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| Point bounce? https://www.ausmini.com/forums/viewtopic.php?f=2&t=53193 |
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| Author: | Austin850 [ Wed May 13, 2009 3:39 pm ] |
| Post subject: | Point bounce? |
Hi, I'm getting what feels like valve bounce at around 5,000 rpm (just by ear as my new tacho doesn't arrive until next week). Is it possible that it could be point bounce? Does this feel the same as valve bounce? The points are pretty old and probably due for replacement anyway. Cheers, Simon |
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| Author: | TheMiniMan [ Wed May 13, 2009 3:43 pm ] |
| Post subject: | |
Vlave bounce is a mechanical rash noise,,, it`s a yukky sound (yes "Rash & Yukky" are both technical terms)  too soft valve springs will cause this,,,, or too big a cam profile for the springs used will do the same thing
POints bounce would only happen if you`re all set up perfectly & running past 8000rpms with std (Non-"S") points,,, or you`re not set up well & with too big a points gap it may start a bit earlier but you won`t hear any mechanical rash noise , it may just miss & fart |
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| Author: | Austin850 [ Wed May 13, 2009 3:52 pm ] |
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Thanks Matt. I'll look at the valves then. I'll talk to the mob who rebuilt my head last year (I've only had the car on the road a while so haven't driven it in anger much). They put new springs in and I don't know what they used. I'll wait until I get the new tacho in and see things are going wrong and then have a chat to them. Cheers, Simon |
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| Author: | 89Mayfair [ Wed May 13, 2009 7:01 pm ] |
| Post subject: | |
Never had it happen on our Mini but have experienced it in my Valiant. The points would start to bounce/float at around 5000rpm and it felt kind of like a rev limiter that the modern cars have. The engine would start missing like crazy. A lot of play in the dizzy and a sad set of points didn't help. Replaced it with a new electronic dizzy and problem was solved. |
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| Author: | drmini in aust [ Wed May 13, 2009 7:06 pm ] |
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Early dizzys with the old square cam suffered points bounce, well before 7000. That's why an an S has 32oz points, also why later dizzys got an assymetric cam. 
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| Author: | Tadhg [ Wed May 13, 2009 7:14 pm ] |
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Simon, you're saying 5,000rpm, can you give us a speed/gear/diff ratio? That way someone on here will be able to confirm your revs.
I've never had points bounce, but I have had valve bounce. I'm sure it was valve bounce - 29mph in 1st was fine, but 30mph... Loud, harsh, fluttering sound. Just a bog stock 1100, rod change (assumed 3.765 diff)... So it had every right to suffer valve bounce at reasonable rpm.  Simple solution for me back then (this is years ago, different car to present) - don't try and run past 28mph in first gear!
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| Author: | drmini in aust [ Wed May 13, 2009 7:18 pm ] |
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Rodchange never had a 3.765 in it, every one I've stripped has been a 3.44.
The 1098 Mini K/Clubby 1100s with remote box were 3.647:1. |
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| Author: | LS1380 [ Wed May 13, 2009 9:00 pm ] |
| Post subject: | |
We always used GL568 Points...but if you can them now,they cost appox $40.00 set 
I've got a couple of sets sitting in the top draw,as I now run on electronic setup. |
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| Author: | 9YaTaH [ Wed May 13, 2009 9:15 pm ] |
| Post subject: | |
Tadhg wrote: Simon, you're saying 5,000rpm, can you give us a speed/gear/diff ratio? That way someone on here will be able to confirm your revs.
I've never had points bounce, but I have had valve bounce. I'm sure it was valve bounce - 29mph in 1st was fine, but 30mph... Loud, harsh, fluttering sound. Just a bog stock 1100, rod change (assumed 3.765 diff)... So it had every right to suffer valve bounce at reasonable rpm. Simple solution for me back then (this is years ago, different car to present) - don't try and run past 28mph in first gear! Simon...you shouldn't be getting valve bounce at 5000 either...unless the springs are weak...do you have a different cam profile or something?? 
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| Author: | Austin850 [ Thu May 14, 2009 12:00 am ] |
| Post subject: | |
9YaTaH wrote: Tadhg wrote: Simon, you're saying 5,000rpm, can you give us a speed/gear/diff ratio? That way someone on here will be able to confirm your revs. I've never had points bounce, but I have had valve bounce. I'm sure it was valve bounce - 29mph in 1st was fine, but 30mph... Loud, harsh, fluttering sound. Just a bog stock 1100, rod change (assumed 3.765 diff)... So it had every right to suffer valve bounce at reasonable rpm. Simple solution for me back then (this is years ago, different car to present) - don't try and run past 28mph in first gear! Simon...you shouldn't be getting valve bounce at 5000 either...unless the springs are weak...do you have a different cam profile or something?? I've got the same cam that I've had in the car since the mid nineties. I've had it up to over 7,200 rpm at that time but the engine sat for a very long time while I bought houses and had kids etc. I had the head de-cracked and unleaded last year and at the same time they recommended replacing the valve springs. The place where I had the work done know Minis well and should have hopefully put reasonable springs in. The points are the same ones which I had in the car 15 years ago so I thought that they might be a bit dodgy (just hoping for an easy fix). When I get my tacho (it's in Sydney according to UPS tracking) then I'll try and work out exactly what's happening when. Thanks for your suggestions. Cheers, Simon |
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| Author: | 9YaTaH [ Thu May 14, 2009 7:09 am ] |
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Austin850 wrote: 9YaTaH wrote: Tadhg wrote: Simon, you're saying 5,000rpm, can you give us a speed/gear/diff ratio? That way someone on here will be able to confirm your revs. I've never had points bounce, but I have had valve bounce. I'm sure it was valve bounce - 29mph in 1st was fine, but 30mph... Loud, harsh, fluttering sound. Just a bog stock 1100, rod change (assumed 3.765 diff)... So it had every right to suffer valve bounce at reasonable rpm. Simple solution for me back then (this is years ago, different car to present) - don't try and run past 28mph in first gear! Simon...you shouldn't be getting valve bounce at 5000 either...unless the springs are weak...do you have a different cam profile or something?? I've got the same cam that I've had in the car since the mid nineties. I've had it up to over 7,200 rpm at that time but the engine sat for a very long time while I bought houses and had kids etc. I had the head de-cracked and unleaded last year and at the same time they recommended replacing the valve springs. The place where I had the work done know Minis well and should have hopefully put reasonable springs in. The points are the same ones which I had in the car 15 years ago so I thought that they might be a bit dodgy (just hoping for an easy fix). When I get my tacho (it's in Sydney according to UPS tracking) then I'll try and work out exactly what's happening when. Thanks for your suggestions. Cheers, Simon Hmmmm I'd be looking for a broken valve spring possibly....good luck
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| Author: | Morris 1100 [ Thu May 14, 2009 6:10 pm ] |
| Post subject: | |
If a motor has sat for a long while it will have had a couple of valves open. Those springs can be weak from the stress of sittng under load. Pull the rocker cover and try to press open each valve with your thumb. If one is weak it will open easier (or it will open when you can't open the others) |
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| Author: | Austin850 [ Thu May 14, 2009 6:44 pm ] |
| Post subject: | |
Thanks Morris, The springs were all replaced when I had the head reconditioned last year so they should all be good. Cheers, Simon |
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| Author: | 9YaTaH [ Thu May 14, 2009 7:12 pm ] |
| Post subject: | |
Austin850 wrote: Thanks Morris,
The springs were all replaced when I had the head reconditioned last year so they should all be good. Cheers, Simon Sooooooo its back to whether: a. the NEW springs are too weak, or b. whether one or more has broked-dead or is not seated correctly etc
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| Author: | norton [ Thu May 14, 2009 9:40 pm ] |
| Post subject: | |
If the points are bouncing it could be seen on one of those cheap dwell meters these meters will also show any wear in the advance plate in the dizzy |
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