260 high head temp... need help

[jimmybrie]

Hi, I'm running a rebuilt 92 260 (did it myself, used to build engines, 3rd 260 I build, been reading on this site for more than 2 years)

Setup is:

- 15 hrs on motor
- Early 260 block
- Top pinned mahles
- Original one piece exhaust plate
- 4 diverter hoses cut 1/4 inch shorter (1/8 top and bottom)
- 1/8 fender washers but hoses are not T'd together
- 5/16 dump hole connected to a 3/8 hose
- Injectors cleaned by brucato
- Merc digital box with A48 chip
- 35 cc heads
- BR8HS
- filled #2 cavity
- intake plate angle cut
- crankcase cut 0.045
- fuel pressure 40# and stable at WOT
- 91 octane gas with splash of ACES

Head temps runs high (180 at WOT and 160 cruising)
Gauge has been checked with water boiler for linearity and accuracy and his mounted in stock merc hole.
Unfortunatly I don't have water temp gauges on the heads
Piston crown reading tells it's running hot too. 2 top holes seems to be the hottest
Running it richer won't bring the temps down, but it will run pig rich at idle and low speed, getting on plane I can hear it's running very rich.(So it is definatly richer when I adjust the pot) Did a mark on trimpot (which was previosly set at 102) and I'm now almost 1/8 turn CW farther then my mark.(I know this is a lot)

Water pressure is 20# at WOT and should be I think 13-15# so this makes me wonder if I have a water flow problem? (restriction) Engine has been running same 20# pressure since rebuilt (06/2010) so there's no wood chunk in the holes that came after . Before rebuilt don't know, engine has been sitting there for 5 years (use to be my father's engine who's now in another world). EGT's are stable and I don't see any sings of water in the exhaust or on plugs so cracked chest pumping in the system should not be the cause.

I have a bare block here and was looking at it and if my understanding is correct the dump communicates with the bottom holes comming from the water jacket so enlarging the dump would increase water flow out of the engine? If pressure doesn't drop means that I have a restriction before the plate right.

I know that dry stacking is the best way to control water flow and temp but just want to test things before I pull out the power head for winter and check everything.

I put the most info I could...

Any help would be greatly appreciated

Thanks in advance :thumbsup:

[Jay Smith]

Jimmy ,
If you are having heat problems with only 1 and 2 the drivers on the ECU are suspect to be weak... The ONLY thing has something to do with only 1 and 2 is the ECU drivers. A 260 ECU has but 3 drivers one driver that fires 1 & 2 one that fires 3 & 4 and last one that fires 5 & 6...If you had another KNOWN good ECU you could simply switch over it could answer allot of your questions...

Just my guess,

"Be who you are and say what you feel....
Because those that matter...
don't mind...
And those that mind... DON'T,WON'T OR WILL EVER
MATTER !!!"

Jay

[jimmybrie]

Yes I have another ECU that is know to be good. I'll try it...

What about the water pressure? (20#)

Thanks

[h2oskiier30]

Had that problem with mine. Drystacking is a solution. I also plugged one of the two dump holes in the adapter plate, and it worked well. Neither is a solution without pulling the powerhead, though.

[jimmybrie]

Plugging dump holes in the plate? You think water is circulating too fast? If I understand correctly that system, plugging holes in the plate will increase water pressure and slow down water circulation. Is that what you mean?

Thanks

[Jay Smith]

Don't close off water flow path or the water pump is toast, call me in the AM @ cell # 1 281 798 3150


"Be who you are and say what you feel....
Because those that matter...
don't mind...
And those that mind... DON'T,WON'T OR WILL EVER
MATTER !!!"



Jay

[h2oskiier30]

What I mean is that the holes in the adapter are so big that the water is dumping out the adapter before it can cool the motor. And yes, plugging one of the large holes (just one, NOT both) it will build more pressure and push more cooling water out across the heads instead of free-flowing out the adapter plate. Plugging only one of them also still allows cooling water to flow across your water pump. I've run two separate 260's this way for the last 3 years, and never had a problem with a water pump showing any signs of melting yet.

[sschefer]

If you don't find it in cooling or the ECU then pull the heads and check the squish. Too little and you'll heat things up and it will be rich on the mid range when you try to cool it down with more fuel. The opposite is true if you have too much squish. You'll have a rich idle and a rich top but the mid will be fine. Actually that's just the extremes on both ends of the spectrum.

If it is squish then you might just get away with a thicker head gasket.

Sorry if this sounds crazy, but I just finally got my squish problem straightened out and I created a lot of the same symptoms that you have along the way. Hey Chris...140 compression is the ticket.. Thanks for the tip.

[jimmybrie]

Thanks for your help but on these motors squish is only determined by gasket thickness and deck to piston height. Both of these are stock. Even if you shave the head it won't change squish...

Thanks

[us1]

At WOT 20# is not unheard of if you are running around 100 MPH of more. I too would be looking at the ECU. If you close up the thermostat washers a little the heads will run cooler but I think you have a lean problem that needs fixing.

[stvhelm]

with your water pump are you running the newer 3/4 water tube or the older 1/2 water tube? the smaller tube tends to let the engine get hot during extended high rpms. also make sure the rubber grommet is in the pump housing and base gaskets are not blown out

[jimmybrie]

I think I run a 1/2 tube but remember it's running too hot even when crusing... About the grommets, IMO any leak and/or restriction from the pump to the block would not give me 20# at the exhaust plate. Leak or restriction before block = pressure drop. Someone correct me if I'm wrong...

Thanks for your help

[jimmybrie]

For now I think to main path I'd like to look at is the weak injector driver (bank 1&2) I'll try another ECU when I have a chance, pretty busy these days. This idea comming from two main guru's on this site means that it's something that had happened in the past. I'll just take a look at all 6 piston crowns again and see.

The other thing I'll check is my water pressure gauge accuracy (which I've not done yet), maybe my 20# is a 16-18#...

Thanks everyone I'll let you know how this evolves.

By that time any other ideas will be greatly appreciated

[sschefer]

Thanks for your help but on these motors squish is only determined by gasket thickness and deck to piston height. Both of these are stock. Even if you shave the head it won't change squish...

Thanks
You are correct that you that you cannot change the physical charateristics of the squish band without a thicker or thinner headgasket or deck/piston height. However, shaving the head and raising compression does change the way the squish band functions. The higher compression pushes the fuel in the squish band further back towards the edge of the piston and that does affect both head and piston temps.

If nothing else works, this is where I'd be looking. There are couple of well written pages about this in Gordon Jennings 2 stroke tuners handbook that prompted me to look at it. In my case it was my problem but it very well may not be yours.

[jimmybrie]

Thanks Steve sounds logical that compression can affect the way squish works but the thing is a lot of people here are running 34 and 35 cc heads on 260's without having that problem.

Talked to Jay on the phone today about several things concerning that problem and I'm pretty sure we figured it out. It's about water passages in the block from what I remember when assembling the engine there's a problem there from factory but it's been 3 months and I'm not sure. Don't have time to check it today but I'll check it maybe tonight and let you all know with pictures if this is my problem.

Thanks all:thumbsup:

[jimmybrie]

Check my water pressure gauge for accuracy: 20psi = 20 psi with other gauge

After

Following phone talk with Jay I removed the divider plate to find out if all divider plate to water jacket transfer holes were free of restriction because I remember seeing some pluged hole when I built the motor. Thought that it was for temperature equalizing thats why I didn't payed much attention.

Jay look I knew I had some pluged holes, seems like sillicone from factory.216265216266

Problem is it's on #3 and #5 so it doesn't explain my temp gauge reading

I removed it anyway following your advice that 12 holes must be opened

But look what I found on the port side and please tell me if you think this could be a problem:
216268216267

Looks like the holes were not drilled deep enough. (but not sure if it really restricts cause it ends on an angle in the jacket)

But I cleaned them anyway and will try to find time to test it on the water shortly. But would like to know your guess? Did you had any problems with that type of holes?

It was a not that simple operation to seal everything so I don't get debris at the wrong places. (in the motor & between base gaskets), but it went good.

Thanks