Advice on minor nip up.

[shocky]

I find myself agreeing with Shocky more and more as I read this forum :shocking:

My SX150 had a tight rebore and heat seized continually. I bought a 175 kit to run while I sorted it yep, guess what, that heat seized too (I found out too late that the bore clearance on these kits is a bit random to say the least!).

So I got a Sealey 3 leg hone for about £20, from Machine Mart I think, and gave the SX a good going over. Telescoping gauges are a poor substitute for a bore mic, but worked for me. I gave it 5 or 6 thou clearance as I was totally pi$$ed off with it seizing and it's not given a bit of concern since.

I'm going to hone the 175 kit next, with a bit of porting (couresty of sizes from Adam Winstone ).

Good luck, and let us know how you get on!

!

[storkfoot]

..........., but I suppose if its done wrong you could do damage....

Yeah, I think that's the issue, this sort of information is useful to people who know exactly what they're doing______I just don't want your average rally going scooterist to think that subjecting all pistons to files, wet n dry, and grinding paste, will solve heat seizure problems

[byron]

Dave Webster told me to lap in my Yam piston prior to running it on the road, back in 1981....done it too a few since, no need for long the running in process, but I suppose if its done wrong you could do damage....

so by how much could this decrease the running in period on an iron barrel ??
[if all goes to plan] going to have one to do later in the year, there's only so many times riding sedately around the norwich ring road is something to look forward to

[J1MS]

Dave Webster told me to lap in my Yam piston prior to running it on the road, back in 1981....done it too a few since, no need for long the running in process, but I suppose if its done wrong you could do damage....

so by how much could this decrease the running in period on an iron barrel ??
[if all goes to plan] going to have one to do later in the year, there's only so many times riding sedately around the norwich ring road is something to look forward to

A couple of examples of how I went about this process and how it effected the running in...

Lapped my Yam piston in with a very fine lapping paste done in two stages, Then ran the scooter gently at first just to bed the rings in, about 200 miles later I was running at Motorway speeds....

Lapped in an a heat seized barrel and piston (for a mate Kev now living in France) on a near standard SX200 which always seized if it went much over 40mph even after he had run it in ...after lapping it in he took it easy for about 50miles then road it at normal speeds..... never seized after that.....

A group 3 barrel I ported back in 84-85...KH 400 piston & shortened barrel, bored to 3 thou clearance...then I lapped in the new piston prior to building the engine ....First time the engine was run was at Donnington...out of a field of 30 in a newcommers race....The rider finished 3rd overall....This was at the Donnington International....The running-in period was the warm up laps...then flat out up to approx 80mph....It can be a very good way of reducing the running-in period....But can shorten the life of a barrel for road use....and the choice of lapping compound can make a big difference...I used to do it in two stages....First with a fine lapping paste diluted with parafin.... then the final lapping in, was done with a medium rubbing compound meant for paint finishing.. again with a little parafin....Im not saying this is the right way.... but its the way I went about it...

[byron]

A couple of examples of how I went about this process and how it effected the running in...

thanks a lot, that's really useful

[156 D]

In this day and age anything that saves time is always considered the best way to go!!......Why is it called "Valve Grinding Paste"?......yes...that`s right because it is for grinding in valves which are made of a very hard and treated material....you should not go anywhere near an alloy moving part with this paste as it will bed itself into the soft alloy and you cannot remove it merely by washing and washing.....use it on the cylinder head with a sheet of glass ..yes, as the cylinder head and cylinder do not move against one another....OK..so some have used it on piston`s to lap them in ,but if you read about those instances they are all related to race tracks so that it is a quick and instant fix so you can be in the next race.....the actual engine would not last very long for the normal road use.... So, you are all at your own peril....if you actually bothered in the first instance to make sure your bore clearances are correct and only use well known manufacturers to purchase from, but then of course sometimes money comes into it,or how much money....that £18 honing tool sounds pretty good if your tolerances happen to be tight, it sounds cheaper than valve grinding paste and an awful lot cheaper than another re-bore and piston .....IMO just run it in properly for road use and bugger the time it takes, you will end up with a lot better engine and also be proud of the fact you sat on that scooter seat for all those hours!..................