The BSA A7-A10 Forum

Technical => A7 & A10 Engine => Topic started by: Colsbeeza on 30.08. 2018 08:02

Title: Rings Matched to Piston
Post by: Colsbeeza on 30.08. 2018 08:02
Well I have the top end stripped down after 40 miles of smoky running-in. The valve guides are very worn and are 90% likely the cause of the smoke. I have also decided to hone the bores, stick in new rings into my nearly-new 25yo Hepolite pistons and dry-run in the new rings. I got a set of GPM (Gandini) rings and as I have begun to learn -  measure everything. Glad I checked.
The Compression rings are reduced in height (thickness) from 1.60mm to 1.55mm compared to the 25yo Hepolite rings. That is about 2 thou. The Groove width (height) is 1.61mm, so all up clearance will be about 3 thou.
The other issue is with the oil rings. Piston Groove depth is 2.80mm. Old ring depth (width) is 2.63mm, giving a clearance of 0.17mm or 6.7 thou. The new oil rings have a depth of 2.85mm. This is greater than the piston groove depth by about 2 thou, or 1 thou on radius. That means that if I stick the new rings in, the oil rings will stick out past the piston by 1 thou. Given the piston - bore clearance of 2 or 3 thou, could I get away with that.?
My options are;- Fit the new rings and risk compression ring clatter and oil ring breakage, fit the old rings, try new Hepolite rings, chase the world for 5 or 6 sets of rings until I strike it lucky with ones that fit, get the grooves machined to suit the Gandini rings, or Give Up.!!
I am inclined to re-fit the old rings. Or should I fit the new rings.?
Col
Title: Re: Rings Matched to Piston
Post by: Peter in Aus on 30.08. 2018 10:22
I would fit the old ones but that just me! *doubt*
Title: Re: Rings Matched to Piston
Post by: BSA_54A10 on 30.08. 2018 14:49
You go to a piston ring maker like Total Seat and order your rings like they should be done
Bore x thickness x radial depth.
Piston & ring makers dumbed down their catalogues to force people to buy what they wanted to sell.
I get mine from Total Seal and have done so for years.
Any ring maker who can only supply rings by engine name & size is not worth dealing with.
Title: Re: Rings Matched to Piston
Post by: Triton Thrasher on 30.08. 2018 18:36
Fitting the new rings that don’t fit is not an option.

Your real options are to try new rings meant for Hepolite pistons or fit new pistons complete with rings.

Re-using old rings in an engine that was smoking sounds like a prelude to another strip down.
Title: Re: Rings Matched to Piston
Post by: Colsbeeza on 31.08. 2018 07:45
Thanks TT,
Yes I have now dismissed the idea of fitting the Gandini rings. Another $96 down the drain. I will ask the dimensions of Hepolite rings, as that is a more likely solution.
Peter, I have not dismissed the idea of using the old-new 40-mile rings, as they look perfect. And I need the thrill practice of tearing down the top end. I also want a second set of rings, as I want to monitor leakdown and change rings when needed in the future.
Trev, I have sent a request to Superperformance in Qld (Total Seal agency) and hope to get a reply.
I might have also found a third source of the smoking LHS cylinder. The gudgeon pins were VERY tight in both the pistons and the little-end bush. I also found the gudgeon pins with hammer-dents on one end (the outside end on each side). Luckily, any obvious damage to the conrods is not yet apparent, but I will be doing some checks there. That also explains the scuffing on the rear of the bores, and the rear of the piston skirts. When I went to remove them, I could not get them to budge by finger, then no budge with a wooden dowel and a light hammer. I had to buy a proper gudgeon pin puller (picture), and it took a couple of ft-lbs force on a 10" ring spanner to wind them out. This was forcing the piston against the rear of the bores on both up and down strokes, not allowing the piston to centre. This also positioned the rings on a slight angle. Who knows what effect this would have on the ring seal! *dunno*, so doubtful about re-using the old rings. Glad I found it after only 40 miles.
There are marks on the gudgeon and the bore of the little-end bushes, but no discernible wear.
I have lightly reamed the bush and pistons back to 0.75" for a firm push fit. A mystery, because when I assembled it 25 years ago, I certainly did not use a hammer. I also found one gudgeon was not uniform, and had to ease one end (the bludgeoned end) with 1200 wet-n-dry (very gently) to get it to fit. Not an ideal solution, but the fit is now nice.
Cheers
Colin
Title: Re: Rings Matched to Piston
Post by: BSA_54A10 on 31.08. 2018 09:13
Good luck with SuperPreformance I gave up on them 20 years ago.
They keep no stock, order your rings in then charge 4 times the catalogue price including freight from the USA to them then freight from them to you .
So you need one of the nice people on this forum to order them for you then post them for  $ 8.00 rather then Super charging you $ 30.

Total Seals catalogue is on line
Measure your bore, measure your grove width then the depth of the grove.
They are then what you search for
Bore in mm width in 1/16th" and depth in 1/10th"
Ask them for +20 A10 Hepolite rings and will tell you they are not available.
http://www.totalseal.com/inquiryform.html
Title: Re: Rings Matched to Piston
Post by: Greybeard on 31.08. 2018 10:35
I meant to post this a while ago. Not wanting to risk damaging my conrods I used a clamp, (plastic faces) to put pressure on the wrist pin then used my hot air gun to warm the piston. After a minute the pin just slid in by using the clamp. I finished the job by using a small socket to push the pin fully home.
Title: Re: Rings Matched to Piston
Post by: Triton Thrasher on 31.08. 2018 12:20
I did not realise that what were called “old rings” had only done 40 miles.

Id still worry that they are damaged from the smoking/stiff gudgeon pin episode.
Title: Re: Rings Matched to Piston
Post by: RichardL on 31.08. 2018 12:24
Fitting the new rings that don’t fit is not an option.

Your real options are to try new rings meant for Hepolite pistons or fit new pistons complete with rings.

Re-using old rings in an engine that was smoking sounds like a prelude to another strip down.

Came across this from Draganfly while looking for  A7 rings:

Ring set for original or Hepolite pistons. This set will fit if the oil ring groove depth is increased by .008” for the +.040” and +.060” sizes. The standard and+.020” sizes do not require any modification STD, 20, 40, 60 (per piston)   A7/ST   1947-50

Ring set for GPM pistons. This set will fit if the compression ring grooves are increased in depth by .010” on standard and +.020” sizes only. STD , 20 , 40 , 60   A7   1947-50

It seems they are being careful about the idiosyncracies of different ring sets in different piston types. Haven't looked up Total Seal yet, but not likely to go with custom rings while doing just a hone and re-ring. I think Trevor might tell me it's worth it anyway.

Richard L.
Title: Re: Rings Matched to Piston
Post by: RichardL on 01.09. 2018 01:13
So, the story of rings has a new twist. Today I went to the Chief Blackhawk Antique Motorcycle Swap Meet in Davenport, Iowa. It is a very big event for all makes, so you can imagine that Harley is the most heavily represented. You would be right. However, it is a pretty amazing display of some very rare bikes amongst a lot of tables and blankets full of junk (to me).

One of the things I was most interested in finding was a set of +40 rings for my barn-find A7. I had little expectation of success. After only about 15 minutes walking around this beast, I came to a stall where the gent sold almost entirely BSA parts. On his table was a carton filled with edge-labeled  boxes of BSA and Triumph rings, dominated by A65. After sorting through for some time I was ready to give up hope, but decided for one more try. Wedged in between the boxes was a lonely unboxed bubble-wrapped package. I opened it and was boosted way up to see "O.H.V. Twin A7 Star A7, 495cc, 50-52", but this was also weird to me. I know longstroke is 47-50, but I expected to see "50-62" for post-longstroke.  *bright idea* *bright idea* These buggers had to have been made in '52! Basically. NOS unobtainium for $25. Wooo hoo! *woo*

Me and the gent selling the rings were both in awe of the packaging and he made me promise to preserve it. I am almost uncomfortable with having to use these rings, but bikes must run.

Richard L.
Title: Re: Rings Matched to Piston
Post by: muskrat on 01.09. 2018 07:36
G'day Richard.
Great find mate.
Think you'll find +20 Rocket Three or T160 will fit for +40 A7. 1/16", 1/16", 1/8".
Cheers
Title: Re: Rings Matched to Piston
Post by: Greybeard on 01.09. 2018 09:10
*
These buggers had to have been made in '52! Basically. NOS unobtainium for $25. Wooo hoo! *woo*
Wow! Amazing find.
Title: Re: Rings Matched to Piston
Post by: Colsbeeza on 03.09. 2018 01:37
Thanks Fellas,
I have been trying to negotiate with Draganfly. They now have only Gandini rings for BSA A10 +020, but will not (as yet) measure them or tell me the dimensions, just keep telling me they are suitable. Don't seem to want to pull them out and measure them, or provide me with any data sheet. So cannot proceed in that direction.
Seems like NOS Hepolite in +020 are hen's teeth, or rocking horse sh--t.!
Yes TT, I'll put off re-installing the old rings for a bit. Now on with getting the head sorted.
Col

Title: Re: Rings Matched to Piston
Post by: RichardL on 03.09. 2018 03:08
Col,

Are you against trusting SRM?

http://www.shop.srmclassicbikes.com/product/a1020-piston-ring-sets-ae-hepworth-uk-made

Richard L
Title: Re: Rings Matched to Piston
Post by: muskrat on 03.09. 2018 09:55
G'day Col.
Not sure what brand these are.
https://tinyurl.com/y7fla499
Over here Classic Allparts list, again not sure of brand.  https://tinyurl.com/y7aonrxg
Cheers
Title: Re: Rings Matched to Piston
Post by: Colsbeeza on 03.09. 2018 14:51
Richard, No. I emailed SRM a few days ago for dimensional details. Their reputation is superb. Awaiting a reply.
Musky - British Austria's are Gandini. The Oil ring depth is 2.85. My Piston Oil ring depth is 2.80mm. I think they are the same as the Gandini rings I got from Classic Allparts.
I am trying to avoid having to machine my piston grooves.
Col
Title: Re: Rings Matched to Piston
Post by: RichardL on 03.09. 2018 16:35
Col,

Maybe I'm confused here (never happened before ;) *whistle*) but it seems to me that if you have 0.004" clearance wall-to-piston (0.002" radially) the 2.85mm-deep Gandini ring will never bottom in the 2.80mm-deep groove. Open to education if I need it.

Richard L
Title: Re: Rings Matched to Piston
Post by: Triton Thrasher on 03.09. 2018 19:32
it seems to me that if you have 0.004" clearance wall-to-piston (0.002" radially) the 2.85mm-deep Gandini ring will never bottom in the 2.80mm-deep groove.

It seems otherwise, to the Hastings Rings people.

https://www.hastingspistonrings.com/tech-tips-faqs/ring-groove-depths-of-piston-rings (https://www.hastingspistonrings.com/tech-tips-faqs/ring-groove-depths-of-piston-rings)

 
Quote from: Hastings
Place the O.D. of the piston ring fully into the piston groove as illustrated.
(https://www.hastingspistonrings.com/files/assets/images/medium/1424367022_check-compression-ring-back-clearance.jpg)

No portion of the inside diameter (I.D.) should protrude beyond the piston land.
Title: Re: Rings Matched to Piston
Post by: RichardL on 03.09. 2018 20:40
OK THEN

Col,

Obviously I was wrong about the clearance. TT has done a service and educated me on the topic. Thanks, TT. Though, I wish they had gone on to describe why there would be damage. I suppose you know why and will describe. 

When working on my bike, I sometimes think of the movie Flight of the Phoenix. In it, the crew of a crashed plane in the Gobi desert must make their aircraft flyable to survive. I guess you could say that if using rings that didn't have enough inside clearance meant you got to fly out of the desert, you'd probably go with 'em.  Col, you're not stuck in the desert, right?

Richard L.
Title: Re: Rings Matched to Piston
Post by: Triton Thrasher on 03.09. 2018 20:59
Thanks, TT. Though, I wish they had gone on to describe why there would be damage. I suppose you know why and will describe. 

I don’t know nuffin.  I’m handing Google over to you now.
Title: Re: Rings Matched to Piston
Post by: muskrat on 04.09. 2018 00:38
G'day Col.
0.05mm = less than 2 thou". If the rings pass the "Hastings" test they'd be OK, as the ring once in the bore is a fair bit bigger OD than the piston meaning the ID is also bigger.
Cheers
Title: Re: Rings Matched to Piston
Post by: RichardL on 04.09. 2018 02:04
Y'y'yahbut, isn't the Hastings test asking for oil ring depth to be 0.015" less than groove depth? The arithmetic I played with had the backside of the oil ring about 0.001" from the groove depth when 0.004" is the piston/bore clearance. Is there something here the Hastings test is not telling us, or I just flat-out don't understand (again)?

Richard L.
Title: Re: Rings Matched to Piston
Post by: Colsbeeza on 04.09. 2018 02:29
That is a great find TT. Explains perfectly. I suspect the damage would occur because the ring may hold the piston off the cylinder wall - doesn't bear thinking about.! Muskrat you're scaring me with the logic - I am wavering.!!
Richard, it is like a desert here - makes everyone desperate. NSW is in 100% drought, We expect 80% of cattle won't survive. One farmer was asked by a city mate what he needed. He said "Bring me some bullets - I've only got 5 left". Oz is running out of hay - truckloads coming from Western Australia and Western Victoria. Newcastle port is trying to figure out how to unload grain - never done that before, always exported. Maybe I should stick in the oversize rings and carry some hay over.
Blow me down - it's raining outside as I type.!!
Anyway, I have ordered the Hepolite rings from SRM - if I have to machine the grooves so be it!.
Col