Horsepower International Big Bore Motor (2015)

Hello Guys,

As Ken has indicated, I’ve had some time in hospital and am still coming to grips with things, so haven’t followed up on the HPI kit information.

I’ve been trying to finish off a GT40 replica I’m building and was at the point where I started thinking about the next project, my 920 featherbed, but each time I get close, something rears its ugly head. After having both my knees replaced a year ago, which went well, and getting to where I could kick-start my 850 and go for a ride again, earlier this year I was diagnosed with bowel cancer. Bummer. I’ve had chemo / radio treatment, then an operation a month ago, but the outcome hasn’t been as good as predicted, so still a lot of uncertainty there.

At this stage, I’m just trying to recover (more painful than the knees, which were supposed to be bad) and will regroup in the new year. I should be able to move on with things then. Fingers crossed.

Hope you all have a good festive season.

Cheers,

Lance

Sorry to hear that Lance. Hope it all goes well and we see a 920 featherbed build thread soon !

Sounds like 2018 was a tough year for you Lance.
I hope 2019 is much better and your 920 project happens.

Glen

Sorry to hear that, I wish you the Best and hope that your Featherbed project will give you a lot of fun!

Alrighty then. The last few years have been a bit of a shocker for everyone, although here in Western Australia we have not had Covid as other places. It’s actually in here now, but most are vaccinated, so the effects are more controlled.

Anyway, I need, finally, to get this 920 motor rebuilt. It needs a hone as one cylinder is scratched. I’m reading various figures for piston / bore clearances. I’m also dealing with Forgedtrue pistons from HPI. Not sure if that makes a difference. This is not an area in which I have any more than very basic knowledge.

Can someone please advise what I should be telling the workshop to check / work to for piston bore clearances? Does that figure vary with the type of piston? Any other advice?

Any advice gratefully received.

Cheers,

Lance

Good to see you back, Lance. I ran 920 race engines with both Arias (forged) and Fortgedtrue pistons, and found .005" clearance to be the minimum I could use and not have piston seizures. I also found it to be essential to use torque plates during honing, to keep the ring seal at the top of the bore. That was a long time ago, but I think it still holds true. The engine will run just fine with more clearance, but not with less. Hope it works out for you. A decent 920 is a blast to ride.

Ken

Thanks, Ken. Much appreciated.

Glad you made it through Lance.

You guys seem to do a lot of things I would not do. When I raced regularly, it was always in Allpowers C grade against bikes which had capacities up to twice that of my bike. I only had a four speed close ratio gear box. If I geared the bike low, I could lead a race for most of a lap then get passed towards the end of the longest straight. If I geared it high, I could stay in the lead bunch for most of a race. I was too lousy the buy a six speed gearbox. I would never increase engine capacity to get more power when there are better ways. With a smaller capacity motor, you can move the power band up and use more revs. I think that if you ran a 500cc Paton twin in a race full of 920cc Commandos, you would make them look stupid. The weak point in the Commando engine is the balance factor and the crankcases. You cannot increase the revs to get more power. Using heavier pistons is going backwards.

Z900 and H2 Kawasakis are usually only fast in a straight line. You need to get into the straights a long way ahead of them. If they get to the next corner ahead of you, you have to start missing them, as you catch them.