue, why didn't the shop mentioned it to me? The lower end has to come apart to be able to remove the piston. There are also shavings from this damage in my cases, which makes me wonder if one of my oil passages got blocked.
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did you just pull the jugs and old pistons and bring them in to be measured and machined ?
and then you re assemble the top end at home ?

what bore were the old pistons ?

if the shop that did the machine work had you whole motor there and did not check for clearance upon assembly then thats on them i would call and speak to them about it
 

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All that I brought them were the jugs. They were at .050 and one of them didn't clean at .060. Is this just simply a $250 lesson to add to my repitoire, by not knowing to check for this?
i hate to say it but i think so
im with drag i dont see how the bearings would lock up either ?

either way though your gonna be looking at a full tear down to fix what you have now

sorry to hear the bad news man
 

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Discussion Starter · #7 ·
I don't see the connection of the pistons causing the rod to lock up on the pin..

Granted when a blow-up happens it's a chain of events....But that would be really odd for the rod bearings to lock up....
My guess is that the shavings form the pistons hitting eachother, and the flywheels blocked an oil passage causing it to overheat and then well, go to shit.
 

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A Scenario.....

Let's say that the rod bearing was going out.....That would have been very much of a loud knock...Hard to hear if you are running drag pipes..

That amount of play in the rod bearings would allow the pistons to play tag...
Causing what you are seeing on the bottom of the shirts ...

Upon tear down...there will be signs of what the real cause is....

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On the shaving.....

What damage (Cuttings) was done in the flywheel compartment will be pick up by the wheels and sent to the breather oil trap at the back of the case...This is then expelled by the breather gear (A word on the gear, It has a screen to keep most cuttings trapped in the gear) into the camchest, then makes it way to the return side of the oil pump to be pumped back to the tank...Once it does that...It can be picked up by the feed gears and under force, fed to the top end and pinion shaft to oil the rod bearings...

All other cuttings will be surface contact, Cam, Lifter Rollers, C.B. gear, Gen idle gear, Pinion Bearings, Bushings, Cam bearing...Etc...
And that poor breather gear case bore, if it seen mega cuttings it will be in sad shape.



Well.....
Wished that I was full of Good news...
But when engine damage occurs..There is never any good news there...

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lets hope that there is a screen in the gear..



Alot of the times...They have been mod. for added performance of internal breathing....

Or no screen at all...



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Wonder what damage went down on the .070 fresh bore...
Can do a clean up at .080 over....It's the end of the line at max oversize pistons..

Will be time for a new set or sleeve your old jugs and start over at STD bore..
Not many people do sleeves anymore cause of the cost of them plus labor.
The imports are much cheaper...

Not all piston have the same wall fit...
What your pistons look like is the OEM cast with the steel expansion strut.
They fit up at about .001 wall fit..
If the bore does not have deep cuts in them, could get a set of forged pistons at the same oversize bore of .070 and hone out about .002 to .003 more meat for their wall fit..

Just may clean up what you got.

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Raynoslo!

At .070" overbore, the cylinders' spigots will distort as much as three thou inward, and three thou outward, from the basenut stress alone.

If your bore and hone was not performed with stress plates, and the cylinders installed to the same torque, you set yourself up.

When fitted while stressed, 74" cylinders can be taken as large as .100" over.

.....Cotten
 

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Cotton.....

Who makes those pistons in a .100 over for the 74" 3-31/32 stroke

Are they a special order deal...????

Got a few sets that have been maxed out ...
Like to get them back on line..Without popping sleeves in them..
Dragstews!

I always got them from Dixie, and they were identical to the Superior pistons sold by major distributors. ("JCC" or whatever.)
Ross and other companies will make anything you want.

Every cylinder must be carefully inspected, of course, as previous pokes from boremeisters might not have been as masterfull as hoped, an the bore may no longer be n the center of the casting core.

Our first requirement for an educated assessment is to find a way to measure the remaining casting thickness.
I removed the top spring from a common caliper so that the thumbscrew could be reversed, thereby making it openable to clear the baseflange, after setting to a feel for the thinnest spot.
Re-closed, the gap can be measured with a feelergauges, or a dial caliper if large enough. (First attachment.)

The thinnest spots in the cylinder wall are in the milled cuttaways for basenut clearance. I probe the radius of the cut to determine the minimal point, and set the caliper. (Second attachment.)

With 74" cylinders at .100"-Over, and 61" cylinders at .155" over, I found .070" remaining, and have adopted this figure as the minimum safe thickness.

This does allow a margin of safety, as I have an oriental cylinder that ran at what appears to be about .005" wall.
I put my fingernail through it!

(Third attachment.)

....Cotten
 

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Dragstews!

I always got them from Dixie, and they were identical to the Superior pistons sold by major distributors.

Ross and other companies will make anything you want.

....Cotten
Thanks...

Found them for $15.00 ea. cost...Made by "Art Metals" in Japan OR in Taiwan in a related factory....

Like that.....

I have been down the road with Ross, J&E ...
They want you to buy at least 4 pistons before they will made up a special....That's about $500 to $600 for four...:eek:

In this area of the motor....You get what you pay for...:p

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Well...

Think I would bite the Bullet and spend the Bucks and Time to install some LA Sleeves and start over at STD bore...



But ..That's just me Guys....
Ya'll do what feels good to ya and be happy....

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