animal47 Posted December 7, 2016 Share Posted December 7, 2016 I decided to build a cheap engine as had a spare 4 bolt bottom end lying around so took a punt on a cheapy ported 29 from Rcmodelz. Now for some reason I can't get it to seal properly where the isolator block bolts on, I have tried both the km and zenoah gaskets but with the same results, I am using a zenoah isolator so is it worth trying a km one, are they known for bad casting here. Quote Link to comment Share on other sites More sharing options...
Carpmart Posted December 7, 2016 Share Posted December 7, 2016 majUnfortunately my friend, your suffering from the atrocious build quality of KM heads.. they seem excellent value, but are in fact just junk! TBH, Zenoah and CY are not well made either, but KM demonstrates cheapness of the highest order. My guess is that all the heads are made in the same place. Then Zenoah get first choice CY second and the rest get what's left... KM thenbuy up all the crap no one else wants.... Quote Link to comment Share on other sites More sharing options...
animal47 Posted December 7, 2016 Author Share Posted December 7, 2016 Aha so not unusual then, that is not acceptable regardless of whether it is cheap, it should at least be fit for purpose. Quote Link to comment Share on other sites More sharing options...
Fly In My Soup Posted December 8, 2016 Share Posted December 8, 2016 (edited) On 07/12/2016 at 05:31, animal47 said: I decided to build a cheap engine as had a spare 4 bolt bottom end lying around so took a punt on a cheapy ported 29 from Rcmodelz. Now for some reason I can't get it to seal properly where the isolator block bolts on, I have tried both the km and zenoah gaskets but with the same results, I am using a zenoah isolator so is it worth trying a km one, are they known for bad casting here. You obviously replaced all gaskets with new yes? Try eBay for a used alloy one Edited December 8, 2016 by Fly In My Soup Quote Link to comment Share on other sites More sharing options...
animal47 Posted December 9, 2016 Author Share Posted December 9, 2016 Yes all gaskets have been replaced twice. Quote Link to comment Share on other sites More sharing options...
Mitrab36 Posted December 9, 2016 Share Posted December 9, 2016 Your talking about the isolator for the carb yeah? So essentially the inlet manifold. First thing to do is work out exactly where the fault is instead of throwing new gaskets at it and overtightening bolts. Easy to do with a steel ruler and a torch or even just the isolator block. Hold it up tight and where the light leaks you have a gap !!! simples. This will tell you which one of the faces has a high or low spot. Then with some wet & dry on a little block of MDF you can lap the faces to meet perfectly. Then fit the isolator on it's own on the head lightly and check with the torch again. It was quite a common thing to do with 2T race MX engines where a perfect seal is essential. Remember the parts your fitting together came from 2 different factories, so although it would be nice if they fitted first time, in reality tolerances have to be allowed for. Sounds like a lot of work but unless the new head is properly warped should only take about 30mins to do. If there's a massive gap then you just got unlucky with a bad head and they should exchange it. Quote Link to comment Share on other sites More sharing options...
RCbutcher Posted December 9, 2016 Share Posted December 9, 2016 It's possible the head has a deformity or other out of nowhere issue any brand can suffer. Hopefully it is just a tinker time fix. Zenhoas have been doa too. I'll be breaking in my 29cc ported soon hopefully it goes well lol. Been stood 2yrs now new in the cubby. But it's finally time very soon. Quote Link to comment Share on other sites More sharing options...
Carpmart Posted December 9, 2016 Share Posted December 9, 2016 4 hours ago, Mitrab36 said: Your talking about the isolator for the carb yeah? So essentially the inlet manifold. First thing to do is work out exactly where the fault is instead of throwing new gaskets at it and overtightening bolts. Easy to do with a steel ruler and a torch or even just the isolator block. Hold it up tight and where the light leaks you have a gap !!! simples. This will tell you which one of the faces has a high or low spot. Then with some wet & dry on a little block of MDF you can lap the faces to meet perfectly. Then fit the isolator on it's own on the head lightly and check with the torch again. It was quite a common thing to do with 2T race MX engines where a perfect seal is essential. Remember the parts your fitting together came from 2 different factories, so although it would be nice if they fitted first time, in reality tolerances have to be allowed for. Sounds like a lot of work but unless the new head is properly warped should only take about 30mins to do. If there's a massive gap then you just got unlucky with a bad head and they should exchange it. 2 hours ago, RCbutcher said: It's possible the head has a deformity or other out of nowhere issue any brand can suffer. Hopefully it is just a tinker time fix. Zenhoas have been doa too. I'll be breaking in my 29cc ported soon hopefully it goes well lol. Been stood 2yrs now new in the cubby. But it's finally time very soon. All that you say is correct. What you're not acknowledging is that if the gasket surfaces on a new engine component are not completely flat, then it's not fit for purpose and shouldn't be sold. It's not an isolated incedent either. I bought one KM head and it's junk...the OP has a junk head, that 100% failure in my experience! Quote Link to comment Share on other sites More sharing options...
evssv Posted December 9, 2016 Share Posted December 9, 2016 I almost bought a cheapo 29 head kit. ...but i ended up with a genuine cy kit from rob at irc and its sweet...as i was told all other head kits r junk...now it's run in. ..me db.....It runs like a champ. .Well happy! ! Quote Link to comment Share on other sites More sharing options...
Mitrab36 Posted December 9, 2016 Share Posted December 9, 2016 Oh dear I feel another KM / clone parts bashing thread starting...... Quote Link to comment Share on other sites More sharing options...
Fly In My Soup Posted December 9, 2016 Share Posted December 9, 2016 On 07/12/2016 at 05:31, animal47 said: I decided to build a cheap engine as had a spare 4 bolt bottom end lying around so took a punt on a cheapy ported 29 from Rcmodelz. Now for some reason I can't get it to seal properly where the isolator block bolts on, I have tried both the km and zenoah gaskets but with the same results, I am using a zenoah isolator so is it worth trying a km one, are they known for bad casting here. Can't comment on km quality, I'm sure many could and will, but in regards to sorting this issue of the I. block not sealing, there's only 3 objects in the equation, head face, gasket, isolator block, you've eliminated the gaskets, im assuming youve eyeballed and handled the head at the point where the isolator block and gasket meet it to know if theres any clearly visibly major scores/scrapes or irregularities, so common sense would dictate you source another, preferably new isolator block to eliminate this also. Also, if your going down the route of modifying/sanding the isolator block I would advise not to sand the face of the isolator block where the gasket sits, as they generally have a raised 0.2mm outline of a gasket on the block itself to promote a good seal, removing this by sanding would in effect lessen the chance of a good seal Raised lip of isolator gasket silhouette; If I was attempting to find a solution I would source an alloy i. block, and instead of using just one gasket to seal the block to the carb I would employ three, two normal and a Teflon 0.5mm 'hard' gasket sandwiched in between. So would go from engine outwards ; - rubber isolator gasket- Teflon isolator gasket-rubber isolator gasket- alloy isolator block- carb gasket- carb - air filter gasket- air filter So everything as you normally would, bar the three gasket sandwich at the head side. Hope that helps in any way! P.s did the motor come with a warranty? Quote Link to comment Share on other sites More sharing options...
animal47 Posted December 10, 2016 Author Share Posted December 10, 2016 I really appreciate all of the advice and my next step is to do some investigation into it although I am pretty sure that it will be the face on the head as the isolator block was absolutely fine on the previous head, I suppose in theory it could have taken on the shape of that head and slight differences in this new one are too much for the gasket to make up. A new isolator along with a teflon spacer and gaskets sounds a good idea although I am in 2 minds about whether to stop being a tight wad and buy a decent top end as this thing is no doubt going to be way underpowered in comparison to the Stevo top end that was previously fitted and let's be honest I can't realistically expect to build a competitive race motor for £35. That said though anything that I am paying good money for should still be fit for purpose. Quote Link to comment Share on other sites More sharing options...
animal47 Posted December 10, 2016 Author Share Posted December 10, 2016 Just been out and pulled it all apart and whilst I can't really tell if the head is straight, the isolator is very warped which I guess is probably my own fault for over tightening. Are the isolators only supposed to be just nipped up then. Quote Link to comment Share on other sites More sharing options...
andyknight Posted December 10, 2016 Share Posted December 10, 2016 just to add some balance here, I've had several KM head kits and not had any problems with isolator block sealing etc. I'm not saying there aren't issues with some heads but the 2 I have had have been fine. I built up a spare engine a couple of months ago and had no issues with it. Quote Link to comment Share on other sites More sharing options...
Fly In My Soup Posted December 11, 2016 Share Posted December 11, 2016 On 10/12/2016 at 12:59, animal47 said: Just been out and pulled it all apart and whilst I can't really tell if the head is straight, the isolator is very warped which I guess is probably my own fault for over tightening. Are the isolators only supposed to be just nipped up then. They need to be tight, to get a good seal, but not over tight so your bolts are about to munch their way through the i block itself. Post a pic of the warped block if Poss Quote Link to comment Share on other sites More sharing options...
Fly In My Soup Posted December 11, 2016 Share Posted December 11, 2016 I still say try a new I.block first Quote Link to comment Share on other sites More sharing options...
Fly In My Soup Posted December 11, 2016 Share Posted December 11, 2016 22 hours ago, andyknight said: just to add some balance here, I've had several KM head kits and not had any problems with isolator block sealing etc. I'm not saying there aren't issues with some heads but the 2 I have had have been fine. I built up a spare engine a couple of months ago and had no issues with it. It does seem doubtful that the head face is so irregular that the I blockwon't seal, as if it was that out,you would generally be able to see it with your naked eyes. New I block on eBay for less than a tenner posted Quote Link to comment Share on other sites More sharing options...
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