Author Topic: Taiwanese Pistons  (Read 2068 times)

Online Brian

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Taiwanese Pistons
« on: 24.07. 2012 06:21 »
I recently bought a set of Taiwanese pistons from British Only Austria for a customers A10.

There has been a bit of discussion about these pistons so I thought this time I would inspect them a bit closer and see how they compare with the genuine piston. This is the second set of these I have purchased, the first set are in my own plunger A10 but I've only done about 2,000 miles on that particular bike. So far I cant fault them.

Start with weight, the only genuine piston I have to compare is +.020" whereas the ones I have just bought are STD. The genuine one weighs 233 grams and the Taiwan one 222 grams so based on that I would say the weight is almost identical to a genuine BSA piston.

Next is grind, or "ovality". The Taiwan piston has .006" which is sufficient and identical to the BSA one.

The gudgeon pins are a nice push fit.

The rings are no good, once again they have too much end gap. I had the same problem with the first set I bought and once again will use Hepolite rings. I will e-mail BOA and let them know about this. The Taiwan rings supplied with the pistons have .027" end gaps, they should be around .012".

So other than the rings they seem quite good. They were ?130 plus the cost of a set of Hepolite rings which in my case I happen to have. They were the only ones I could find in flat top, 7.25-1 compression ratio.

Finding quality pistons is always a problem, JP's are expensive and depending on what you read can suffer from quality issues. GPM's as far as I know dont come in a flat top 7.25-1. With the exception of the rings these Taiwan ones seem ok.

I always put pistons in with clearance in the upper end of the specified range. The book recommends .003" to .005", I would never go under .004". This particular motor will have .0045" as the bores are good. The owner popped a hole in the top of the right side due to too much advance, too lean and rode it with it pinging like crazy.

Offline Duncan R

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Re: Taiwanese Pistons
« Reply #1 on: 24.07. 2012 18:47 »
Hi Brian,

Just fitted some to my bike. The engineer who resleeved my barrels said they looked fine. The bike runs ok so far so fingers crossed. One of my JP pistons got smashed to bits when the spigot gave way.
Anglo - Indian A7SS (Actually is a 650)
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Online chaterlea25

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Re: Taiwanese Pistons
« Reply #2 on: 24.07. 2012 22:44 »
Hi Brian and All,

The bike I fitted the Taiwanese pistons to is running well, with new old stock Hepolite rings (3000+ miles so far)

I posted some time ago that these are now branded "hepolite" and distributed by Wassel
I'm told that the rings are now American "Hastings" brand
Havn't tried those????
I lashed out and bought a set of Wiseco's for the RGS project (OUCH!!!!)
Cheers
John O R
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Online KiwiGF

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Re: Taiwanese Pistons
« Reply #3 on: 25.07. 2012 01:07 »
As per the other thread a while back ("Eastern Pistons") - I was disapointed not to be able to get "Fuh Jiunn" brand pistons from BOA as by all accounts they are a reputable maker.

I ended up returning some A10 pistons to BOA (due to duff rings and gudgeon pins). Back then BOA could not re-supply the std bore flat tops, so they must have them back in stock now, and also resolved the quality issues with the pins. Unfortunately I've bought JP Pistons in the meantime.

However, one issue that to me still needs considering is that BOA could not (or would not, for commercial reasons?) tell me the brand of piston I was supplied with. The pistons I was sent came in plain boxes and did not have any makers markings.

So, unless BOA would supply an order specifically for "Fuh Jiunn" brand buying pistons from them is like a "box of chocolates" - you never know what you are going to get!
New Zealand

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Online Brian

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Re: Taiwanese Pistons
« Reply #4 on: 25.07. 2012 08:06 »
I just went back and had a look at the "eastern piston" topic to see what happened to you KiwiGF. I'm glad you got your money back.

I cant understand why BOA would not tell you what brand the pistons were, thats strange. I've found them very helpfull.

The pins that came with the pistons I bought are dead on .750". They will go into the pistons without heat but it takes quite a push and thats normal. The only problem I have had is the rings.

I have e-mailed BOA about the rings but as yet have not heard back.

Online KiwiGF

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Re: Taiwanese Pistons
« Reply #5 on: 25.07. 2012 12:29 »
Hi Brian, BOA were really good about it, they even refunded me for the freight to/from NZ, but it was odd that I could not just send the rings and pins back for replacement, they only sell the the pistons as "sets".
New Zealand

1956 A10 Golden Flash (1st finished project)
1949 B31 rigid “400cc” (2nd finished project)
1968 B44 Victor Special (3rd project,in progress)
2001 GL1800 Goldwing, well, the wife likes it
2007 KTM 950 Adventure, cos it’s 100% nuts

Online KiwiGF

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Re: Taiwanese Pistons
« Reply #6 on: 25.07. 2012 13:11 »
Brian, the fit of your pins sounds better than the ones I was supplied but shouldnt new pins be VERY tight when cold, almost impossible to force in? as they should still be a tight fit when hot?
New Zealand

1956 A10 Golden Flash (1st finished project)
1949 B31 rigid “400cc” (2nd finished project)
1968 B44 Victor Special (3rd project,in progress)
2001 GL1800 Goldwing, well, the wife likes it
2007 KTM 950 Adventure, cos it’s 100% nuts

Online Brian

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Re: Taiwanese Pistons
« Reply #7 on: 25.07. 2012 13:46 »
The fit of pins seems to vary, most modern engines the pins slide in quite easily. I've done quite lot of work on modern multi cylinder bikes and the pins usually slide in quite easily on them.

In my experience you need to heat Hepolites to get the pins in but with GPM's the pins slide in easily. When the engine heats up the pin heats up with it and maintains its fit. Its a bit like a bearing in a housing, heat the housing and the cold bearing will drop straight in but the bearing doesnt move when the motor is running as once again it all heats up together.

As long as the pins are a push fit in the piston all will be well.

Online RichardL

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Re: Taiwanese Pistons
« Reply #8 on: 25.07. 2012 14:13 »
It seems to me that pin fit will be slightly looser when the engine is hot,  what with aluminum's coefficient of expansion being greater than steel. Hard to imagine the piston,  exposed to the explosions,  would be cooler than the pin. Of course this hinges on internal diameters increasing with heat per,  "heat the case to let the bearings fit." Does this make any sense?

Richard L.
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Online muskrat

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Re: Taiwanese Pistons
« Reply #9 on: 25.07. 2012 21:05 »
 Tight pins = the No1 cause of bent rods !! "I'll just tap it one more time a little harder."
I prefer a warm push fit. The pin is supposed to be fixed in the piston and turn in the l e bush.
Cheers
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Online Brian

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Re: Taiwanese Pistons
« Reply #10 on: 25.07. 2012 23:33 »
You would probably need advice from someone who is an expert in the particular field of gudgeon pin design to answer these questions correctly but in my experience there are three basic set ups.

1. The pin is fully floating, a push fit in the piston and small end bush.

2. The pin floats in the piston but is trapped in the small end, common in car engines.

3. The pin is trapped in the piston and moves in the small end bush.

As to which one of these, if any, is better or worse I dont know, they are all used successfully in a variety of engines.

Muskrat brings up a good point worth noting, do not ever hit a pin to install it. If it wont slide in get a pin pusher, they are available quite cheap on the net or at most automotive accessory places.

Online KiwiGF

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Re: Taiwanese Pistons
« Reply #11 on: 26.07. 2012 05:32 »
Hi Brian, I still regret sending the BOA pistons back as also found them fine dimensionally. I could not actually measure the fault with the pins with a mic. They were just fractions of a thou undersize, I was only certain it was the pins and not the pistons at fault as some used pins I tried were the right fit in the BOA pistons.

On Dutch's recent thread about con rod eye size a discussion started on crank balancing, I'm now realising that the lightness of the BOA pistons would have gone a fair way to reducing the number of holes in the crank I will need to compensate for the billet rods I am fitting.

Maybe I'll end up buying another set of pistons from BOA and sticking the new JP's on the shelf...

Below is an email I got from JP some time ago, I am not sure if the weights given are including pins/clips/rings.

Out of interest I've found some pins are significantly lighter than others as they have thinner walls and/or have tapered bores so it might be worth checking what BOA have supplied to ensure any advantage from the light pistons is not wiped out by the pin weight!


"Hi Simon,
 
JP0642 cost is A$131.82 per piston assy, weight is 351grams
 
JP0652 cost is A$115.95 per piston assy, weight is 343 grams
 
Post Approx A$44.95
 
Regards
 
Peter"
New Zealand

1956 A10 Golden Flash (1st finished project)
1949 B31 rigid “400cc” (2nd finished project)
1968 B44 Victor Special (3rd project,in progress)
2001 GL1800 Goldwing, well, the wife likes it
2007 KTM 950 Adventure, cos it’s 100% nuts

Online Triton Thrasher

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Re: Taiwanese Pistons
« Reply #12 on: 26.07. 2012 06:45 »
Tight pins = the No1 cause of bent rods !! "I'll just tap it one more time a little harder."
I prefer a warm push fit. The pin is supposed to be fixed in the piston and turn in the l e bush.
Cheers

Hot push fit works well in an old bike engine.  So does cold sliding fit, so there's not all that much to fret about really.

Online muskrat

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Re: Taiwanese Pistons
« Reply #13 on: 26.07. 2012 10:15 »
 When you think about it "2. The pin floats in the piston but is trapped in the small end, common in car engines." would be better for rigidity as a bit of wear would not cause as much piston rock as a worn little end bush. But would the piston bore wear faster than a bronze bush? And a bit more friction heat in an already very hot part.
 Think I'll stay with what I've got. MC forged offset pin 10.5:1 racing slugs. Hot piston push in pin.
Cheers
'51 A7 plunger, '57 A7SS now A10CR,  '83 CB1100F, 88 FXST .
Australia
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Offline duTch

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Re: Taiwanese Pistons
« Reply #14 on: 26.07. 2012 14:05 »
Today I measured up my pistons/bore, and the pistons(Æ-that's hepolite hey? new in early '80's) have an ovality of about 14 thou under rings and ~10 thou ovality at bottom of skirt.
  Going on Brians' figure of 6 thou, is that excessive?? They haven't had a lot of use-fairly much still look newish.
   They are tapered 8thou o/a (4+4)up the sides, and 2thou o/a (1+1)up/down fore and aft.
 Hope all that makes sense?
 I'm not freakin' out or anything-just curious if that's normal, and so's I know what's where- they'll get used anyway.
 Am waiting for eScales to arrive so can weigh them again.
 Cheers
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