piston assembling

Top End (cylinders pushrods etc.)
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hjans
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piston assembling

#1

Post by hjans »

Hi there
Today i removed the cylinders .
Inspected the lot, and it all seems to be quiet ok. No excessive wear whatsoever
except for one thing : the pistons seem to be installed the wrong way !
Always thought the web-mark should point to the right side of the engine, as the manual says.
But these ( on my engine ) point to the left side !
See pics below.
Question : These pistons are Zodiac i think. Is it possible they should be assembled the "wrong " way ? What could happen if they where assembled the wrong way ? Can i turn them the right way without changing anything else ?

Also removed the gear cover. Pulled the gears out and inspected them. I noticed some wear in the breather valve/gear hole. Think there ever has been debris in there.
I was told that there are plastic or teflon breather valves/gears available, and that i should install one of them to avoid damage if something entered the breather. What is your opinion on that ?

Removed the tappet guides.
They are missing a bit of material : broken off ( see pic ).
Is this a big problem ? Can it be repaired or do they need to be changed by new ones ?
I guess since the four screws only have to keep in in to place, i could try to weld them up.

You see : one madman can ask more then 1000 wise man can answer .
Hope there are more then 1000 of you out there, because i will have to ask a lot more i'm afraid !!

Thanks !!

Hans
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Panacea
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Re: piston assembling

#2

Post by Panacea »

I've heard the plastic breathers get impregnated with debrix and scratch the hell out of the bore...Mike
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Re: piston assembling

#3

Post by mbskeam »

plastic breathers hold onto metal and this scores the alum, a few minor scores does not seam to hurt my cases, but this can be oversized or rebushed to std if need be

does the piston have a mark on top?

weld up the blocks


mbskeam
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Re: piston assembling

#4

Post by Cotten »

The pistons appear backwards to me.

There is no justification for a plastic breather.

The tappet blocks are an easy weld repair, but in light of the other concerns I would suggest arbitrarily replacing the tappet rollers.

....Cotten
hjans
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Re: piston assembling

#5

Post by hjans »

mbskeam :
No marks on top of the pistons, only the size
Hans
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Re: piston assembling

#6

Post by fourthgear »

The pistons do look backwards ,but that would depend on the manufactures instructions.If the cylinders are worn enough that you will have to go over sized pistons after boring ,it does not matter what way those particular pistons were put in .

Weld the tappet guides , as said by others . You see those tab holes broken even on the cast steel guides.
hjans
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Re: piston assembling

#7

Post by hjans »

Thanks you all.
Pisons and cylinders show no excessive wear, so i don't plan on replacing them.
Think i send an email to zodiac asking their comment.
What would be the problem when assembled the wrong way ?
Can i turn them around if so ?

Hans
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Re: piston assembling

#8

Post by Cotten »

hjans!

Often, but not always (such as with oriental sportster slugs), the wristpin is offset slightly within the piston. This is what gives it a 'front' or 'back'.

If you use a caliper to measure from the outside thrustfaces to the opposite sides of the installed wristpin, then a comparison will quickly tell if the pin is offset.

Trying to remember makes my forehead wrinkly, but I believe they are to be offset toward the front thrustface of the piston.
(I've got a 50/50 chance of being right.)

....Cotten
hjans
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Re: piston assembling

#9

Post by hjans »

Cotten
Thanks a lot !!
Can you please explain "thrustface "?
I'm from Holland and don't know al, tech terms ( but a lot already and still learning !!)
Browsing the net does not bring an answer, so.....

In your experience, would mounting the pistons the wrong way ( wich appears to be the case with my Pan ) cause damage or even excessive damage ? Guess nobody tried this, so i can imagine nobody can answer this by experience !!
Thanks.

The pistons used are JCC, can i use the old clips for the wristpin ?
Only can find "original "style ( NOS-parts ) , nobody over here sells the JCC piston pin lock rings apart.
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Re: piston assembling

#10

Post by Cotten »

jhans!

Pistons are not round, but cam-shaped, with their greatest diameter in the middle of the front, and in the middle of the rear; These are the thrust faces as that is where the piston encounters the most thrust upon the cylinder walls.

Naturally the front sees more thrust than the rear, and that is the reason for the pin offset.

I would use fresh, new retaining clips of the design you found installed: common snap rings?

....Cotten
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Re: piston assembling

#11

Post by steinauge »

A piston may be directional for 3 reasons,1-wrist pin location(Evo and twin cam pistons) 2-valve relief size(iron XL) 3-skirt shape (look at the pistons for a 113"S&S) Of course you may have all 3 on the same piston too! Your pistons are not directional,they are copies of the H.D -73 type piston.Once they have been run they need to be reinstalled the same direction they came out.the "directional" lugs on the bottom make it simple to tell which way the piston was facing if it is taken off the rod.I know some of the HD service manuals tell you to face the lug to the right but it really doesnt matter. I heard this at HD service school in 1975,1980 and 1982.The first OEM directional piston for the pan and shovel engines came out in late 82 and is marked "Mahle" inside the skirt.On these the directional lug faces to the left or clutch side of the engine.HTH
hjans
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Re: piston assembling

#12

Post by hjans »

Thanks steinauge.
Hope you are right about this !!
I removed them already and assembled them the other way around.
I might just change it again.

Hans
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Re: piston assembling

#13

Post by DeltaElite »

Hoi Hans,

what happended thereafter? I am facing a similar problem.

Cylinder have been bored and honed and a new .050 Piston-Set has been mounted by the previous owner. He gave up on the bike and sold it and when handing it over he mentioned that it might be that the pistons are mounted with the web on the wrong side. But he's not 100% sure.

I want to avoid to remove cylinder-head and cylinders just to find out that they are mounted with the web to the right (correct) side when it really doesn't matter if the cylinder and piston are new.

Any suggestions?
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Re: piston assembling

#14

Post by RooDog »

If you are asking the question, then must mean something to you, and if you don't open it up to make sure if they are correctly installed, you will never know for sure, and it will always be there in your mind every time you ride.

It is more of a mental issue than of mechanical concern. But, as mentioned elsewhere, if the previous owner was not sure how he assembled the pistons, and gave up on the bike, then what else has he compromised.

As Harley owners we are constantly assaulted with problems needing to be overcome, and it is only by perseverance that we adapt to, and overcome these obstacles....
Best Wishes....RooDog....
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Re: piston assembling

#15

Post by Andygears »

DeltaElite! Maybe it’s just my memory, or remembering only 80 inch flywheels (4 1/4 stroke) but I recall my pistons have a small flat at the inboard bottom edge. This is so that at bottom dead center, the skirts do not touch each other. If they hit each other, it makes a small click, at the bottom of the stroke, when rolling over by hand with no spark plugs. I believe this small flat gets bigger as the over size increases.

So, never mind the web, or an arrow, these flats must face each other or the pistons will kiss!

Andygears
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