Little/big end play
Discussion
Really depends on the engine in question but generally, no perceptible play.
If its your Lotus engine then definitely, no perceptible play.
The only real way to check tolerances (unless you whip the big end caps off and find knackered shells!), is to plastigauge the bearings and check the clearances.
What was the nature of the tapping noise? At all revs? Heavy or light knocking?
If its your Lotus engine then definitely, no perceptible play.
The only real way to check tolerances (unless you whip the big end caps off and find knackered shells!), is to plastigauge the bearings and check the clearances.
What was the nature of the tapping noise? At all revs? Heavy or light knocking?
No's my Honda Xr250r, bought it last month and has been fine until a 60 mile trip on Tuesday. Ever since then there's been a loose tappet type noise at all revs.
Here's a video of the play
http://www.youtube.com/watch?v=Znwj3lLy_Zw
Here's a video of the play
http://www.youtube.com/watch?v=Znwj3lLy_Zw
Edited by Flipatron on Sunday 20th September 15:45
Totally shagged. Little end play in a floating bush should be about half a thou which means the rock on the pin will be at most a few times that. Yours has maybe 20 to 40 thou rock which means 5 to 10 thou wear. I doubt the rest of the engine is useable if the little end has gone that badly. They are usually the last thing to show problems.
BTW there's an engineering formula to calculate the wear in a bushing from the rock on the pin as measured with a dial gauge.
Here's what you do. Take the pin and insert it into the bushing until the far end of the pin is just flush with the far end of the bushing. Easiest done if you put the conrod or whatever it is onto a flat surface and insert the pin until it bottoms out.
You then need to put a dial gauge on the other end of the pin and measure the total rock from side to side.
You then need only 3 measurements.
1) Length of bushing (B)
2) Length of pin (P)
3) Rock at end of pin (R)
The clearance (C) between the pin and bushing is then calculated as RxB/2P-B
So for instance we have a pin 50mm long in a bushing 15mm long and the rock is 40 thou.
Clearance is 40x15/100-15 thou
= 7.06 thou
Here's what you do. Take the pin and insert it into the bushing until the far end of the pin is just flush with the far end of the bushing. Easiest done if you put the conrod or whatever it is onto a flat surface and insert the pin until it bottoms out.
You then need to put a dial gauge on the other end of the pin and measure the total rock from side to side.
You then need only 3 measurements.
1) Length of bushing (B)
2) Length of pin (P)
3) Rock at end of pin (R)
The clearance (C) between the pin and bushing is then calculated as RxB/2P-B
So for instance we have a pin 50mm long in a bushing 15mm long and the rock is 40 thou.
Clearance is 40x15/100-15 thou
= 7.06 thou
Edited by Pumaracing on Monday 21st September 09:25
That's useful equation but I doubt you'd need to use it on a car engine. Would you use it for suspension bushings on trucks, king pin wear etc? I'll save it though in case I need it for something bigger. As you said, you'd never want that much clearance in a con rod bush. You only want .005" or a tiny bit more and if you can feel slack or see wear then it's shagged.
It's an equation I actually use very often on car engines for such things as valve to guide clearance as well as gudgeon pin clearance. In fact you use it anywhere it's easier to measure rock with a dial gauge than the actual bore diameter. I've got it set up in a spreadsheet so I can enter either the rock or the clearance and obtain the other desired value.
It also has the advantage it magnifies the measurements considerably so you get a more accurate result than trying to measure both the pin and the bore and subtracting one from the other.
The magnification is given by the rock factor 2P-B/B so in the example above every 1 thou of clearance gives 2x50-15/15 = 5.67 thou of rock at the end of the pin. You'd have to be able to measure the pin and bore to very high levels of accuracy to compete with a quick check with a dial gauge like this and with very small diameter things like valve guides you ain't gonna have a bore gauge that small anyway because they don't come that small. You have to use go/no-go gauges. I think the smallest dial gauge bore comparator I have goes down to 3/4". Below that I can use an expanding split ball gauge down to about 3/8" I think it is and for anything else it's a matter of turning something up on the lathe and seeing if it fits down the hole.
With the rock method as long as you've got any decent straight accurately ground length of bar that'll fit down the hole you can obtain a good measurement of the bore size just with your dial gauge. In most cases of course you already have the valve or gudgeon pin or whatever it is that fits in the bore anyway to use like this.
It also has the advantage it magnifies the measurements considerably so you get a more accurate result than trying to measure both the pin and the bore and subtracting one from the other.
The magnification is given by the rock factor 2P-B/B so in the example above every 1 thou of clearance gives 2x50-15/15 = 5.67 thou of rock at the end of the pin. You'd have to be able to measure the pin and bore to very high levels of accuracy to compete with a quick check with a dial gauge like this and with very small diameter things like valve guides you ain't gonna have a bore gauge that small anyway because they don't come that small. You have to use go/no-go gauges. I think the smallest dial gauge bore comparator I have goes down to 3/4". Below that I can use an expanding split ball gauge down to about 3/8" I think it is and for anything else it's a matter of turning something up on the lathe and seeing if it fits down the hole.
With the rock method as long as you've got any decent straight accurately ground length of bar that'll fit down the hole you can obtain a good measurement of the bore size just with your dial gauge. In most cases of course you already have the valve or gudgeon pin or whatever it is that fits in the bore anyway to use like this.
Edited by Pumaracing on Monday 21st September 09:23
Flipatron said:
That's the funny thing, the valve gear, rockers and camshaft are in A1 condition?
I suppose it's possible this particular engine has a design weakness in the little end but it's incredibly rare to see bad little end wear in modern engines, at least until such mileage as the rest is totally knackered anyway. Maybe the grade of bronze in the bush was wrong (vanishingly unlikely) or there was a manufacturing fault on that particular rod but I'd check everything else in the engine very carefully.Little ends need very little oil, just whatever splashes up off the crank is enough so usually the crank bearings have gone long before the little end does. I can't even remember ever seeing a really shagged little end bush in 30 years of doing this. Maybe the odd one with an extra half a thou or a thou wear that was still running ok but nothing close to what yours is like.
It's not hard to get the rod rebushed btw if that's all that's needed. Any custom rod manufacturer or some of the bigger engine reconditioners should be able to press out the old bush, slap a new bit of bronze in and hone it to size. A mate of mine has a Sunnen rod honing machine for such jobs if you're in the UK.
I don't have any specific experience of the XR250, but all the modern 4 stroke Jap bike engines I have worked on have conventional oil-fed plain journal cranks. Roller bearing cranks are limited to 2 strokes these days. Roller bearing engines are bulky and heavy compared to plain journal type, hence the move away from them.
In that case the rod will be a normal type with a big end cap secured by studs/nuts. Most often, the little ends are not bushed and the pin runs direct in the steel of the rod. I have found this to be a weakness in the past. e.g. my CBR600 race bike was always having the gudgeon pin picking up in the rod. You can just buy a new rod, or there might be enough meat in the little end to have an engineer fit a thin wall bronze bush. If your XR250 rod does have a bush as standard, it will make the job more economical.
In that case the rod will be a normal type with a big end cap secured by studs/nuts. Most often, the little ends are not bushed and the pin runs direct in the steel of the rod. I have found this to be a weakness in the past. e.g. my CBR600 race bike was always having the gudgeon pin picking up in the rod. You can just buy a new rod, or there might be enough meat in the little end to have an engineer fit a thin wall bronze bush. If your XR250 rod does have a bush as standard, it will make the job more economical.
Flipatron said:
I don't think It's bushed, just runs in the steel. I'll try a new gudgeon pin first, see how much play I get.
So you intend to ignore the good advice you've already had from every person who's posted including myself a race engine builder of high repute and 30 years experience that from the evidence of your video your little end bush is completely shagged beyond any hope of re-use and beyond anything in fact I've even seen in 30 years of doing this?Makes me wonder why I bother. It was certainly a waste of my time in this instance.
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