New pistons - which way is front?

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skipseyhughes
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New pistons - which way is front?

Post by skipseyhughes »

I'm about to fit new pistons - Hepolite 14396 030 - but there is no marking on the crown of the pistons to say which way is front. Is this because it doesn't matter? Sorry if it's a stupid question but I'd like to make sure they're the right way round!
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A40FARINAGURU
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Re: New pistons - which way is front?

Post by A40FARINAGURU »

skipseyhughes wrote:I'm about to fit new pistons - Hepolite 14396 030 - but there is no marking on the crown of the pistons to say which way is front. Is this because it doesn't matter? Sorry if it's a stupid question but I'd like to make sure they're the right way round!
there should be the word 'front' on them at least
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Neil Evans
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Re: New pistons - which way is front?

Post by Neil Evans »

Have they split skirts? If so, these go to the non thrust side... :thumbs:
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A40FARINAGURU
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Re: New pistons - which way is front?

Post by A40FARINAGURU »

Neil Evans wrote:Have they split skirts? If so, these go to the non thrust side... :thumbs:
i've just checked a set of 'PEP' pistons, there is no split skirt but no markings of 'front'
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skipseyhughes
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Re: New pistons - which way is front?

Post by skipseyhughes »

Yes, that's correct, they don't have split skirts and there is no indication of "front" :(
Big Daddy
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Re: New pistons - which way is front?

Post by Big Daddy »

skipseyhughes wrote:Yes, that's correct, they don't have split skirts and there is no indication of "front" :(
In the absence of any markings, suggest looking at piston gudgeon pins which are slightly offset towards the thrust face. This is the very reason why pistons have a specific correct orientation. Offset is fairly subtle but it can be seen visually or measured using calipers.

http://pautomotivemechanics.blogspot.co ... signs.html


Thrust face is viewed from front of engine (ie fan belt pulley) in both drawings... :thumbs:
thrust face.gif
thrust face.gif (59.65 KiB) Viewed 517 times
piston offset.gif
piston offset.gif (66.16 KiB) Viewed 517 times
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skipseyhughes
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Re: New pistons - which way is front?

Post by skipseyhughes »

Many thanks - I'll get myself some callipers and try that :D
skipseyhughes
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Re: New pistons - which way is front?

Post by skipseyhughes »

My new calipers arrived today so I measured the the distance from the gudgeon pin to the sides of the new pistons. It seems to be 28mm to either side but I'm still a bit worried I might not be measuring accurately enough. The article says the offset might be something like 1.5mm. Is that what it should be for our engines?
Big Daddy
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Re: New pistons - which way is front?

Post by Big Daddy »

skipseyhughes wrote:The article says the offset might be something like 1.5mm. Is that what it should be for our engines?
Yes it will be close to 1.5mm. If you cannot measure a difference, then pistons are probably symmetrical so can be fitted in either orientation, which may explain lack of marking.

I tried to find specification of Hepolite 14396 pistons but nothing came from the web. Calipers are always a useful tool in your box... :thumbs:
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Dave Clark
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Re: New pistons - which way is front?

Post by Dave Clark »

I,m pretty sure that at least some A series are symmetrical because I have assembled several 1275 engines with unmarked pistons and just made sure that they all looked to be the same way round. I do belong to Bodgers Anonymous as a founder member so don,t take my word for it.
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Re: New pistons - which way is front?

Post by Big Daddy »

Sometimes pistons have been skimmed which removes the markings, so it's always worth checking for gudgeon pin offset. Surprisingly even quite small offsets can be detected visually.

If you can't see or measure any offset, then pistons are probably symmetrical... :thumbs:
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skipseyhughes
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Re: New pistons - which way is front?

Post by skipseyhughes »

Many thanks guys - that puts my mind at rest :)
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