RCU Forums - View Single Post

08-21-2010 | 08:16 AM

#62

arnstein

Joined: Mar 2004

Posts: 67

Likes: 0

Received 0 Likes on 0 Posts

From: Kongsberg, NORWAY

RE: YS 170 DZ CDI

The YS 1.70 engine are marvelous engines and a result of excellent engineering, and in pattern one of the few options besides electric. Let us hope that there also in the future will be alternatives to electric, and YS remains one of them, competition benefits everybody. As for any products there are always room for improvements, this is shown by the continous improvements done by YS. 

I think it is important to get a grip on why some of us experiences some issues operation the YS 1.70, it could be that this is entirely due to improper tuning of our engines. This was said in a recent conference I attended:

If a customer buys a product and does not have any problems with the product there is a 50% chance he buys it again. On the other have is a customer buys a product gets problems, but the problem is being taken care of, there is a 80% chance he buys the same product again.

As Bob pointed out cavitation most likely occure within the pump, whether this lead to erosion of the valve seats on a properly tuned engine, I do not know. Cavitation occurs if the liquid pressure falls below the vapor pressure (I think methanol is the most critical ingredience in the fuel wrt vapor, vapor pressure data for methanol obtained from Wikipedia):<table width="521" cellpadding="2" cellspacing="1" border="1" dir="ltr"><tr><td width="15%" valign="top" height="16">

Methanol</td><td width="9%" valign="top" height="16">

</td><td width="9%" valign="top" height="16">

</td><td width="9%" valign="top" height="16">

</td><td width="9%" valign="top" height="16">

</td><td width="9%" valign="top" height="16">

</td><td width="9%" valign="top" height="16">

</td><td width="11%" valign="top" height="16">

</td><td width="9%" valign="top" height="16">

</td><td width="11%" valign="top" height="16">

</td></tr><tr><td width="15%" valign="top" height="16">

P in mm Hg</td><td width="9%" valign="top" height="16">1</td><td width="9%" valign="top" height="16">10</td><td width="9%" valign="top" height="16">40</td><td width="9%" valign="top" height="16">100</td><td width="9%" valign="top" height="16">400</td><td width="9%" valign="top" height="16">760</td><td width="11%" valign="top" height="16">1520</td><td width="9%" valign="top" height="16">3800</td><td width="11%" valign="top" height="16">7600</td></tr><tr><td width="15%" valign="top" height="16">

T in °C</td><td width="9%" valign="top" height="16">-44,0</td><td width="9%" valign="top" height="16">-16,2</td><td width="9%" valign="top" height="16">5,0</td><td width="9%" valign="top" height="16">21,2</td><td width="9%" valign="top" height="16">49,9</td><td width="9%" valign="top" height="16">64,7</td><td width="11%" valign="top" height="16">84,0</td><td width="9%" valign="top" height="16">123,5</td><td width="11%" valign="top" height="16">138,0</td></tr><tr><td width="15%" valign="top" height="16">

T in °F</td><td width="9%" valign="top" height="16">-47,2</td><td width="9%" valign="top" height="16">2,8</td><td width="9%" valign="top" height="16">41,0</td><td width="9%" valign="top" height="16">70,2</td><td width="9%" valign="top" height="16">121,8</td><td width="9%" valign="top" height="16">148,5</td><td width="11%" valign="top" height="16">183,2</td><td width="9%" valign="top" height="16">254,3</td><td width="11%" valign="top" height="16">280,4</td></tr></table>

The normal pressure (sea level) is about 760 mm Hg, from the table we see that the vapor pressure is 65C/150F. So vapor will form inside the fuel system, causing vapor lock at this temperature. For methanol the vapor pressure is highly non-linear with temperature as the graph attached shows.

In my opinion this explain why fans are used in Japan and elsewhere to keep the pump temperature below at least 65C for a successful restart also low fuel temperature is beneficial. On a warm day in Norway (25C/77F) I manage to start the engine again within only a few minutes, however, it runs rough for a few seconds until the fuel cools the pump and all vapor dissapears. Was not able to find any data on vapor pressure for fuel, might be different?

As already referred to by Bob I modified the pump with steel valve seats and furthermore I changed to the "low oil" configuration (crank, cam followers and sub needle). This season the engine has run perfectly and very consistent so far (knock wood). My experience is that these engines runs even if they are tuned outside of the "sweet spot", without experiencing any dead stick. The difficulty in tuning these engines, in my opinion, is the strong interaction between the pump pressure and the HS needle. What is really important is to have a clean transition thru the mid-range. Can this be the reason why some of us, myself included, run in problems and the experts do not? 

Just a thought: What about making a video on how to tune these engine similar to what Bert and Bobby has done in their SmackTalkRC Episode #1 ?

Regards,

Arnstein

Reply Like