TF100 issues

[bucketracer]

I was wandering if the clutch springs are to soft ? or do i need to look into different plates??

The Team ESE clutch plates sometimes become hard and glazed and slip after a bit of a caning.

After a bit of a scuff up on CRC whetted 180 grit wet and dry and a glass plate to remove the glazed surface the clutch's work OK again.

[SS90]

Hi all.

well the clutch suggestions nearly worked, only slipped a little bit. so one down, Thank you all for the input.

So here another one.

After a goodish weekend in Wellington, I started to pull down my engine to replace the broken casing (engine mount broke with some casing as well) which requires a near complete strip down.

anyway, attached are a couple of photos of the piston with funny burn marks (matching the exhaust port shape) and the exhaust side. (plus the first ~inch of the exhaust was a "not so nice" grey colour as well).

now it was suggested that maybe I had my exhaust lengths incorrect? and maybe this is so given the piston marks and grey header.

Any thoughts on the cause of the marks? or if it is a major issue or not?

This piston has only done about 2 hours (Taupo GP, Manfield and Wellington); not a pretty sight

I have never actually seen that sort of marking on a piston before Bert, But I notice that there are "streaks" coming up from the ring land to the crown of the piston, and this normally indicates that your chamfering of your exhaust port is incorrect, (and/or) your exhaust port is very very wide (perhaps "on the limit")...is it possible your could post a port map?

If that theory is correct (and the shape/size/design) of your exhaust port is causing premature ring wear (as has been suggested) you can check the ring wear theory very easily, simply by putting the ring into the cylinder, about half way down, and measure the ring gap with a feeler gauge.

A good rule of thumb for an air cooled engine is 3 thou per inch of bore.

If you find that your gap is much more than this, this could well be the problem.

How many hours have you run on that piston/ring combo?

For example, if the ring is shown to be worn, and you have only run 5 or 6 hours, then I would suspect something else causing the ring wear (exhaust port size/shape is the biggest culprit here, and is easy to prove or disprove if this is the culprit), whereas, if you have run in excess of 20 hours on a KT100 piston and ring, then a knackered ring is acceptable.

On a Kt100, I am pretty sure you run a ring for about 7 hours before replacement, but they do rev to something like 15,000, and if your TS is doing that, you need a medal!

I think 10 or 12 hours on a ring would be acceptable in your application.

Perhaps if Speedpro could let us know how many hours he gets from a piston/ring combo, you could use that has a yard stick.

[gav]

This piston has only done about 2 hours (Taupo GP, Manfield and Wellington); not a pretty sight
You not read this bit SS ?

[Bert]

I have never actually seen that sort of marking on a piston before Bert, But I notice that there are "streaks" coming up from the ring land to the crown of the piston, and this normally indicates that your chamfering of your exhaust port is incorrect, (and/or) your exhaust port is very very wide (perhaps "on the limit")...is it possible your could post a port map?

If that theory is correct (and the shape/size/design) of your exhaust port is causing premature ring wear (as has been suggested) you can check the ring wear theory very easily, simply by putting the ring into the cylinder, about half way down, and measure the ring gap with a feeler gauge.

A good rule of thumb for an air cooled engine is 3 thou per inch of bore.

If you find that your gap is much more than this, this could well be the problem.

How many hours have you run on that piston/ring combo?

For example, if the ring is shown to be worn, and you have only run 5 or 6 hours, then I would suspect something else causing the ring wear (exhaust port size/shape is the biggest culprit here, and is easy to prove or disprove if this is the culprit), whereas, if you have run in excess of 20 hours on a KT100 piston and ring, then a knackered ring is acceptable.

On a Kt100, I am pretty sure you run a ring for about 7 hours before replacement, but they do rev to something like 15,000, and if your TS is doing that, you need a medal!

I think 10 or 12 hours on a ring would be acceptable in your application.

Perhaps if Speedpro could let us know how many hours he gets from a piston/ring combo, you could use that has a yard stick.

The ring wear is interesting (I was intending on putting a new one in anyway). The exhaust port is very wide, attached is a port scan. Also of note (which i forgot to provide) last year she seized, (on the exhaust face as normal), but there was considerable piston damage in the same places.

as for run time: must only be around the 2 hour mark. give or take a bit.
about a 20min run in, and a few laps at the pre-mentioned meetings. (hardly finished at any of those)

and o'yea she revs mate, not to 15k but well higher than what mister Suzuki made it too do.

[SS90]

This piston has only done about 2 hours (Taupo GP, Manfield and Wellington); not a pretty sight
You not read this bit SS ?

Clearly not.

I would (with-out seeing it) suspect that after 2 hours use and seeing the sort of blow by and scuffing that the picture has, that there is something not correct with either the ring gap from new, or, like has been suggested, premature ring wear due to either excessive port width (or even inlet port as well), or perhaps unchamfered ports.

[SS90]

The ring wear is interesting (I was intending on putting a new one in anyway). The exhaust port is very wide, attached is a port scan. Also of note (which i forgot to provide) last year she seized, (on the exhaust face as normal), but there was considerable piston damage in the same places.

as for run time: must only be around the 2 hour mark. give or take a bit.
about a 20min run in, and a few laps at the pre-mentioned meetings. (hardly finished at any of those)

and o'yea she revs mate, not to 15k but well higher than what mister Suzuki made it too do.

Thanks Bert,

How wide is that exhaust port? (in mm, or perhaps do you know as a percentage of bore diameter measured across the chord?)

[Bert]

Thanks Bert,

How wide is that exhaust port? (in mm, or perhaps do you know as a percentage of bore diameter measured across the chord?)

bore = 52
exhaust port top = 39.5
exhaust port bottom = 34.6

approximately. and all the ports are chamfered and have clean radius/arced tops to re-seat the rings, well at lease attempted anyway.

[SS90]

bore = 52
exhaust port top = 39.5
exhaust port bottom = 34.6

approximately. and all the ports are chamfered and have clean radius/arced tops to re-seat the rings, well at lease attempted anyway.

Hi Bert, I think that you will find that your exhaust port is too wide.

39.5 is over 75% of the bore width, and if you calculate that against the chord, it is even higher......

I think it is a true testiment to the strength of tha Yamaha piston and rings to be still running!

[SS90]

If you need to calculate your chord Bert, follow this link, you can download a trial.

http://www.machinist-calculator.com/Chords.html

You only need 2 values, and it will do the rest...ideally, you are looking for a chord length of LESS that 70%.

[Bert]

Cheers for that. I've just about finished building a excel workbook with all porting calculations (I will share once finished).

Yes well, I had a quick look at a couple of other barrels sitting in the shed. all ported by the same man (not me) and they are all rather large and similar shape in the exhaust port...

Basically similar to Bells earlier two stroke tuning book covering the RM125m (i think) the porting matches other than the bridge.

o'well, I'll slap another piston/ring in it and she if she will survive another few meetings.

I still am interested in the burn pattern & grey exhaust header, in relation to the potential exhaust length issues???.

[SS90]

I still am interested in the burn pattern & grey exhaust header, in relation to the potential exhaust length issues???.

I think the burn pattern is caused by the ring poking too far into the exhaust port and exhaust gasses leaking past the ring when the port opens.

Remember something like 80% of the exhaust gasses burst out the exhaust port the moment it cracks open, if that ring can't do it's job at this high stress moment....... That's my play on things anyway!

Like I say, I have never seen a piston look like that!

[F5 Dave]

I think SS is on the money here, but again I haven't seen one with quite such a pattern. Exhaust design a red herring I'm sure. (lets start talking when you have weird in-transfer patterns).

[Bert]

I knew you would be around somewhere Dave.

Sitting back a reading this again, I happy with SS conclusions. bugger it all. the problem is now what to do about it for a short term solution... (one meeting)

Me thinks a resurrection of another barrel and new piston to get me through the start of the session. with the hope that I can mod the exhaust to suit. all in a week...

and a standard crank and rod....

I'm glad I'm on my 2 week christmas holiday.

[F5 Dave]

Well measure the std barrel & see if it is worn & if the ring is worn. If just the ring then replace that, after all you are just trying to keep it going until the new engine is in place. If the bore is worn then you will need to attend to that. 2thou clearance in an aircooled engine with a steel bore should be safe. Run lots of oil, 40:1 of decent oil should be ok but keep adding more as the revs go beyond 10/11,000.

However; Look at the chamfering. you want to present a surface to the ring which is symmetrical & gentle. If the port roof is flat, or worse square edged, that doesn't mean the chamfer needs to look like that to the ring (even if the gas flow via the piston shape sees it differently). Super big eyebrow to the corner & one either side will make the ring look like it has a round port to ease it back in & out of support without 'seeing' the corners.

[Bert]

Cheers Dave & SS for your help.
I'll measure it all up and work on the best course of action.
At first glance today the bore looks quite good (still has the cross hatch visible all the way around) and the piston, outside of the burn marks still has most of its detail; so lets hope its just in need of a ring!!

I'll give the ports a check over as well.
The exhaust port roof is slightly higher in the middle / rounded shape; the corners are quite radius, not fully sure what you mean by eyebrow sorry.
I assume that you mean this?

Shed time.

some progress. went down and talked to my man at the shop. the bore isn't round anymore. new larger ring and lots of oil. and laugher lots of laugher.,...

quite a lot of measuring, turns out that the barrel above the exhaust port is slightly dished, suggesting that this is going to be an issue of a good seal.. but he suggest (like all go salesman) that if i keep chucking rings into it then it should last.
The underside of the piston was a nice brown colour (and in o.k condition), but has been very hot at some stage (little goldy flecks); at manfeild I dropped my magneto coils (advancing the timing) so this might explain things....

Better photos cn be found: http://www.kiwibiker.co.nz/forums/al...p?albumid=2701

as for the burn marks on the piston; he did suggest that the exhaust length maybe to short (and it did show signs of burning in the transfers). and I didn't prompt this conversation either.

anyway, its going back together as is (with new ring) and we'll see how long it will last for.

On the side note, we had a coffee and a chat/photographs about the racing over Easter, along with some discussion regarding the track up here and the issues of old.
Maybe just maybe if a presentation was done to the Palmerston North Kart club regarding the new requirements adopted in Wellington (nylon crash protection etc). and some feedback from the Wellington kart club on behaviour/track damage etc; we might have a outside chance. but it would require considerable groundwork and would have to run under MNZ.

Back to the shed.