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Large piston ring gap
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JustinW
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October 3, 2019 - 7:20 pm
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I read on the forum about checking piston rings by sliding them into the bore and gapping them.

I had the head off so thought I'd try it.

You can probably see, the gap is huge (100 thou at a guess!).

I'm new to all this, so my question is... it is possible for piston rings to wear to this extent? Do I just buy a new set of rings and hope that the gap becomes within spec, or am I deluding myself and it's something more serious? 

thanks

 

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nickjaxe
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October 3, 2019 - 9:10 pm
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I'm with Mick...prob not Bantam rings...you need to measure the bore to find out what size you should have.

Have you got a pic of the piston....any size on its crown?

Nick.

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

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JustinW
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October 3, 2019 - 9:52 pm
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Thanks for replies, I'll get a pic of the piston. I measured piston with vernier calipers and got 52mm., but I'll double check. Might be a couple of days till I can take photo.

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Stoo63
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October 3, 2019 - 10:05 pm
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Looks odd, Justin. Obviously too much gap. How snug is the piston in the bore? Is that a bit of a lip at the top of the bore there as well? As Nick says, check the crown for any markings, although sometimes they can be a bit hard to decipher.

Good luck

Stewart

'52 D1 direct lighting plunger; '58 Square Four (project); '55 D3 Battery; '59 D1 direct lighting plunger;  '59 Tiger Cub; '60 5TA;  '76 FS1-E '97 Honda Sky SGX50.

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JustinW
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October 3, 2019 - 10:35 pm
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I thought the piston was quite snug, but I'm no expert. Given the concensus that something is amiss, I'll order some standard rings and see how they fit. if still a big gap I'll delve deeper. 

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nickjaxe
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October 3, 2019 - 11:00 pm
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Save wasting your money...get an accurate measurement and report back.

Which engine is it.

Std 175 bore is 61.5mm...thats out of my B175 manual...is yours a 125/150.

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

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Stoo63
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October 4, 2019 - 12:07 am
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It's a snazzy D1, Nick, so the standard bore should be 52mm. Then upwards in increments. I'm currently experiencing a similar kinda thing with a '52 D1 I've been building out of a box of bits. The piston that came with the barrel was way too small and had similar ring gaps.  It has no markings at all. I've got a +20 piston that is snugger but I fear the bore may have gone a bit oval as the piston is very tight facing the right direction butslips in when rotated 90 degrees. Then I've got a lovely +60 Wellworthy piston that I might just bore it out to. I'm going to take the whole kit and kaboodle down to the local engineering works, slap it on the table and say " Give me compression" - the reading I took with the "original" piston was 25psi rofl rising to about 65 when I put some oil down the plughole. The +60 piston has a diameter of 54mm. I think, Justin, that , like Nick says, you'd be as well taking some measurements rather than forking out on a set of rings that might not do the business. Get one of those digital calipers it'll make life much easier and cheaper in the long run.

try this ** Please log in to view **

other digital calipers are available!

Stewart

'52 D1 direct lighting plunger; '58 Square Four (project); '55 D3 Battery; '59 D1 direct lighting plunger;  '59 Tiger Cub; '60 5TA;  '76 FS1-E '97 Honda Sky SGX50.

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JustinW
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October 4, 2019 - 4:43 am
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Here's the piston top, it looks like STD printed on it. 

Couldn't resist those digital calipers - I'll get those in the first instance and report back.

It is a 125cc D1. There is a small lip at top of barrel.

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carpetralph
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October 4, 2019 - 6:56 am
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You can almost see down the side of the piston. Looks like re bore time. You are lucky though that it is standard, so you may get away with +40 (looks like it may already be past +20).

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Stoo63
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October 4, 2019 - 8:51 am
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You'll be going around the house measuring everything with your new toy, Justin!

Looks, as Ralph says, like you've got plenty wear there. Time for rebore and new piston methinks. After sitting for so long,it makes sense anyway and is going to give you much improvement. Measure your bore and see what you've got.  Then take it from there. How is the rest of the bike coming along? Looks like a great project.

All the best

Stewart

'52 D1 direct lighting plunger; '58 Square Four (project); '55 D3 Battery; '59 D1 direct lighting plunger;  '59 Tiger Cub; '60 5TA;  '76 FS1-E '97 Honda Sky SGX50.

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JustinW
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October 8, 2019 - 7:12 pm
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Hi all

Well I ummed and arred, but had a gut instinct the rings I had were simply wrong. So I ordered a pair of new standard size rings from Rex G on ebay. Only a tenner, and figured if wrong size then I'd simply flog them on again. Well these fitted into the barrel much tighter closing the gap right up. Other measurements confirmed the piston was still exactly 52mm. Bore to barrel measurement was a gap of only 6 thou. The photo of the piston is deceptive due to shadow all round. I figure that for now it will be good to see if I can get the engine to run and take it from there. Yes there is some bore wear, but perhaps not urgent to get rebored, it's not a racing engine after all.

I've put the head back on, taped a piece of bin liner over the carb inlet on barrel and turned it over and the liner was sucked towards the piston, so there is some draw from the piston. I'm waiting for a little mini test petrol tank to arrive, so I'll then make a little frame for the engine and see if I can get it to start.

I'm not going to have time to do a full 'restoration' thread, but Steve did ask how I was getting on, so I'll give some news here.

I've now stripped the engine both sides without splitting, just to learn what is what and have a good nose around. Everything has been present and correct with no wear I can detect, so put it back together again. Bearings seem OK. Clutch plates and spring ring seemed fine. I knocked up a simple clutch nut removal thingy by bending up the sides of an old clutch plate, putting a screwdriver through, and found a plug box spanner was the perfect fit for the nut. 

The primary drive chain seemed fine, but what a hassle getting the split link back on.

I also did some painting using some cellulose I had mixed into spray cans. The colour I had matched is called Aircraft Grey Green, paint code 283 381C. I've primed and painted the frame, brake rims, bits and bobs. I've fitted the footrest and stand and brake pedal. I'm really pleased with colour match, the photo doesn't show the colour properly due to flash. The Cellulose is so easy to use, it dries to quickly and the quality of the spray from the cans is amazing (purchased from auto pain shop).

http://www.dimestream.co.uk/images/brake.jpg

Lot's of other bits to be getting on with, I'm going to do the rear suspension next, I've got new rubbers, just going to spray the spring covers and pop them back on. Next to do is the forks - dismantle and check, then respray and fit to bike.

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nickjaxe
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October 8, 2019 - 10:07 pm
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Did you give the bore a hone to give the ring something to bed in on...take forever otherwise?

Nice work.

Make sure you have enough end gap as well...for a 175 its min 9tho max 13tho...you need a gap when cold so the ends dont meet when hot and get tight on the bore...not sure what yours should be.

Nick.

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

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Stoo63
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October 8, 2019 - 10:36 pm
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That's a result for you hopefully, Julian. The rest of the bike is coming on leaps-and-bounds! Great stuff. Nice job with the cellulose. Much prefer that to powder-coating which often doesn't  look quite "right" for the period. But obviously easier and hardy. You'll be up and running in no time, terrorising the back lanes of Devon laugh

Cheers

Stewart

'52 D1 direct lighting plunger; '58 Square Four (project); '55 D3 Battery; '59 D1 direct lighting plunger;  '59 Tiger Cub; '60 5TA;  '76 FS1-E '97 Honda Sky SGX50.

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