Do I need new piston rings? Motorcycle content

Hi.

I’m currently in the process of rebuilding the top end of my 1982 GSX400F. It needs the valves doing etc.

I also have the head off as I’m painting it etc.

I’ve cleaned all the coke off my pistons and am now turning my attention to the rings.
All of the bores are nice and smooth, no scoring however, they don’t have the cross hatching from a fresh hone.

Before I dismantled the engine I did a leakdown test, and found the valves were not sealing, hence the teardown. I found that leakage to the oil filler (indicating worn rings) wasn’t too bad but it was there(bearing in mind it’s a cold engine obvs)

I’ve been looking at how you measure the rings properly and they all seem to be within wear tolerances except for ‘free end gap’ limits.
I can’t actually find anyone really mentioning this measurement as important, other than in my manual so am wondering how much weight I give it considering that the end gaps when in the cylinder are all good and replacing all 4 sets of rings will set me back about £190.

Untitled by Kayak23[/url], on Flickr

Measurements are as follows…

Cylinder 1
1st ring
Free end gap = 6.4mm
In Cyl gap = .406
2nd Ring
Free end gap = 7.76
In Cyl gap = .305

Cylinder 2
1st ring
Free end gap = 5.79mm
In Cyl gap = .406
2nd Ring
Free end gap = 7.95
In Cyl gap = .381

Cylinder 3
1st ring
Free end gap = 6.38mm
In Cyl gap = .406
2nd Ring
Free end gap = 8.38
In Cyl gap = .330

Cylinder 4
1st ring
Free end gap = 6.35mm
In Cyl gap = .406
2nd Ring
Free end gap = 8.35
In Cyl gap = .305

So, all of the rings are seemingly well within the end gap limit when inserted into the cylinders, but, most of them are over the limit when free.

Is it advisable to get new rings anyway, and if so, anyone know a good place to try to get them that might come out a little easier on the wallet!?

Cheers.

https://www.therevcounter.co.uk/forums/13-The-Motorbike-Mechanics

Depends how flush you’re feeling. If you’ve stripped the engine down I’d probably splash the cash on new rings. You’ll be properly annoyed if your newly rebuilt engine smokes. Your call, sorry not much help am I,

If you swap the rings you’d be best to hone the bores at the same time as if there are no honing marks visible its likely the bores are very polished so the new rings will never seal.

I’d also be measuring to make sure the bores are round and within spec.

If it was me and I’d gone as far as getting the rings out to measure I’d swap them as a matter of course.

As above.

I think I’d either use the original rings due to the glazed/smooth bores, or rehone/glazebust the bores and new rings.

Is there any step at the top of the bore?

Depends on the useage of the bike once done.

Pfft if the pistons are out why not a rebore and bigger pistons?😎

If you’ve stripped the engine down I’d probably splash the cash on new rings. You’ll be properly annoyed if your newly rebuilt engine smokes.

I will. I’ll be devastated. However, it was fine before, no smoking. The only reason I’ve torn it down is because a leakdown test was showing leaking valves and once I got in there and saw all the coke on the pistons I thought sod it, I’ll clean them up, and once in there I thought sod it, I’ll paint the engine…. you know the score. 🙂

If you swap the rings you’d be best to hone the bores at the same time as if there are no honing marks visible its likely the bores are very polished so the new rings will never seal.

I’d also be measuring to make sure the bores are round and within spec.

If it was me and I’d gone as far as getting the rings out to measure I’d swap them as a matter of course.

I have a bore honing tool. Bit scared to use it if I’m honest…

I had all the bores measured yesterday. The college where I work has a motor vehicle dept and they used one of them fancy probe things that measures things incredibly accurately All bores were within the limits in the manual.

I would like to swap the rings but, it’s the cost. To be honest I hadn’t thought they’d cost me the best part of 200 notes!

As above.

I think I’d either use the original rings due to the glazed/smooth bores, or rehone/glazebust the bores and new rings.

Is there any step at the top of the bore?

Depends on the usage of the bike once done.

Doesn’t seem to be any step. Feels pretty smooth to me.

Bike isn’t a commuter or anything. It’s just a leisure thing.

If it’s all apart anyway I’d hone it and fit new rings. No idea of the quality or if they’re right for your model but just googling GSX400F piston rings comes up with sets for about £25.

If it were me I’d just have taken the head off and re ground the valves, if the leakdown test was fine and the valves were definitely leaking then taking the pistons out was always just going to make more work for yourself!

If it’s all apart anyway I’d hone it and fit new rings. No idea of the quality or if they’re right for your model but just googling GSX400F piston rings comes up with sets for about £25.

If it were me I’d just have taken the head off and re ground the valves, if the leakdown test was fine and the valves were definitely leaking then taking the pistons out was always just going to make more work for yourself!

Yeah I’ve seen those, but £25 from China is too much gamble for me I think. Could do a lot of damage if they fail I reckon.

The leakdown test was fine-ish. I mean, I could hear air escaping through the oil filler, which was worse on one cylinder but it wasn’t excessive. Reading up on test results though did suggest that they may be leaking slightly with those symptoms.

I wondered whether this could be due to them being all coked up. Now its all clean I’m not so sure they need replacing but perhaps I should just go with the painfully expensive option.

It smarts a bit to have to spend a third of what the bike cost me on piddly little ringy things is all.. 🙂

If you hadn’t had the engine apart you’d have never thought about changing them. I mean, there’s a small risk that now everything is clean and disturbed it’ll pick up some issue but if you get the same condition back as you had before then you’ll be happy I reckon.

Dry rings will pass when you do a leak down unless you drop a bit of thick oil in first to seal the gaps and differentiate between valves or rings.

Honing obviously involves crank out – if you’re at that stage you might as well de glaze/rebore and new piston&rings.

I would just put the rings back in, head on and ride it.

Ring blow by isn’t a massive problem providing there is still enough compression left in the cylinder for the thing to work!

You can always drill a small hole in the filler plug to elviate any crankcase pressure.

I recently did the rings on my gsxr1100 after a low compression test result and a leak down test showing leaking valves, I got the rings from partzilla in the US, even after shipping, VAT and duty they were still almost half the price of buying from the UK and they were genuine Suzuki.

When I measured the ring gaps in the cylinders they were all either out of spec or very close to the top end, you could still see the honing marks in the cylinders, so I was advised just to put in new rings and not have it honed.

To be honest in your case with the ring gaps being OK and the cylinders looking good, I would probably just rebuild it with the original rings and lap the valves in to get them sealing properly.

I think the idea of the free end gap is to ensure that the piston rings don’t exert too much pressure on the cylinder bores and cause premature wear. Doesn’t seem to have been an issue so far if everything else is within tolerance

Personally, I’d replace them for a longer-term gain

If you like the bike and intend to keep it get new rings. Or get it bored out and new rings with some fancy pistons to go in them

Your ring gaps look fine to me. The fact that your free ring gaps are “over” as you put it is a good thing and is proof that the rings are capable of exerting adequate tension on the cylinder bores. If they were under by a significant margin then yes they would need replaced.

The in bore gaps also well inside the service limit. I personally don’t like running engines with ring gaps massively inside the in-bore measurement, especially on an air cooled engine that’s been built to produce maximum power. When hot or overheated the gap can close completely causing butting. This will lead to a seizure of varying magnitude depending how quickly it’s noticed.

If this were mine, I’d clean everything including the ring lands and check for any cracks on the pistons. You don’t want any deposits on the ring land area as this can prevent the ring’s free movement. Make sure the piston rings are intact with no bits chipped off the ends & can move freely once in their grooves. Lubricate during re-assembly.

You’ll get conflicting advice on what to do with the bores. If they’re glazed and properly polished they’ll need deglazed. If you’ve had a piston/bore sealing problem you’ll be able to see witness marks (blowby) on the piston skirts. It’ll be obvious, not to be confused with a little discolouration which is entirely normal. Glazing is different to normal wear.

Glaze-busting is best done with a proper glaze busting tool. Not one of the one’s with three stones which are the devils spawn. It can be done adequately by hand using sandpaper to produce a fine crosshatched finish. I tend to avoid carborundum based paper as particles can become lodged in the cylinder wall. I don’t know if that’s an old wives tale, but something I don’t do.

You did a leakdown test. Did you do this twice with a 2nd set of reading after putting oil down the bores. Were the figures different?

Have you checked the piston clearances?

D.

Dismantling them was your problem.
How much do the ring gaps vary at different points down the bore?
That is the real measurement of how worn things are, as if the gaps are noticeably bigger near their TDC position, compared to further down the bore, then that means the bore is worn.

Now you’ve disturbed everything, it can be a bit of a gamble as to how well things will work if you do put them back together. Rings/bores wear into each other, so even parts worn well outwith tolerances can still work well and give no problems, but partially worn parts within tolerances when reassembled can cause problems.

Personally, I’d re-assemble as is, and see how it goes.

I’ve never understood peoples fascination with glaze breaking when rebuilding with the same parts, as all you’re doing is accelerating wear as the parts then need to wear/bed in to each other again. And if the bore is worn enough to of worn through the previous honing, then at best glaze breaking is a bodge.

If you hadn’t had the engine apart you’d have never thought about changing them. I mean, there’s a small risk that now everything is clean and disturbed it’ll pick up some issue but if you get the same condition back as you had before then you’ll be happy I reckon.

True, although the reason I decided to delve deeper originally was partly because I had ongoing running issues, difficult starting at times but mostly an erratic idle was the biggest issue. Also, fairly sluggish, though that could just be because it’s only a 400cc obvs. 🙂

My original compression readings were showing this, tried dry and then with a teaspoon of engine oil;

Cylinder 1 – 50psi Dry, 50 wet

Cylinder 2 – 100psi Dry, 105 wet

Cylinder 3 – 100psi Dry, 125 wet

Cylinder 4 – 100psi Dry, 125 wet

Then I did leakdown tests (Though I didn’t actually do this with oil added, only dry)

Cylinder 1 – Air escape from exhaust a fair bit, tiny bit from airbox and oil filler

Cylinder 2 – Exhaust ok, airbox ok, air coming from fuel inlet pipe on carb, little from oil filler

Cylinder 3 – Exhaust ok, airbox…meh, oil filler a little

Cylinder 4 – Exhaust ok, airbox escaping, oil filler escaping.

Dry rings will pass when you do a leak down unless you drop a bit of thick oil in first to seal the gaps and differentiate between valves or rings.

I didn’t know adding oil was part of a leakdown actually, I thought just compression.

Ring blow by isn’t a massive problem providing there is still enough compression left in the cylinder for the thing to work!

Yeah, hopefully now I’ve done the valves the compression will improve a lot. How much this lack of compression was down to the rings i’m unsure of now.

I recently did the rings on my gsxr1100 after a low compression test result and a leak down test showing leaking valves, I got the rings from partzilla in the US, even after shipping, VAT and duty they were still almost half the price of buying from the UK and they were genuine Suzuki.

I looked at Partzilla, but they don’t list my bike sadly. It’s an older bike but not really a classic as such and so seemingly aftermarket and presumably genuine parts are less available.

To be honest in your case with the ring gaps being OK and the cylinders looking good, I would probably just rebuild it with the original rings and lap the valves in to get them sealing properly.

Hmmm, I’m still torn… :-/

I think the idea of the free end gap is to ensure that the piston rings don’t exert too much pressure on the cylinder bores and cause premature wear. Doesn’t seem to have been an issue so far if everything else is within tolerance

Personally, I’d replace them for a longer-term gain

Makes sense. I’m erring towards replacing them to be on the safe side I reckon.

If you like the bike and intend to keep it get new rings. Or get it bored out and new rings with some fancy pistons to go in them

I do like the bike. I’m slowly going to overhaul and customise it so I do plan on keeping it for the foreseeable. Not sure how much a rebore and new pistons/rings would be but sounds pricey. Someone on a bike forum already linked to a piston kit which gave you something like 44cc more capacity. I’m not racing or owt, just pootling so I’m not really sure I want to go down that road.

If this were mine, I’d clean everything including the ring lands and check for any cracks on the pistons. You don’t want any deposits on the ring land area as this can prevent the ring’s free movement. Make sure the piston rings are intact with no bits chipped off the ends & can move freely once in their grooves. Lubricate during re-assembly.

No evidence of ‘blow-by’ as far as I can tell. I mean they have now been cleaned a fair bit but all the piston sides look pretty uniform in texture, colour and glaze etc. Pistons all going in the ultrasonic cleaner again today as now I’ve removed the rings I can still see some carbon in the grooves.

Untitled by Kayak23[/url], on Flickr

Glaze-busting is best done with a proper glaze busting tool. Not one of the one’s with three stones which are the devils spawn. It can be done adequately by hand using sandpaper to produce a fine crosshatched finish. I tend to avoid carborundum based paper as particles can become lodged in the cylinder wall. I don’t know if that’s an old wives tale, but something I don’t do

Oh…The three-stoned one is exactly what I got in readiness… :-/

You did a leakdown test. Did you do this twice with a 2nd set of reading after putting oil down the bores

No, only the compression test with the oil.

Have you checked the piston clearances?

Not checked the clearances with the pistons inserted but the pistons themselves are well within tolerance, as are the bores.

Dismantling them was your problem.
How much do the ring gaps vary at different points down the bore?

They are the same at the top of the bore and a piston length down the bore.

Thanks for all the help folks. Still not totally decided what to do with it. I’ve actually ordered the rings but am still deciding whether they’ll get sent back or not though I have to say, I’m erring towards just saying bugger it and fitting the new ones so there’s no doubt. I take it I need to hone the bores then if I do this?

Cheers.

<span style=”display: inline !important; float: none; background-color: transparent; color: #222222; font-family: ‘Open Sans’; font-size: 16px; font-style: normal; font-variant: normal; font-weight: 400; letter-spacing: normal; line-height: 22.4px; orphans: 2; text-align: left; text-decoration: none; text-indent: 0px; text-transform: none; -webkit-text-stroke-width: 0px; white-space: normal; word-spacing: 0px;”>They are the same at the top of the bore and a piston length down the bore.</span>

Define ‘top of the bore’.

The highest wear point on the bore is where the ring is at just before TDC, as that is where the ring has the most force applied to it. A measurement should be done there, then either above that if the bore is clean, or at the bottom of the bore.

If you do fit new rings, then yes, you will have to hone/glaze break the bores. Otherwise the new rings will take far longer to bed in. The three stone hones are OK for a quick glaze break, but the problem with them is they’ll make any out of round areas in the bores worse.

Top of the bore as in I took the top ring off, inserted it into the bore and used the upturned piston to ‘square’ it. So the distance from the top of the piston to the second ring, if that makes sense.

In terms of ‘glazing’ of the cylinder and the ‘roughing’ up of the cylinder, I’m getting a lot of conflicting cases for and against it once you search around t’internet a bit. Just read an article which is fairly convincing against it. Not sure what to do yet.

http://bikesandtravels.com/biker.aspx?ride=842

Then this…

.http://www.snowvalley.20m.com/bikes/dnthone.htm

That second article highlights the pitfalls of honing, but what it doesn’t mention is durability.
Those scratches are what helps keep things lubricated, which helps improve lifespan.

However the key thing to notice, is regardless of the approach you take, you get a period of accelerated wear, which is why I made my initial comment about dismantling being your problem.
Everything you have would of been bedded in nicely, but now even if you reassemble them, unless you can guarantee the rings go back in the exact same position they came of, things are going to wear faster until they settle in again. However they are more likely to wear in quicker and less than fitting new rings.

Do you know what the compression reading should be for that engine?  Even your wet ones look very low to me, I’d be expecting 170 plus.

Yeah, all the readings were very low. Amazing the bike still worked!

That’s why I then did a leakdown, and then decided on a valve job. Everything after that kind of evolved. In fact, yesterday, just looking at the sorry lump left in the frame, I took the rest of the engine out and set about painting it. 🙂

Untitled by kayak23[/url], on Flickr

<span style=”text-decoration: underline;”>Untitled by kayak23[/url], on Flickr</span>

Untitled by kayak23[/url], on Flickr

Untitled by kayak23[/url], on Flickr

Holy carp it started first go! 😁

Very pleased with that. I let it warm up and then took it for about a ten mile run at various speeds.

I’m reading lots of different ideas about running new rings in. Anyone here have any thoughts on it?

Incidentally, the old issue I always had with an erratic idle seems to still be present 😢

All painted up niceUntitled by kayak23[/url], on Flickr

All back togetherUntitled by kayak23[/url], on Flickr

Excellent.

Like your choice of mirrors

Ride it like you stole it if you want max power (at the debatable expense of engine life).  Be too gentle with it and the rings might not bed in well.

I think I’ll go medium stole it. Rather it lasted.

It’s not a fast bike 😁

Nice work.

the old issue I always had with an erratic idle seems to still be present

Have you balanced the carbs?

No, I do plan to do that but everything went back as it came out.

The intake boots look fine and new o-rings so I’m pretty sure there’s no leak there. It’s kind of annoying to be honest. I had thought this rebuild would rid me of these issues I had 😓