Stuart Turner R2 Slow Running

For a couple of exhibitions the engine was running progressively slower and finally stopping. i had a look at 'all' the possibilities ie mucky carb, points and plug, timing. Then at the Ellingham Show it would not run fast enough for the alternator (add on) to charge the battery. I removed the head and could not see any exhaust ports, eventually I managed to prod in the right place and broke through a wall of carbon. Unfortunately I didn't take before pics, but this is what it should look like.





Ran at Great Dorset for five days without a hitch

Bernie

Wow that must have been a lot of carbon. Can I ask how long is it since you had the head off? Is it normally smokey when running? Do you use the correct two stroke mix or a little extra oil?

Stu.

We acquired the engineeight years ago and it ran fine for about 500 hours. Mixture is 50:1 but a lot of the time it is guess work with a drop of 2 stroke oil topped up with fuel in a2ltr jug. Memo to self, must purchase a proper 2 Stroke measuring jug. Usually exhaust is as it should be with very little smoke. I guess it was a user problem neglecting maintenance. Remember when we had to top scratch car engines at 50 thousand miles?


Bernie

What 2 stroke oil are you using?
I'm genuinely interested as I was thinking of trying 50:1 in my Stuart but I only use 50:1 with a decent oil like Stihl HP or higher grade.

barneytiffy wrote: Remember when we had to top scratch car engines at 50 thousand miles?

Bernie

Can I ask what this involed doing as I've never heard of it.
Sounds as if everything you've been doing has been ok, just have to put it down to maintanace. Put it on a to do list same as derrhhh I was about to say oil changes well you know what I mean.

Stu.

Ianhw77k wrote:What 2 stroke oil are you using?
I'm genuinely interested as I was thinking of trying 50:1 in my Stuart but I only use 50:1 with a decent oil like Stihl HP or higher grade.

Using proprietary 2Stroke oil from any garage, 50:1 as it says on the fuel tank lid. I often wonder if that's OK with modern oils. Bear in mind that in the days these engines were built it was a mix of leaded petrol and engine oil.

stationary stu wrote:Can I ask what this involed doing as I've never heard of it.
Sounds as if everything you've been doing has been ok, just have to put it down to maintanace. Put it on a to do list same as derrhhh I was about to say oil changes well you know what I mean.

Quite simple, Remove the six head nuts, two secure the exhaust pipe. Ease off the head avoiding damage to the copper asbestos head gasket. the inside of the cylinder is then revealed and with the piston at BDC you should see the exhaust ports on the exhaust pipe side and the transfer ports diametrically opposite.

Bernie

I don't think Stuart Turner tanks would have 50:1 written on them, I thought they were more like 16:1, but if you've had it 8 years & it hasn't seized, then I guess it's fine.

The lead, or rather lack of it, in petrol makes no difference in a 2 stroke. Modern oils mean we can run these old engines on leaner mixes than is stated on their instructions, my Tarpen is supposed to be run on 16:1, but I've always run it on 25:1 & never had any problems. Don't forget, in the old days there wasn't any such thing as 2 stroke oil, it was all engine oil, which doesn't mix as well & was never intended to be burned in an engine. Modern oils are designed for the purpose & work much better. I still think 50:1 is a bit too lean for an older engine though, it just looks like so little when mixing it.

Way back in the early-to-mid 90s I decided to strip down the Tarpen for a rebuild & repaint. The exhaust ports on that were almost completely coked up, they should've been about a square inch each, but both were down to almost an eighth square! Certainly less then a quarter. It was still running fine though, I think they only start to slow down when they are really close to closing up completely, & of course coke attracts more coke & the smaller the gap the quicker it fills up, so it's a process which will speed up as it goes.

It's just an age thing with these old 2 strokes, modern oils will still do it, but not to anywhere near the extent of the old stuff, & that takes decades to coke them up completely.

Scanned this from the manual. It works out at 48:1 so I reckon the cap is the correct one. Seen other R2/R3 with same cap.

Bernie

That's interesting to know, I've got a manual for my P5 so I'll check that out. It would be easier for me to run mine on 50:1 as that's what I use for my tools at work. I'll read the manual properly next time

I stand corrected, I've been talking to a Stuart Turner specialist on line & apparently these old Stuarts were indeed a 50:1 mixture, or roughly the equivalent of. It's got something to do with the use of roller bearings as opposed to plain bronze bushes.

They weren't originally designed to run on leaded petrol either either, apparently, not that it matters with a 2 stroke, as there are no valve seats & oil is added anyway, but I'm told they were originally designed to run on low grade unleaded petrol of the time & will even run on paraffin if got hot enough on petroil mixture first.

I honestly had no idea any of the old British 2 strokes ran on such a lean petroil mix, almost everything else from the UK & USA of the time seems to run on 16:1, from what I know. My little German Auto Union genny engine states 25:1 though, but they were way ahead with 2 stroke design back then (pre war).

P.S. I actually wrote this message before the scan from the manual, I just took hours to post it (too many tabs open), so sorry if it repeats what's been said already.

Ianhw77k wrote: I'll read the manual properly next time

You'll have a job, it's still in my caravan!

Maybe that's why we were having troubles with it. I'm not sure if the P5XC is the same, but I expect it is.

It would be interesting to see if your manual mentions 2 stroke oils, as I'm not sure when they came into being in mainstream garages.

The ports coking up on this one could well be from too strong a mix being used in the past then, & are almost certainly from the use of engine oil instead of proper 2 stroke.

When I restored the Tarpen a few months back I scraped off a reasonable lump of coke from one of the ports, I don't know if it was one which I missed back in the 90s or weather it was newly formed since then. I'm guessing the latter, in which case it happens reasonably rapidly, I would guess that engine had seen about 3-5 years of hard rallying since the rebuild in the 90s, then was stored for over a decade before this summer's restoration.

Do you think that with these engines running at a fixed engine speed just above tick-over this is why they coke up as much?

Stu.

stationary stu wrote:Do you think that with these engines running at a fixed engine speed just above tick-over this is why they coke up as much?

Stu.

That could have something to do with it, but I think it's just an old 2 stroke thing, inherent with the fact they are burning oil & oil doesn't burn very well.

I know a lot of people don't like 2 strokes, but I quite admire their simplicity. I am a bit fed up with them lately as until I got my JAP Model 3 all I had to mess about with was 2 strokes.

I can't remember if we checked the ports on Ian's Stuart P5XC when we put it together, I expect we did, it's usually something I would cast my eye over as I'm assembling, or disassembling, something.

A good friend of the family, a mate of my dad's, is a 2 stroke fan, he used to ride a lot of Villiers 2 stroke engined motorbikes, such as DOT, Francis Barnet, Greeves etc, he often talks of the problems they used to suffer, including coking up of exhaust ports. Mechanics, as a trade, has changed drastically over the past few decades, these days being a car mechanic is more like being a fitter when compared to years ago, as cars become less "user serviceable" & sprout more & more sensors. This is why my dad told me not to pursue it as a career, he was a mechanic & retired in 1998, as more & more cars were simply plugged into a computer which told the mechanic which part to remove & replace. I don't know if they still teach people how to de-coke engines at college, but I think most garages would look at you very funny if you drove in & asked them to de-coke your engine these days! I'm glad there's still places like this where these practises can be re-taught & passed on.

(BTW I'm not having a go at car mechanics, it's the trade in general I'm talking about, I know there are still some very good mechanics about, who know a lot more than just how to fit parts )

Ianhw77k wrote:That's interesting to know, I've got a manual for my P5 so I'll check that out. It would be easier for me to run mine on 50:1 as that's what I use for my tools at work. I'll read the manual properly next time

I went out & got your manuals today (just had to drive somewhere, seeing as I taxed the car yesterday, haven't been able to use it for a week!) & they all say the same, it's a 50:1 mix (or 48:1 if using imperial measures), one of yours is a P4/P5 manual, from 1957, the other is a P5 & P55 manual, from 1961 & the third is a R3 MC & R3 M manual from 1972, they all mention "self mixing 2 stroke oils" & all say the same mixture.

But, it looks like the previous owner has made his own mind up, as he's written next to that paragraph, on one of the manuals, "33:1 or less". He's also marked up next to "Starting Problems" & various "Troubles" sections, so he was obviously having issues with the engine.

Still, I'm pleased to know I won't have to share my Tarpen fuel with it, but not so pleased to know we now need 3 different types of 2 stroke mix for the 3 different 2 stroke machines we are to be running next season. I'm told the Homelite will only run on 16:1 with SAE 30 oil, my Tarpen is only happy at 25:1 with basic 2 stroke oil & the Stuart now wants 50:1! We're going to need more petrol cans! Either that or sell them all & get more 4 strokers!

I use 50:1 for work, although it is a bit expensive. I also have a spare can I can use for the Stuart and I buy another 2 stroke oil (semi synthetic 50:1 red one) to stick in my diesel for my car so we do have many options.

Always good to learn something new, thanks to the original poster for bringing it to my attention

Do you think the coking up of two stroke stationaries could be down to over cooling due to large water cooling tanks?

billypurves wrote: Do you think the coking up of two stroke stationaries could be down to over cooling due to large water cooling tanks?

Blimey, now there's a thought. My Tarpen is air cooled, so that's not the issue with that, although it may well still be over cooled, it has an engine driven fan, driven by a V belt at well over engine speed (I know the pulley on the engine end is 5 inch, the one on the fan end must be somewhere between 2 & 3 inches diameter).

I suppose it all depends on how it's cooled, I know my brother's P5XC is thermo-syphon cooling, which in theory should find it's own level, but a pumped system is different.

I did notice, in one of the Stuart Turner manuals I flicked through earlier today, they spoke of adding bricks to large cooling tanks to reduce the amount of cooling water, thus increasing running temperature, if you wanted to run the engine on paraffin (BTW, anyone wanting to do this, you still need to add the same ratio of oil to the paraffin as you would petrol).

I will ask around in the next few days, I'm off to Goodwood on Friday for the Revival practise day & I'm at a rally all weekend (last of the season for me) so I'm bound to get some different answers & ideas there. I would like to know how the coking is made worse, if only to try & make it better, but I don't think it's avoidable altogether.

At one time I was mad on CS diesels. All I used for a cooling tank was a fire extinguisher to get some heat into the engine to avoid what the Americans call "slobber" that oily, carbony,sooty horrible watery gungy stuff that creept out of the exhaust if they were over cooled.

Engines run better anyway with a bit of heat about them....as long it is not too much ....over cooling wise.