heffergm Posted August 19, 2014 Report Share Posted August 19, 2014 Beta (by way of the service manual) tells me I need a new piston at 80 hours. Should I listen to them? Quote Link to comment Share on other sites More sharing options...
dadof2 Posted August 19, 2014 Report Share Posted August 19, 2014 Beta pistons are cast (not forged like Mahle) so there is a theoretical chance of fatigue cracking after a certain number of hours. I would think the chances of your piston cracking at typical low revs trials use is about the same as your chance of winning the lottery. If you were to remove the piston and barrel, measure wear and crack test every 300 hours I would think that more than adequate. Aerosol dye penetrant kits for crack testing cost about £10 to £15 in the UK. Beta aluminium footrests do crack and can snap, this could cause a crash and injury so it is worth crack testing them every few months once they are over a year old. Quote Link to comment Share on other sites More sharing options...
mags Posted August 19, 2014 Report Share Posted August 19, 2014 You can always do a compression check for reference. Then check every 6 months to a year depending on use. A leak down test is great indicator but requires a leak down tester and a compressor. They can be expensive. Once you have reference you can at least check it going off (wearing) with a compression check. Mags Quote Link to comment Share on other sites More sharing options...
lineaway Posted August 19, 2014 Report Share Posted August 19, 2014 Most trials bikes go years if not decades on the same piston. At the rate you are going it will never see 80. Quote Link to comment Share on other sites More sharing options...
heffergm Posted August 19, 2014 Author Report Share Posted August 19, 2014 I've got 65 hours on it. Just curious. Quote Link to comment Share on other sites More sharing options...
dan williams Posted August 20, 2014 Report Share Posted August 20, 2014 OK now you're just looking for problems. Just ride the damn thing. Four or five years from now put in a set of rings and ride it again for four years. Quote Link to comment Share on other sites More sharing options...
billyt Posted August 20, 2014 Report Share Posted August 20, 2014 (edited) **** Dan. Why so cautious. I would only change one of the rings after four years and change the other ring after eight years. I agree, just ride the damb bike and stop looking for an issue that no one has had or asked about. I have been on this site since it was called Trials Action and now Trials Central and can bet that you are the first person to ask about changing a piston in such a short time period. Edited August 20, 2014 by billyt Quote Link to comment Share on other sites More sharing options...
copemech Posted August 20, 2014 Report Share Posted August 20, 2014 (edited) I thing the 80 would be a good estimate for normal road running at sustained high rpm. Pity you will likely never achieve that on a trials bike! Same reason they tell you to use twice the oil you need in the mix! Edited August 20, 2014 by copemech Quote Link to comment Share on other sites More sharing options...
dan williams Posted August 20, 2014 Report Share Posted August 20, 2014 (edited) Actually Billy I was thinking you run them for two years then flip them over so you wear the other side and save money. ? Edited August 20, 2014 by dan williams Quote Link to comment Share on other sites More sharing options...
dan williams Posted August 20, 2014 Report Share Posted August 20, 2014 (edited) Hey heffergm, I'm just joking. I know you're new here so I should explain, Billy is one of the uber gurus like Jon Stoddley (sp?) over on the GasGas forum. When I want to be humbled I dip into their knowledge. Edited August 20, 2014 by dan williams Quote Link to comment Share on other sites More sharing options...
goudrons Posted August 21, 2014 Report Share Posted August 21, 2014 As with all parts that move against another, they wear. Beta and most other manufacturers state a guide to check and compensate for this wear. The guide takes into account the piston it's self, the piston rings and the cylinder bore. This bore isn't a steel liner like days of old, modern cylinders are made of alloy for lightness and a special, thin, chrome like plating is adhered to it. This plating is fairly expensive compared to reboring a steel liner and cannot be rebored as a steel liner would be. Another method which works out a little cheaper is needed to compensate for wear and keep the engine sweet as. You'll find the guide will indicate the use of new pistons. Betas (and others) way around this wear and expense is to offer pistons in increasing sizes, not massive jumps in size like older bikes would use on a rebore (.25, .50, .75 etc) but pistons microns larger than the last, usually idenified by letters A, B, C, D. So a new engine will start out with an A piston, run for X hours/miles, measured and if needed a B piston fitted to keep the fine piston to bore clearance used on these modern engines, and so on until D is reached (and worn out), then a replate is needed, you'd then supply the replater with an A piston to start again. Believe it or not, this is far cheaper than fitting a new piston and replating the cylinder everything, the replate would only be needed once the bore had become too worn for D piston. There is a uk company that replate, Langcourts of Weston Super Mare, Quality is good, probably better than factory. Quote Link to comment Share on other sites More sharing options...
heffergm Posted August 21, 2014 Author Report Share Posted August 21, 2014 **** Dan. Why so cautious. I would only change one of the rings after four years and change the other ring after eight years. I agree, just ride the damb bike and stop looking for an issue that no one has had or asked about. I have been on this site since it was called Trials Action and now Trials Central and can bet that you are the first person to ask about changing a piston in such a short time period. You're joking right? (please say yes). I asked out of simple curiosity, not any feeling of impending doom. The manual says 80 hours, I've put 65 on mine in the last 4 months and am going to blow way past 80 by the end of the season. Heaven forbid I ask how many hours people are typically getting on pistons. Quote Link to comment Share on other sites More sharing options...
dadof2 Posted August 21, 2014 Report Share Posted August 21, 2014 Just want to correct what I said on my previous post, I meant to say it is the aluminium footrest brackets that crack, not the footrests. Quote Link to comment Share on other sites More sharing options...
mags Posted August 21, 2014 Report Share Posted August 21, 2014 (edited) Heffergm, Like above... don't assume all motors need a new piston at 80 hrs far from it. It may of course but the idea would be to find out for sure and definately save you money if not needed. Do a standard compression test, its a good, basic indicator of the need to delve further into the topend with dial bore gauges and piston micrometers. A cylinder leakdown test would be even better and a local shop may be able to do this for a reasonable price? If new rings/piston needed you will at least have a cylinder compression reading for when it needs rebuilding again. Once done and run-in do a compression test again for a "new" benchmark. Check with the local bike shop mechanic if its easy to compression check with kickstart only bike? I've only done electric start bikes with comp test and leak down with kickstarts. Mags Edited August 21, 2014 by mags Quote Link to comment Share on other sites More sharing options...
dan williams Posted August 22, 2014 Report Share Posted August 22, 2014 There is a lot of joking here. Basically you shouldn't need a piston for many years. What we're saying is don't worry about it. Quote Link to comment Share on other sites More sharing options...
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