Scooterotica

As above really, why would you do this and in what circumstances and can it only be done with specific knowledge and tools? My reason for asking is that i dropped a ring peg down the side of the barrel (rb) and have had to have the barrel welded and plated (ceramic this time). As the piston was knackered i brought a new DT175 piston and sent this with the barrel when i had it plated. Only issue i have is that the dome on top of the piston looks slightly shallower than the prev DT one. would this mean i need to have it profiled even if i can get the correct squish?

Ta
sef

do you have the old piston to compare ..

RICSPEED wrote:do you have the old piston to compare ..

Not at the mo, im waiting on the barrel. The platers say i should have it thursday. Im hoping to get the scoot ready in time for IOW and have to get a 100 miles on it before then so the plan was to rebuild it over the wend and commute to work on it next week. Issue i have is i dont think im going to get time to get the head profiled if i have to send it off in the timescale i have.

If as you say the dome is lower, could you not do a quick assemble checking clearances and squish and try it out? Not suggesting a long term solution, just to get you to IOW. Performance would be lower, but are you intending to scream there?
When you get back you will have a nicely run in top end and will be able to give it the beans as soon as the head is sorted. Proper back to back testing. ????

it shouldnt be different at all .. but given that you will be running in i wouldnt be to concerned at this point ,until you know for sure i wouldnt worry about it

If it a lower profile dome cant you put a post in the wanteds on a few scooter forums asking if anyone has a head profiled to match a Yamaha it or dt 175 piston it was a popular kit once; could be a few gathering dust in garden sheds;
muppet,

think i will put it back together and see if i can get the squish right and see how it goes. From memory i think you had to put abot 100 miles in on a nicasil barrel, im presuming you can get away with similar with the ceramic.....

sydduckett wrote:abot 100 miles in on a nicasil barrel, im presuming you can get away with similar with the ceramic.....

a mate of mine is a suzuki trained mechanic .. the running in was particularly strict on the rg500's (nicasil) and he saw a s**t load of these come back with dead barrels cos owners diddnt run in correctly .. most would say 500 miles but tbh its not some thing id be happy to advise on really

sydduckett wrote:As above really, why would you do this and in what circumstances and can it only be done with specific knowledge and tools? My reason for asking is that i dropped a ring peg down the side of the barrel (rb) and have had to have the barrel welded and plated (ceramic this time). As the piston was knackered i brought a new DT175 piston and sent this with the barrel when i had it plated. Only issue i have is that the dome on top of the piston looks slightly shallower than the prev DT one. would this mean i need to have it profiled even if i can get the correct squish?

Ta
sef

Hi Sef

I hope you checked the ring peg positions of your DT175 piston as some DT175 models from different years have different spacing & positions for the ring pegs!
The Yamaha model piston used in the RB20 is from the YFS200 & the ring pegs run through the middle of the outer 2 reed boost transfers.
On the TS1 200 cylinder we used the IT200 piston & the ring pegs were set wider apart & ran either side of the single boost port.

I am working on an RB20 cylinder that has worn through the standard Airsal plating in under 2000 miles, mainly around the exhaust port & where the rings stop at the top & bottom of the stroke!
The ring wear marks are worse farthest from the fan cooling it! Customer has used 4% Synthisis 2 all the time so not what I had expected after just a short time, engine shows 24-26bhp @ rear wheel.
Hoping that the cylinder get back from plating soon. He wants it for the IOW to!

As to bedding in a freshly built unit I run it for an hour so that it gets up to temp' at a fast tickover - 2000rpm, as the seals & bearings settle in the idle speed will rise. Having run for that time re set the idle mixture & speed. Then it is checked on the rolling road for any jetting weak spots. The main thing is for the customer not to ride it hard from cold as the piston to bore clearance standard is quite small 0.05mm (0.002") & the ring gap 0.3 to 0.4mm (0.012" to 0.016") if it's below this figure then file the ends of the ring until you have the minimum gap shown. Having what is termed "A cold siezure" is not funny & can result in damage to the bore plating!
If the carb jetting is good & the fuel / oil mix set at 4%, use 95 octane fuel. After about 300 to 500 miles you should have the cylinder unit bedded in. Just remember not to labour the engine in too high a gear, let it rev as then it has more cooling air & fuel/oil mix to lubricate it!

Next Question ~ have you worked out as to why the ring peg came loose?
One of the reasons the old piston dropped a ring peg maybe it due to the motor running too hot! Check the old piston it will have dark oil staining under the piston crown almost looking burnt, also when the piston starts to overheat the bore clearance is reduced & the piston tends to scuff up badly & sometimes shows polished high spots in the area of the 4 piston pin bosses. (Tight piston to bore clearance because of the piston expanding more than it was designed to do) Another cause is poor fuel supply from the tank, check that it can flow 0.5lt in a min, the fast flow taps sold today are not always fast enough! Modified them if need be so on main or reserve they flow well.
Next check how close your flywheel fan is to the cowling - no more than 2 mm gap if you want efficient cooling!

You should be running a BR8ES plug gapped to 0.5mm down from that set at the factory, as the gap is too large for the CDi coil to cope & when the plug carbons up from town running it gets hard to start & misfires under load!

Take care building it & you'll get to the Isle of Wight.

Terrible Taff wrote:

sydduckett wrote:As above really, why would you do this and in what circumstances and can it only be done with specific knowledge and tools? My reason for asking is that i dropped a ring peg down the side of the barrel (rb) and have had to have the barrel welded and plated (ceramic this time). As the piston was knackered i brought a new DT175 piston and sent this with the barrel when i had it plated. Only issue i have is that the dome on top of the piston looks slightly shallower than the prev DT one. would this mean i need to have it profiled even if i can get the correct squish?

Ta
sef

Hi Sef

I hope you checked the ring peg positions of your DT175 piston as some DT175 models from different years have different spacing & positions for the ring pegs!
The Yamaha model piston used in the RB20 is from the YFS200 & the ring pegs run through the middle of the outer 2 reed boost transfers.
On the TS1 200 cylinder we used the IT200 piston & the ring pegs were set wider apart & ran either side of the single boost port.

I am working on an RB20 cylinder that has worn through the standard Airsal plating in under 2000 miles, mainly around the exhaust port & where the rings stop at the top & bottom of the stroke!
The ring wear marks are worse farthest from the fan cooling it! Customer has used 4% Synthisis 2 all the time so not what I had expected after just a short time, engine shows 24-26bhp @ rear wheel.
Hoping that the cylinder get back from plating soon. He wants it for the IOW to!

As to bedding in a freshly built unit I run it for an hour so that it gets up to temp' at a fast tickover - 2000rpm, as the seals & bearings settle in the idle speed will rise. Having run for that time re set the idle mixture & speed. Then it is checked on the rolling road for any jetting weak spots. The main thing is for the customer not to ride it hard from cold as the piston to bore clearance standard is quite small 0.05mm (0.002") & the ring gap 0.3 to 0.4mm (0.012" to 0.016") if it's below this figure then file the ends of the ring until you have the minimum gap shown. Having what is termed "A cold siezure" is not funny & can result in damage to the bore plating!
If the carb jetting is good & the fuel / oil mix set at 4%, use 95 octane fuel. After about 300 to 500 miles you should have the cylinder unit bedded in. Just remember not to labour the engine in too high a gear, let it rev as then it has more cooling air & fuel/oil mix to lubricate it!

Next Question ~ have you worked out as to why the ring peg came loose?
One of the reasons the old piston dropped a ring peg maybe it due to the motor running too hot! Check the old piston it will have dark oil staining under the piston crown almost looking burnt, also when the piston starts to overheat the bore clearance is reduced & the piston tends to scuff up badly & sometimes shows polished high spots in the area of the 4 piston pin bosses. (Tight piston to bore clearance because of the piston expanding more than it was designed to do) Another cause is poor fuel supply from the tank, check that it can flow 0.5lt in a min, the fast flow taps sold today are not always fast enough! Modified them if need be so on main or reserve they flow well.
Next check how close your flywheel fan is to the cowling - no more than 2 mm gap if you want efficient cooling!

You should be running a BR8ES plug gapped to 0.5mm down from that set at the factory, as the gap is too large for the CDi coil to cope & when the plug carbons up from town running it gets hard to start & misfires under load!

Take care building it & you'll get to the Isle of Wight.

Cheers Ian, appreciate the detail you have given. Put the jockey rear brake and new clutch plates in tonight and the barrel is due back tomorrow so will check the piston when i get it back. Do you know what the year is for the piston i need as this seems to be the how they are sold. If I have the wrong one ill put the origonal AF one in for the iow and get the right one when i get back.

Ta again.