Running In

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Running In

Postby spookefoote1956 » Fri Jul 13, 2018 7:51 am

How long should a newly bored engine 18/G80 be run in for before giving it a good twonking?
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Re: Running In

Postby ajscomboman » Fri Jul 13, 2018 9:18 am

I have never run an engine in, ever. I've merely worked the engine normally (never more than 3/4 throttle) in all gears for 500 miles before giving it the beans! Covered thousands of miles on all types of bikes and never bust or seized one yet. I believe that if you pussyfoot an engine it takes forever to actually bed in and there is a risk of glazing the bore. Ken De Groome also advised me to do the same with the 2 CS engines he built for me.

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Re: Running In

Postby Rob Harknett » Fri Jul 13, 2018 9:44 am

I'd run it in forever. But I only like to ride my old bikes for enjoyment off main roads and motorways. If I wanted speed there's plenty of bikes more suitable. Also, I would not invite speeding fines. I need my licence more than ever now I'm getting on in years. Walking to my village railway station is exactly a mile. I would find that hard going now I'm getting on in years so would not be able to get out and about. So I would not invite speeding fines and risk loosing my licence. Ken de Groom rebuilt a bottom end for me. When I collected it he said, would you like to bring the barrel along also for me to fit. It was +.060". Ken said it still had plenty of life left in it. He just horned the barrel and fitted new rings. That was about 30 years ago now. I must have done well over 1,000 miles running in the rings. Then one day I dropped down into 3rd to roar up a hill. The piston broke in a thousand bits. There was even bits in the exhaust and carb, every where in the engine. All old bikes now have aged another 30 years since I blew an engine. So take it easy on them.

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Re: Running In

Postby Rob Harknett » Fri Jul 13, 2018 12:00 pm

That is one broken piston in 62 years of riding Rob. I had 32 riding before breaking a piston, and another 30 years since breaking one.

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Re: Running In

Postby clanger9 » Fri Jul 13, 2018 12:51 pm

I'd recommend gradually building up the load on the engine during the running-in period, rather than thinking "Right, I've tootled around for 500 miles, now I can thrash it!".
As Rob found, old engines can sulk if they are suddenly faced with different running to what they are used to...

The idea is to let the engine wear-in to how it'll be used. If you're going to tootle, then tootle. If you're going to thrash it, you'll need to run it in fairly hard, with (occasional, short) blasts of full throttle.

I don't think there's a "magic number" of miles that tell you when an engine is run in. Some modern diesels take tens of thousands of miles to loosen up. My usual rules of thumb for an engine that'll be {ahem} fully used ;) :
1. Just after a rebuild, the engine will be tight. You can tell this from the way it stops suddenly when you kill the ignition. Treat it very gently at this stage (no more than 1/2 revs, 1/2 throttle) until...
2. ...it's loose enough that it spins down naturally when you stop the engine. Now each time you ride it, give it a little more revs for short periods (with light throttle) until it revs freely all the way up to whatever max revs you're happy with. Again, you usually can feel any reluctance/tightness if you give it too much. Usually, this takes a couple of hundred miles.
3. Now build up to full throttle / full revs, giving it a little more for a little longer on each run out. If it's unhappy, it'll splutter/hesitate/tighten so back off immediately if it does any of those. Running the engine slightly rich at this point can be helpful, especially if the engine has been tuned up. You absolutely do not want it running even slightly lean on full throttle, or it'll seize/melt something.
4. At this point (several hundred miles-ish), the engine should be ready for a "good twonk"

On the other hand, there's always the "competition run in". When asked how long it takes to run in one of their engines, the racer's (apocryphal) reply was "By the time it's got round Druids!" :twisted:
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Re: Running In

Postby Rob Harknett » Fri Jul 13, 2018 1:20 pm

Agree with all above. Also never allow the engine to labour. All are different. Unless you know the difference, consider it's a tight engine and will need more running in. Going by a speed limit for X miles is not good if the engine labours, which it could do at 20 MPH. Rob mentioned glazed bore... what about a tight piston that's belted and gets deeply scored / seizes? I have said in this topic before. I must have run in about 15 new cars, lost count. One was really tight. I did about 5,000 miles before I gave it a long run at motorway speed. Up to which I gave short bursts only. The book said 500. All should be considered when running the engine once its warmed up.

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Re: Running In

Postby clanger9 » Fri Jul 13, 2018 2:32 pm

Good points from Rob. Labouring the engine and/or constant high-speed running are both awful for new engines. You're trying to find the happy spot between glazing the bore (too gentle) and seizing the piston (too hard)...

Keep it spinning free across the rev range and all should be well.
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Re: Running In

Postby spookefoote1956 » Fri Jul 13, 2018 4:49 pm

I do hope that no-one has got the wrong idea regarding my question. I have no interest in doing a Burt Munro nor breaking the law and getting fined by the girls and boys in blue. At this moment I am enjoying pootling along at a top speed of 40 and was just enquiring as to opinions relating to as Mr Formby would say "open 'er up a bit".

When she was last rebuilt, 1993, I managed to shear the crank pin during a VMCC roads closed event on the I.O.M and don't want to repeat the episode again in a hurry. There is no intention to thrash her at all but on occasion allow the horses to run a little more.

Hope this clears up the question.
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Re: Running In

Postby Rob Harknett » Fri Jul 13, 2018 8:23 pm

spookefoote1956 wrote:I do hope that no-one has got the wrong idea regarding my question. I have no interest in doing a Burt Munro nor breaking the law and getting fined by the girls and boys in blue. At this moment I am enjoying pootling along at a top speed of 40 and was just enquiring as to opinions relating to as Mr Formby would say "open 'er up a bit".

When she was last rebuilt, 1993, I managed to shear the crank pin during a VMCC roads closed event on the I.O.M and don't want to repeat the episode again in a hurry. There is no intention to thrash her at all but on occasion allow the horses to run a little more.

Hope this clears up the question.

Giving it a good twonking, did not sound very gentle to me. Even a G80 given a good twonking could brake the motorway top speed limit. Perhaps my understanding of the word was a little more than opening up a bit.

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Re: Running In

Postby bob121 » Sat Jul 14, 2018 7:22 am

If it's just a rebore, 50 miles or so should be enough to give it some stick.

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