heat problem with malossi 136

[jean-yves]

Hello I'm French and sorry I don't speak a word of German language, that's why I do not usually post on this forum, but there I really need to find a solution for my problem, so I'm speaking about it to you...

My engine setup ;

I've a 136 Malossi, rebored to 58,3 on a PK ETS motor.

Transfers are enlarged, and admission in the casing is stopped with epoxy.

I've a full circle mazzucchelli crankshaft modified to fit in the ETS casing

I've increased port timing to 186/130 (and boost-ports are now at the same height than the principal admission port and directly joined to the admission)

piston window is also enlarged

The exhaust is a sip evo curley (the 2003 model) i've reduced the silencer (5cm)

I use a pk lightened flywheel (1,290kg) with hp4 fans and naturally an electronic ignition, adjusted to 17 degrees

2,54 primary ratio with straight cog and Zirri short 4th gear

I've modified the Malossi reed valve direct intake (amplified petals aperture, reduced the length of the pipe, and enlarged the diameter to 30mm), now I'm using a Mikuni TM28 with ramair air filter but want to put a 30 or 32tmx later... (money, money...)

Squish clearance was reduced to 0,7mm

Using 98 octane fuel with (and that's amazing) 5% of TTS Castrol synthetic oil

My problem ;

Everything is ok when the scoot is on the stand boot, the engine reach high speed fast, do not feel hot... it could stay many hours long like that

But when I'm driving it, slowly because I'm grinding it, when I'm in 3 or 4, in low rmps ( maybe 4/5000 rpm, no more ) the motor seems to take too much lean mixture and heat very quickly

I've tested bigger jet (main and idle), modified needle postion, tested any advance values (from 14 to 22), increased squish clearance to 2,2mm, tested another carb (30phb dell'orto), another petals block (malossi fiberglass), others sparkplugs more cold, but nothing beter happens... my engine allways heat too much (

I know I've not spoke about every important things and details, and it will take a long time to find my problem but I will try to reply you the more efficiently I can and put pics in any cases

At last, this bike is not my daily driver and I just want use it for races...

Thanks by advance,

jean-yves

Bearbeitet 2. Mai 2005 von jean-yves

[jean-yves]

some pics...

Bearbeitet 27. April 2005 von jean-yves

[kan_Kuma]

Hello Jean-Yves

Nice scooter, nice layout :)

The problem you're having with your 136 might be the fault of the exhaust you're using.

You said the problems arise during slow uptake at around 4000-5000 rpm.

Take a look at the dyno runf of a SIP curley here:

Here you can see the quite heavy indenture in the graph at around 5700 rpm. I don't know if you're using a rpm gauge but imho I guess your problem might be linked to this.

Have you tried using other exhaust pipes?(Zirri Silent) Might be a good idea to do so, just to be sure.

Another thing: Looking at your piston, I found your piston window enlargment to be rather "adventurous". What mileage do you have with that layout? Those pistons seem to have a tendency to crack just around the piston window, mainly because of the large window and the quite thin skirt left under that window, which can get caught in the lower side of the intake port. Your skirt at that position seems to be rather thin.

Cheers

Chris

[gertax]

Another thing: Looking at your piston, I found your piston window enlargment to be rather "adventurous". What mileage do you have with that layout? Those pistons seem to have a tendency to crack just around the piston window, mainly because of the large window and the quite thin skirt left under that window, which can get caught in the lower side of the intake port. Your skirt at that position seems to be rather thin.

<{POST_SNAPBACK}>

in other words: your piston is a timebomb, and quite a big one in my eyes.

to jet for cruising rpm it may be necessary to abnormally richen the slow jet, especially with pipes hitting rather hard. But as long as your engine does not seize there is no problem with it getting hot.

[jean-yves]

ok, for the piston I understand/know my mistake, when I've a Dremel in my hands sometimes I can't stop myself :grins:

when I look at it, I also think it will break one coming day... if I keep this cylinder (if I solve my problem), I'll change it soon !

I've not yet installed a rev counter but you are right, I think it's corresponding to the flat curve of the curley at 5/6000... and no, I've not tried another exhaust...

but my problem is that when I'm in this range, my engine heats really quickly a lot, the sparkplug become white and very dry, and the consequence appends rapidly (no more than 1 minute), the engine seize ! (

the original idle jet is a 15, I've changed it for a 30 one, but I think I can still increase it because the 'enrichment screw' is only half turned...

I use a 250 main jet and the needle is at the last position (really too rich but to prevent hot temp... with unfortunately no effect )

Bearbeitet 2. Mai 2005 von jean-yves

[jean-yves]

I've a race at the end of this month and have no idea from where come my problem... do somebody have an idea ?

What else could I try ?

I'm sicken, really :plemplem:

Bearbeitet 2. Mai 2005 von jean-yves

[KTy]

I thought you had a TM27 Mikuni carb... Isn't it some post about trouble with this carb ... ?

[jean-yves]

no, I've a 28, not a 27

but when I've tried last week a 30 Dellorto PBH carb, the same effect append...

[Paola]

maybe everybody overread the fact that you are running a squish clearence of only 0.7mm

[jean-yves]

Yes, that's what I was thinking about too for a moment, that's why I went to the machinist to make a spacer between the head and the cylinder to increase the squish clearance to 2,2mm...

I've tried the engine with this spacer, in same conditions; ( it was less powerfull with low mode ), and despite that it seized too (

what squish clearance do you advise me ? 1,2mm, more ?

Bearbeitet 2. Mai 2005 von jean-yves

[bodybuildinggym]

did you ever try another ignition? may be that the "igntion time" changes in different rpms. like an ignition with variable timing which is out of control :plemplem:

what squish clearance do you advise me ? 1,2mm, more ?

1,2mm!!!

Bearbeitet 2. Mai 2005 von bodybuildinggym

[jean-yves]

no, i've not yet tried another ignition..., but now I've a P200 engine on my VLA1T, I will take it on it :grins:

maybe you're right, we'll see

I'll try it this week-end...

and what ignition timing do advise to me ? 17 degrees are specified by Malossi with original cylinder/head, but with more compression ( and heightened port timing ) do you think I've to reduce to 14/15 ?

Bearbeitet 2. Mai 2005 von jean-yves

[cäpten]

no, i've not yet tried another ignition..., but now I've a P200 engine on my VLA1T, I will take it on it  :grins:

maybe you're right, we'll see 

I'll try it this week-end...

and what ignition timing do advise to me ? 17 degrees are specified by Malossi with original cylinder/head, but with more compression ( and heightened port timing ) do you think I've to reduce to 14/15 ?

<{POST_SNAPBACK}>

maybe a stupid answer but as it works in high speed and not when its slow

maybe there is not enough air going through the metall you put over the air wheel well my english is not that good but i hope you get it anyway.

[bodybuildinggym]

and what ignition timing do advise to me ? 17 degrees are specified by Malossi with original cylinder/head, but with more compression ( and heightened port timing ) do you think I've to reduce to 14/15 ?

<{POST_SNAPBACK}>

17° without any probs

try 17° and then step by step earlier but always listen to your engine

amazombi has 21° on his Polini with 18PS and he is known for his his long highway trips with full throttle. Only the 5l Petrol tank can stop him

[jean-yves]

maybe a stupid answer but as it works in high speed and not when its slow

maybe there is not enough air going through the metall you put over the air wheel  well my english is not that good but i hope you get it anyway.

<{POST_SNAPBACK}>

don't worry with your english, mine is not very good too :grins:

the temperature conditions for the test :

here for the moment the weather is dry, 20°c...

I've HP4 fans on my lightened PK flywheel ( less powerfull than PK original ones )

I've always try it without the engine door, exactly as you can see in the pics below

and a Proma flywheel cover... do somebody have used it ? I don't know if it is good ?

the speed for the test is 40/50 km/h I think, no more, I do not have a tacho...

the road is hilly all arround my house...

Bearbeitet 3. Mai 2005 von jean-yves

[jean-yves]

17° without any probs

thank's

try 17° and then step by step earlier but always listen to your engine

sure

amazombi has 21° on his Polini with 18PS and he is known for his his long highway trips with full throttle. Only the 5l Petrol tank can stop him

:grins:

[jannek]

Looking at the thoughts others had about your problem i´d like to say that your squish width of 0,7mm doesn´t HAVE to be a problem, this is a lot dependent of WHERE you measured that squish. If it was only at the outer side of the squish band and then enlarging to for example 1mm at the inner side of the squish band it should be okay. This is also dependent of your compression ratio, but in your case it should not be the problem because your problem is at LOW revs.

Another point I´d like to mention is about the powercurve of your exhaust that was posted. This curve (and all others of the smallframe exhaust test) were taken on a motor with ROTARY VALVE. In my opinion, this is the only reason for a power drop like this (which was still more extreme at the other version of the SIP-Exhaust). At the point where this power drop occurs, the intake resonance is the inverse of the exhaust pipe resonance, so they work against each other.

Because you don´t ride a rotary valve, this drop in power also should not be your problem. Ever been on the Dyno with that Setup?

I don´t think your power curve would look like the one above.

Also if I wasn´t able to tell you where your problem is, I hope I was able to help telling you where it should NOT be.

At the moment i have no idea, maybe I´ll have tomorrow.

Good Night, jan

Bearbeitet 2. Mai 2005 von jannek

[jean-yves]

no, i've not been on the Dyno with this setup... I can't go so far from my garage for the moment :grins:

what is strange to me is that the engine do not heat at all and do not seem to such too much air on the stand boot...

[jannek]

I just calculated your actual MSV with your Setup... If your squish clearance is 0,7mm also at the INNER side of your squish band, this IS at least part of the problem. Assuming you did not modify the Malossi-Head, your actual geometric compression should be around 13,5:1. With this setup your MSV would be around 25 m/s at 5000 1/min which is still okay, rising to completely mad 40+ m/s at 8000 1/min :plemplem: . This is the second Time Bomb of your motor...

BTW: Last Year I also rode a 28 Mikuni on my Malossi, but jetted on the dyno I had the first drop in peak power with main jets larger than 300! 250 was my first attempt but was MUCH too lean.

And the combination of an astronomic MSV and lean mixture isn´t that good...

Try enlarging your squish to about 1mm at the inner side and fit larger main jets until you feel a drop in peak power. This should help a lot.

Greetings, jan

Bearbeitet 3. Mai 2005 von jannek

[Luccio]

his squish has been already raised to 2,2mm....

Bearbeitet 3. Mai 2005 von Luccio

[jannek]

I read that. I did not say, it is the problem, but part of it. At least it´s not rideable very long like this. Raising the head but keeping the mixture too lean is not sufficient. And a squish of 2,2mm doesnt work any more at all.

jan

[Luccio]

I know that he has some difficulties to find needles and needle jets for his TM28 ... :grr:

Bearbeitet 3. Mai 2005 von Luccio

[jean-yves]

@jannek :

no, i've not modified the head...

wow, i've to learn better mathematics... I've calculated only 11,5:1 with this setting

when I tried a 270 (the bigger i had at this moment in my pocket), the engine knocked, do not get high revs... but you're right, i've tried it only with the 0,7mm clearance, my second time bomb... :grins:

I'll retry to put a bigger main jet when I'll have the good squish clearance...

Luccio is true, it's not quite easy to find another needle here. French shop are provided by Bihr Racing, but nobody can help me to find the product reference of another needle/jet for my carb...

I've a 5DP39, do you know what else can I use ? ( less lean in the begining part of the acceleration )

Bearbeitet 3. Mai 2005 von jean-yves

[Olli ETS]

Luccio is true, it's not quite easy to find another needle here. French shop are provided by Bihr Racing, but nobody can help me to find the product reference of another needle/jet for my carb...

I've a 5DP39, do you know what else can I use ? ( less lean in the begining part of the acceleration )

<{POST_SNAPBACK}>

A 5DP39 indicates a Mikuni VM28 type, right?

Some information can be found @ Mikuni Topham.

A .pdf file with the tune up parts Mikuni Topham Carb Parts .pdf.

Regards Olli

Bearbeitet 3. Mai 2005 von Olli ETS

[Luccio]

I think this link is better but I still don't know which needle of the series 5 can replace its 5DP39...

http://www.sudco.com/catalog105/056-060.pdf

nevertheless the 5F12 seems to be the richer needle you can find the class (A) of the series 5...

Bearbeitet 3. Mai 2005 von Luccio

[jean-yves]

@Olli ETS :

yes, my carb is also called VM28 by mikuni

there are only original parts in my carb exept main(180->250) and idle(15->30) jet

[jannek]

@jannek :

no, i've not modified the head...

wow, i've to learn better mathematics... I've calculated only 11,5:1 with this setting

<{POST_SNAPBACK}>

I just guessed it, because i´ve got 12.5:1 with a stock head and about 1mm squish clearance. If i´d reduce my squish to 0.7mm, I´d have 13.5:1.

Don´t rely on my calculation, the only sure way is measuring.

About your Needle: I once compared the TM28SS Mikuni of different machines, the Needles of them were 5J25 and 5L19. At least these two you could purchase from any Yamaha-Dealer around.

More Infos about the carbs are on Olli ETS´s Page:

Carbology

Greetings, jan

Bearbeitet 3. Mai 2005 von jannek

[jean-yves]

I just guessed it, because i´ve got 12.5:1 with a stock head and about 1mm squish clearance. If i´d reduce my squish to 0.7mm, I´d have 13.5:1.

Don´t rely on my calculation, the only sure way is measuring.

you're certainly right

I think I've forgotten the curve of the piston... :grins:

About your Needle: I once compared the TM28SS Mikuni of different machines, the Needles of them were 5J25 and 5L19. At least these two you could purchase from any Yamaha-Dealer around.

ok, I've to compare them to the 5DP39 to know which is richer.

if somebody could help me...

Bearbeitet 4. Mai 2005 von jean-yves

[amazombi]

Another point I´d like to mention is about the powercurve of your exhaust that was posted. This curve (and all others of the smallframe exhaust test) were taken on a motor with ROTARY VALVE. In my opinion, this is the only reason for a power drop like this (which was still more extreme at the other version of the SIP-Exhaust). At the point where this power drop occurs, the intake resonance is the inverse of the exhaust pipe resonance, so they work against each other.

Because you don´t ride a rotary valve, this drop in power also should not be your problem. Ever been on the Dyno with that Setup?

Good Night, jan

<{POST_SNAPBACK}>

wouldn't subscribe to that. it is a time honoured rumour that rotary valves are notorious for their narrow and possibly even erratic powerbands, but time honoured or not, a rumour it is. the curve of the sip pipe, (and a number of other pipes) has been checked against curves of reed valve engines, and the curves are similar enough

[jean-yves]

first, thanks to everybody to share its experience in English .

that helps me enormously...

to summarize, before begin again my tests, I must :

- increase squish clearance to 1,2mm

- put 17 degrees to the advance

- find a richer needle and to buy main jets until 300...

( and change my piston as soon as possible )

- try another ignition ( i've already forgotten it )

other ideas on the origin of my problem ?

others questions :

- do you put oil on Ramair air filters ?

- do/can I modify engine cover to have better cooling ?

Bearbeitet 4. Mai 2005 von jean-yves