Author Topic: Coolant Disappearing (Read 10383 times)

swanitalia · « **on:** May 28, 2015, 09:20:35 AM »

Hello all,

Last weekend I noticed my 250R coolant was disappearing. I've recently redone the head and counter balancer. I lapped the cylinder and head flat and true, cleaned both surfaces with acetone and assembled with threebond 1211 with a 3 day cure time.

I've checked my plug and there are no signs of leaking coolant into the combustion chamber, there's no signs of leaks on the outside of the cylinder. I changed the oil twice that weekend and no coolant was present in the oil. The coolant in the rez bottle keeps getting sucked up, and no leaks are present while idling. The bottom hose is close to the pipe and it looks like it's getting some heat damage so i wrapped another hose around it to protect it.

What could be causing this problem? the coolant is slowly disappearing after long rides. I had to top off my radiator 2 times during the weekend which i rode 20+ hours.

Any help with be great.

jimcarrier · « **Reply #1 on:** May 28, 2015, 09:25:21 AM »

if you are sure that it dont smoke, better check near the water pump hole if it leak

swanitalia · « **Reply #2 on:** May 28, 2015, 09:53:20 AM »

I haven't seen the weep hole dripping while idling, but it could be dripping while i'm riding but.

JesseA420 · « **Reply #3 on:** May 28, 2015, 10:13:11 AM »

it is clearly going somewhere, but as you stated very slowly so its a slow leak which where ever that leak is, it is going to be very hard to notice. since you said u recently did the head, i would start there. maybe it is seeping into the combustion chamber so slow that it is unnoticable on the plug?

swanitalia · « **Reply #4 on:** May 28, 2015, 10:25:09 AM »

It could possibly be a very small leak in the head, i will have to check that. Will i need a new head gasket when i pull the head off? I know it's better to have one and be safe then reusing the current gasket.

Jerry Hall · « **Reply #5 on:** May 28, 2015, 10:50:55 AM »

Clean the bottom of the clutch case around the water pump weep hole and look for signs of leakage after riding. Are you using an aftermarket head gasket or the thin CR250 head gasket?

swanitalia · « **Reply #6 on:** May 28, 2015, 10:56:09 AM »

Jerry,

I am using the cr250 head gasket with threebond 1211. I will clean around the water pump when i get a chance.

Jerry Hall · « **Reply #7 on:** May 28, 2015, 04:50:22 PM »

Quote from: swanitalia;54769

Jerry,

I am using the cr250 head gasket with threebond 1211. I will clean around the water pump when i get a chance.

The CR250 head gasket is not made to work on a head gasket surface that has a sleeve. The sleeve and the aluminum are the same height at room temperature when the head gasket surface was machined or lapping was done. When the cylinder is up to operating temperature the sleeve does not expand at the same rate the aluminum surrounding it does. This is why Honda uses the 3 piece metal gasket. The 1211 is a good sealer but it will not fill the void when the aluminum and sleeve are not the same height when the engine is running.

Some guys get lucky and do not have a problem. Some engines do not make enough power to cause a problem. All the OEM ribs on the cylinder sleeves are not located in the same spot.

Sounds like you are one of the unlucky ones so do the necessary machine work on the head and top of the cylinder to get your piston to head clearance, combustion chamber shape and volume right and run the Honda OEM gasket

jimcarrier · « **Reply #8 on:** May 28, 2015, 06:51:04 PM »

#just oring it.... and forget about gasket...

Jerry Hall · « **Reply #9 on:** May 28, 2015, 10:33:24 PM »

Quote from: jimcarrier;54781

#just oring it.... and forget about gasket...

An O-ring seal is the best ways to seal a two stroke liquid cooled head.

That is what I do to them (Machine for 0-rings) but most guys do not want to invest that much money to do everything necessary to an OEM head.

Some of the water ports in the OEM head must be welded up and redrilled to control/simulate how the OEM gasket causes the water to flow through the cylinder.

The combustion chamber shape and squish band will still need to be remachined to get all of those dimensions right when there is not any gasket.

Acorn head nuts and copper washers need to be used to prevent coolant from seeping around the wet head studs.

udontknowme · « **Reply #10 on:** May 28, 2015, 11:18:12 PM »

if it was leaking out the weep hole, even a few drops here and there, it would have dirt and sand stuck all around that area. impossible to not notice

fearlessfred · « **Reply #11 on:** May 29, 2015, 12:49:03 AM »

I think some thermal nuts will cure this.........................j/k

swanitalia · « **Reply #12 on:** May 29, 2015, 07:53:30 AM »

Jerry,

So would using a OEM trx250r head gasket help my problem, the head was reshaped and clearance set. Would the ATC thin head gasket work or should i stick with the trx250r gasket?

Tbone07 · « **Reply #13 on:** May 29, 2015, 10:14:54 AM »

I tried out the 3-piece metal gasket trick as a cheap way of bumping up compression. Started leaking coolant almost immediately.

Definitely get that head machined for o-rings

Jerry Hall · « **Reply #14 on:** May 29, 2015, 11:28:51 AM »

Quote from: swanitalia;54797

Jerry,

So would using a OEM trx250r head gasket help my problem, the head was reshaped and clearance set. Would the ATC thin head gasket work or should i stick with the trx250r gasket?

The ATC or the TRX gasket should make sealing improve but you will be compromising detonation prevention and the performance benefit from a modified head provided the head design was right for the CR 250 gasket.

If the piston to head clearance was set with the CR250 single thickness metal gasket, the piston to head clearance will be excessive with any gasket that is thicker than the CR 250 gasket. You will lower the compression with a thicker head gasket but you will loose the effect of the squish band in controlling detonation.

Lets do the math on a typical modified 250 head.

Let us use the following specifications as our baseline

Bore 66.5 mm
Stroke 72 mm
CR250 OEM head gasket .25mm thick
Piston to head clearance 1.00 mm
Clearance volume 17.2 cc (Volume in the combustion chamber with the engine assembled with all gaskets and the piston at TDC)
Geometric compression ratio 15.5:1

The OEM TRX 250R head gasket is approximately 1.4 mm thick.
The OEM ATC 250R head gasket is approximately 1.0 mm thick.

If we remove the OEM .25 mm thick CR250R head gasket and install the 1.0 mm OEM ATC gasket:

Piston to head clearance increases to 1.75 mm.
Clearance volume increases to 19.9 cc (Volume in the combustion chamber with the engine assembled with all gaskets and the piston at TDC)
Geometric compression ratio 13.6:1

If we remove the .25 mm thick CR250R head gasket and install the 1.4 mm TRX OEM gasket:

Piston to head clearance increases to 2.15 mm.
Clearance volume increases to 21.35 cc (Volume in the combustion chamber with the engine assembled with all gaskets and the piston at TDC)
Geometric compression ratio 12.7:1

Squish clearance in excess of 1.27 mm on an engine of this size reduces the heat transfer from the piston to the head and the squish velocity to the point the head becomes less effective in controlling detonation even though the compression ratio is reduced.

Squish clearance less than .75 mm on on an engine of this size will usually allow the piston to make light contact with the head and make jetting and ignition timing very sensitive.