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B175 Top End Questions
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Danny
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July 30, 2019 - 4:31 pm
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Just put my B175 back on the road and took it to mates who knows a bit about 2 strokes ( I don't and have rebuilt the bottom end myself 😨)

It's running fine or seems to be but has a slight top end rattle , More noticeable when let off revs and it settles back to idle. Mate says he would maybe put new piston and rings? Im just wondering what I need to check I'm guessing pull the barrel off?

Other thing is the piston is stamped what looks like +0608L which I'm guessing is a+60 the last over bore. Barrel and piston looked unmarked so would just fitting new rings be possible?

As you can tell I'm not clued up on piston and rings lol

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AdrianS
Harlaston Staffs
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July 30, 2019 - 4:54 pm
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2 strokes do sometimes sound like the top end is rattling a little. Very difficult to diagnose a problem online without hearing or looking under the head.

Top end rattle can be caused by piston slap or little end wear. I'm afraid the only way to check correctly is to take off the head and barrel: you can then see if any play is perceptible in the little end bearing. If that feels ok you will need to remove the piston and measure the clearance in the bore ( with the rings off) at different positions in the barrel. This is done with feeler gauges down the side of the piston. The rings generally are checked by seating them in the barrel and measuring the gap between the ring ends. If it is wear in the piston, then new rings will not cure the problem.

Not sure about the number on your piston. A pair of calipers across the body of the piston will measure the approx. diameter and then you can tell how many times the barrel has been bored out by the size of the piston. I'm not 100% sure but if you running at 60 thou over then you probably would need a new barrel as it has been bored out to the maximum ( I think Rex Caunts Suzuki pistons are 60 thou over bore which is bigger than BSA pistons would run to).

The workshop manual will give you exact figures and if you haven't got one im sure someone on here will post them! I would but cannot get into my garage at the moment.

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Danny
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July 30, 2019 - 6:04 pm
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Many thanks for the reply ,I do have a workshop manual so I'll dig it out 

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BASIL
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July 31, 2019 - 10:11 am
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Hi, before you go to the expense of stripping the engine down the first thing to check is the slide in the carb these have a tendency to rattle if worn and it's a very misleading rattle, to check run the engine with the air filter removed so you can put you finger against the slide, if you push against the slide and the rattle stops then there is you problem if not then "dig" deeper. Regards Basil.   

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Mannanan
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July 31, 2019 - 10:29 am
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You say you are not that familiar with two strokes so maybe what you are hearing is pretty normal for a Bantam. I rebuilt my B175 which included rebore, new piston and rings. You would never call it smooth and quiet, it’s what I consider the normal ring a ding ding for a two stroke. What’s the performance like on yours? Does it smoke badly? Will it pull reasonably well up a gradient?

Ed.

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Danny
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July 31, 2019 - 5:56 pm
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Carb is a recon jobbie but I'll definitely check!

Seems to pull o.k with no excessive smoke but I've nothing to compare it with really. My mate is up on 2 strokes and says its a top end rattle. I could try and do a video but noise usually sounds totally different on the phone.

I know a guy that had bantams when they were new and is very clued up so I'll let him have a Liston to it 👍

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SpacedMarine
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July 31, 2019 - 9:02 pm
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Screenshot_20190731-210441_Gallery.jpgSure it's not the primary chain?Just the fact the noise is when you let the throttle off.Under load the top run of the chain is taught.when you let off the chain tension moves to the bottom run.Im sure most people who've opened a bantam up will have seen the tell tale signs of a worn chain wheres its hit the inside of the case.Just a thought.

What's 7/16 in mm again?

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nickjaxe
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August 2, 2019 - 3:00 pm
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Carb slide rattle as others have said or maybe as James says the primary chain.

They are rattle things at the best of times.

My Bantam video              https://www.you.....jpOFmzRZRI

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