Engine a bit flat after rebuilding, this normal?

[simon1221]

As the title, i have just rebuilt my tzr, but when i took it out last night (gingerly), it seems less powerful and struggles up hills below 4000rpm.

I have done everything correctly according to the haynes manual, and there is no real damage to the bore to warrant a rebore.

Will the performance build as it is run in?
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DNA50 (sorry) ->> TZR125l >> GPZ500S

[mr jamez]

Yes, well that is what I found whilst running mine in.

It seemed reluctant to rev, there was little power also. Once I was up to about 8k it felt like it had 'freed' a lot. You may also find that it seems so much slower because you can't use any of the power higher up in the rev range!
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NSR 125F > BROS 400 > NC30 > BROS 400 > Trumpet S4 > '97 VFR 750

[simon1221]

Thanks
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DNA50 (sorry) ->> TZR125l >> GPZ500S

[bish777]

give it a few hundred miles before you start caning it. Take it to the red line now and again to make sure everything beds in but dont do it too much till at least 3 or 4 hundred miles post rebuild.
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GSXR1100J

[gavin]

noooo....

rev it hard! not too hard, but hard enough to make it work. if you potter about at low revs for 100's of miles you will bed the rings in on the honing'nibs' rather than into the bore, you will get less compression, lots of blow-by and this will laquer the piston and cause the rings to gum up, further hampering power. my strokers get run in hard, short hard bursts, not letting it get too hot or running it for too long at a time. last year my tzr on a new piston got just 45 miles on it before it was given full throttle, and the following day it did about 60 milles round llandow circuit in south wales, regularly into the red, with no harm done... took it to bits to check afterwards, no blow by, no gumming,.

whatever you do dont leave it ticking over to 'warm up' when you first start it after a rebuild, just get on it and ride it.

[mr jamez]

[Hijack]

*pokes Gavin

After a complete bottom end rebuild, does it need running in at all? or can I nail it straight away.
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NSR 125F > BROS 400 > NC30 > BROS 400 > Trumpet S4 > '97 VFR 750

[bish777]

smoothley go through the entire rev range but dont rant the bollocks off it!
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GSXR1100J

[gavin]

think about it....running in is about getting different surfaces to bed in with each other, so they run smoothly and dont sieze.


it stems from a time when materials were less advanced, machining was less precise and tolerances were wider. in times passed it was a necesity. i dont think it is now.

provided you have a quality rebuild with quality components, and everything is set up right (oiling, jetting etc) you shouldnt need to treat it with kid gloves.

[bashbashbash]

This is a topic close to my heart. What do you do? In my experience of racing running in is not always easy to do.

Generally after rebuilding the race bike engine I warn the engine up at no more than 3,000 rpm , then I do two warm up laps so about 4 miles with the engine just comming on to cam. This is just to make sure the engine is sweet and the rings have freed up from the oil used to build the engine up.

Now is the worst bit, (bare in mind im on a 2 grand engine) the final two laps of practice I abuse it, redline on the quickshifter but next to no engine braking.

Ive only ever had one let go and that was my own stupid fault, double downshift by mistake.

Anyway this seems to work for me and a lot of guys I race with. I hope it helps.

[the grim reaper]

Bearings like to be run in slowly, pistons like to be run in fast. If you've just had a piston/rebore, cane it, if, as you said, you've had the bottom end done, take it easy. You'll get more power if you run it in hard but the longevity of the new bearings will suffer.

Cheers

Grim
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