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hulmie

Any Ideas What's Going On

28 posts in this topic

Thanks Larry, I'll take some extra tools with me next trial, I've just ordered a couple of larger jets so they should get me into a better adjustment range will try those first then have a look at the timing if the jets don't help while I'm there, it only takes 5mins to get at the timing plate

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Just thought I'd update this post I've finally sorted the running problems. First fault (starting/reving)was the brand new carb which has been swapped for a new amal premier carb, the second fault was a combination of things (gettin hot/pinking), turns out these Villiers engines have a usefull feature of a drain plug in the crank cases, which had come loose on mine and was letting in a small amount of air making it run hot, so that got a new copper washer and some thread tape making it run a lot better but not perfect, whilst talking with a couple of riders whilst out practicing they mentioned about the squish with it having a rebuild, so that was checked and found to be very tight/narrow so I've used a copper head gasket I had off another bike and what a transformation the bike is a complete different animal, so thanks to those who posted ideas and maybe this might help others in the future because there's nothing worse than a thread with no update on whether a fault has been fixed, here's a pic of it now it's finished 20170310_111823.jpg

Edited by hulmie
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I'm surprised that a small squish clearance was causing the problem as I've always worked on the assumption that squish clearance should be small. what did you start with? And what have you got now? The bike's looking very handsome, by the way.

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There 

22 minutes ago, trapezeartist said:

I'm surprised that a small squish clearance was causing the problem as I've always worked on the assumption that squish clearance should be small. what did you start with? And what have you got now? The bike's looking very handsome, by the way.

It was quite a lengthy process trying lots of things one at a time, it got to a point where nothing i did changed how it ran for the better, it would knock/pink under load but once you were on the flat it would rip your arms off once it got going, I didn't measure the squish but took off the head and tightened back down the barrel (head bolts hold the barrel aswell) and the piston was sitting above the top of the cylinder so I took a punt on using an old head gasket that my uncle had which was the correct bore and was I think .9mm thick and it has totally transformed how it runs. Thanks that pic was taken last week on a trail by Hawks Nest 

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So the clearance is 0.9+(whatever it was before). That's at least double what I was using on my kart engines. And I used to adjust the squish with paper gaskets on the cylinder base.

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I've never messed around with the squish on any of my enduro bikes, i used to get a local kart engine builder to do any major work for me as they would fly once he had finished with them so I wouldn't know what would be the best clearance  

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2 hours ago, hulmie said:

I've never messed around with the squish on any of my enduro bikes, i used to get a local kart engine builder to do any major work for me as they would fly once he had finished with them so I wouldn't know what would be the best clearance  

More likely to be the compression ratio if you are using a gasket of nearly 1mm..... the squish band controls pushing the charge into the centre of the chamber in the head for a good burn.

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Every day is a school day B) like I said I've done basic rebuilds before and never had to mess with any engine like I've had to with this one, it was a non runner when I got it and it's been a pain in the backside 

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As long as your bike runs ok to your liking; that is what matters.

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Yeah im just glad that ive got it to stop sounding like a bag of spanners and possibly ruining a rebuild, it runs great and has more than enough power for me

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On Sunday, March 26, 2017 at 0:40 PM, oni nou said:

More likely to be the compression ratio if you are using a gasket of nearly 1mm..... the squish band controls pushing the charge into the centre of the chamber in the head for a good burn.

Bike looks fantastic a great resrstoration job. 

I too think compression ratio was causing the problem, Greeves produced similar looking cylinder heads with very different combustion chamber shapes for all types of motorcycle sport.

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"Pinking", "knocking", "bag of spanners". I'm just wondering if you actually had zero squish clearance to start off with ie the piston was hitting the head. In which case an extra 0.9mm of clearance may be a little excessive, but not much.

Edited by trapezeartist

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On 29/03/2017 at 11:21 PM, trapezeartist said:

"Pinking", "knocking", "bag of spanners". I'm just wondering if you actually had zero squish clearance to start off with ie the piston was hitting the head. In which case an extra 0.9mm of clearance may be a little excessive, but not much.

There was no signs of any piston to head contact, but it must have been close as when the barrel was torqued down the piston was above the top of the barrel, it was the only thing I didn't check when I originally built the engine 😶, it would knock mainly under heavy load pulling up steep hills, on the flat it would be fine, the timing had been checked multiple times and I'd tried different settings all made some difference (good and bad) but non cured the fault this is the only change that has stopped the knocking, so weather it be squish or compression im not sure but it runs great now, it would be nice to get an expert go through it and find out exactly how it should be set up or how close ive got it, as TRF says there are many different combinations of these engines so it may have been a bit of a lash up in the past lol

Edited by hulmie

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