Do I need new piston rings?

[Kayak23]

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.

https://farm1.staticflickr.com/899/27513616628_1ba44814f1_k.jpgUntitled by Kayak23, 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.

[fatjames]

My non educated guess would be that the measurement once in the cylinder is what's important. I wouldn't worry, but I would wait to see what someone with more experience has to say.

[Kayak23]

Cheers, yeah it's kind of the way I'm thinking given the cost. However, I sure as hell don't want to be stripping this thing down again in a few months!

[chris-red]

If you've gone to the trouble and expense of tearing it apart that far you might as well do as much as you can. I would do the rings.


I'll also just leave this here...

https://tts-performance-parts.myshopify.com/products/suzuki-gsxr400-442cc-je-big-bore-piston-kit
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[Kayak23]

Very nice kit, but it only costs about a £100 than the bike cost me!

[stinkwheel]

I would also only be worrying about the end gap with them in the barrel. Assuming you don't break any putting them back in again, which would make the decision for you.
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[A100man]

+ 1 for re-using existing rings. But I guess it also depends on how much you intend to use the bike. If it's only a summer toy to use for a couple of 1000 a year I say button it up and get on with it . If you're re-building a bike for a 100 mile a day commute then yes get new ones...
Once you've addressed the valve issue bolt it up and check compression and if it seems sensible you've done ok - how many mile on it out of interest..?
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[Kayak23]

It's under 20k, so has done quite a lot of sitting around I suppose.

I chatted with a bloke who works in motor vehicle in the college where I work and he kind of swayed me towards sucking up the cost of new rings considering that I've got it all apart now.

I've ordered them, but, I'm still thinking i could return them if I wanted...

It's a difficult one. It's a lot of money on a not very expensive bike but I love the bike and would love it to be running sweet.

[steve the grease]

Back in the day they used to reckon that 4 thou ring gap per inch of bore for air cooled engines and about half that for water cooled was a rule of thumb that worked.
So 4 thou =0.1mm and an inch is 25.4mm then your ring gaps are about right for a 3inch bore. But like the guy said dont worry too much. Is it blowing out of the breather???

Plus the combustion pressure pushes the rings against the bores , improving compression. It's only done 20k , dont bother.

[rpsmith79]

Funnily enough, i was just watching this the other day

Piston Ring Gap - the importance of:

https://www.youtube.com/watch?v=1-ujH65POaY
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