Coolant leaking from front of engine, behind clutch cover

[millenium7]

Alright we're getting somewhere. I managed to find a 1990 model being wrecked 133,000km on it. Inspected the water pump and it runs smooth with no discernable play so I paid for it. Also got an idler and tensioner which feel fine so whatever is in the best condition will be assembled onto the bike, along with the old timing belt after I carefully inspect it. Gates T325 is attainable but not easily, its not a part that any supplier has in stock in Australia (that I can find anyway)

The LHS coolant pipe (guessing this one goes to the oil cooler) on the donor housing has snapped off. What's the best process here? I'm guessing carefully drill it out with an endmill, clean up the bore then press fit a new brass pipe in? I've not had to do this before so any assistance with what specifically to buy in what diameter and how to flare it would be much appreciated
Since the water pump o-ring also can't be attained i'll have to clean it up as best as possible and then use sealant, unsure what sort of sealant to use for this as i've never had to touch coolant systems outside of changing gaskets or hoses

And finally the LHS camshaft housing. Is that gasket actually critical or is it mostly a spacer? I can't attain it from Honda so initial thoughts is just to RTV it and re-use. Else anyone know the thickness? and i'll DIY a new gasket
And the seal? Is that typically re-usable or again should be replaced? Was not leaking before

 

[John OoSTerhuis]

That early model ST’s water pump will not work with your ‘95. The internal crankcase breather on all other years vents out the front of the case through the water pump housing. The vent hose connects to a nipple on the lower right corner of the housing, leading up and between the cylinder banks to connect to the nipple under the right side of the air cleaner housing. The first year models have an external breather (black odd-shaped box) near the rider’s right knee, and these models’ water pumps don’t have the ‘through-port’ and would just cover/block the ‘95’s crankcase breather port. Sorry…

John

 

[millenium7]

The housing looks the same and has 2 hose fittings just like mine. I'll compare closely
It's quite common in Australia for year models to be slightly off so it might actually be a 91 donor bike. I'll inspect carefully

Would there be an obvious visual difference?

 

[Roger]

I fitted an equivalent cam belt rather than the Honda product - a Triumph part - if that helps. https://www.davidsilverspares.co.uk/ST1100X-PAN-EUROPEAN-1999/part_196364/

 

[millenium7]

Do you have a triumph part number? That's still listed as a ST1100 part with Gates as the manufacturer so i'm guessing Gates T325

..... kind of ridiculous, manufacturers should be mandated to post specifications of parts instead of forcing arbitrary OEM part numbers and hiding behind corporatism, so that when they decide not to offer parts anymore they can still be manufactured and attained. Ideally (but hey, gotta consider those precious profits after all....) they should be freely downloadable STEP files so any CNC or 3D Printer can replicate parts as necessary and even design alternative and better parts. Wishful thinking I know...

 

[Roger]

Gates T325 is what you want. There are sites that will confirm it's the correct fitment, such as here on Amazon.... https://www.amazon.com/Gates-T325-Timing-Belt/dp/B002RPYZSO
I'm being blocked from accessing Aussie sites because of my current location. - So over to you!

 

[John OoSTerhuis]

The housing looks the same and has 2 hose fittings just like mine. I'll compare closely
It's quite common in Australia for year models to be slightly off so it might actually be a 91 donor bike. I'll inspect carefully

Would there be an obvious visual difference?

Yes, it should be obvious. A picture would help but if it has ports for the oil cooler AND the crankcase breather you‘re good to go. My info is based on USA, 1991-2002 models, inclusive. Good luck and keep us posted.

John

 

[millenium7]

I'm not exactly sure which year model this is, either they thought ahead in 1990 or this is actually a later model one?
I thought it was corroded and snapped off but ur correct they are different, but seemingly not different enough for it to matter. The casing mold looks identical with the only difference being that hole is not drilled through to the water jacket. However I can just drill it, as there is already a recess in place. Note the screwdriver in the picture doesn't drop into the recess, it does on my old one. Otherwise they look identical

Then afterwards I can drill and tap the bore and fit a threaded barb i.e.

 

[John OoSTerhuis]

The pump on the left in your pictures with the undrilled coolant port is for the later year models without the oil cooler (1996-2002 in the USA), IMO. I think your plan to drill and tap the hole and install a nipple would work if you desire to maintain the oil cooler function. I suspect that all years’ pump housings are cast on the same mold and ports etc finished after. Hope this helps…

BTW, most of the failures of ST1100 water pumps of which I’m aware of are a failure of the bearing which is indicated by coolant loss out the tell-tale rectangular weep hole which I’ve marked on your photo. I don’t have a picture of it ‘in-situ’ as it’s a bitch to get a lens on it (and to even see to diagnose the problem).




BTW2: the rust on the impellers would appear to indicate overdue coolant replacement. I know of one case where the impeller blades corroded to nubs that caused a difficult to diagnose cooling problem not identified until the pump was actually removed. Mine were still pristine at 190K.

FWIW. Again: Good Luck! And keep us posted.

John

 

[ST1100Y]

...the rust on the impellers would appear to indicate overdue coolant replacement...

Likely the bad habit of using/topping off with regular tap water instead designated permanent coolant...
The electrochemical corrosion can raise havoc ...

 

[millenium7]

There is some corrosion in the pipes, i've seen worse that still ran without a leak for a very long time

I think the doner bike had a new belt fitted fairly recently before it ended up sitting, as the tensioner on the doner bike feels very good. Almost new though some outside corrosion from where it has been sitting. The idler however did feel good but after several rotations (filing/sanding off the corrosion from where it was sitting) it has just a slight bit of play in it, though still better than my original that was on there. I'm not sure what's an acceptable level of play to run or if it should be completely solid and buttery smooth like a new bearing. I'm not changing the belt and I have no intention of putting another 100,000km on the bike but it would be good to know what to expect. If it's highly likely to go downhill very fast I may consider replacing the idler

As for the pump well it's reinstalled on the bike but has not yet been run. For anyone who comes across this thread in future or wants to include this information elsewhere that's more easily accessible, then it absolutely is possible to fit the pipe outlet that is missing and not have to delete the oil cooler. For this I used
- 11/32" drill bit ('R' drill bit is more appropriate)
- 1/8" NPT 27TPI thread tap. This was the only suitable tap size I have
- 8mm (or 5/16") barb to 1/8" BSP. This should be 1/8" NPT but if you can only get 1/8" BSP they will work
- Thread tape or liquid thread sealant

This would ideally have been done on a drill press, but as I only have a small bench one that isn't large enough I had to resort to a battery drill. Definitely not ideal but its all I have

I first drilled a 4mm hole through to the water jacket, doesn't take much to get through. Any similar sized bit will do fine

Then marked off 13mm on the drill bit and went into the housing. The existing hole is approx 7mm so you could go straight to the 11/32 or R drill bit if using a drill press. As i'm just using a hand drill I progressed 7.5/8/8.5mm then finally the 11/32 (which is approx 8.7mm). Then ran the 1/8" NPT tap down 12mm. The actual thread of the barb is only ~9mm so this is plenty
1/8" BSP is not directly compatible with NPT as its 28TPI vs 27TPI. However since its such a short thread and a tapered brass fitting it really doesn't matter, it should easily deform appropriately to seal

Bit of thread tape and it seats nicely

As for the o-ring, this is unobtanium from Honda as well, however if you can source a BS244 or 108mm (ID) x 3.5mm O-ring then its a perfect fit. Ran a bead of silicone to hold it in place and it stayed there nicely

The smaller o-ring is 15.9mm x 2.5mm however the closest I could get on-hand which does fit is a BS114 which is 5/8" x 3/32" or 15.87 x 2.38mm

 

[Erdoc48]

Wow! Well done! Geez, I hope to never have to go in the bike that far

 

[John OoSTerhuis]

Nice job. Congrats!

 

[millenium7]

It starts, it runs, it doesn't leak after an hours ride. What a massive PITA endeavor but if it helps someone else in future with making a different water pump casing fit, then i'm glad to have at least done something positive for the community. Personally I think it would be easier (and cheaper) than doing the oil cooler delete

Also if the water pump rebuild kit ever stops being available, it is still possible to attain the shaft, bearing and seal through a bearing shop. I don't have part numbers but it's not a unique size and is available. However may require some machining to get it the exact right diameter for the impeller. Any half decent shop should be able to machine down the shaft to the appropriate size and press it all back together fairly easily. In my case it was still cheaper to replace the entire casing with a donor bike and modify it but both options are viable

 

[millenium7]

I have a follow up question: If the thermostat is jammed shut, will it cause the bike to dump coolant into the overflow tank, exceed its capacity dump coolant without any visible steam or other overheating signs?

Here's the follow up situation to date: The bike has been fine and no issues except for today when I stopped the bike at a pub and came back to see a small puddle on the ground near the rear of the bike. First thing I checked is for any water near the front of the engine, its dry so it's not the water pump
I also noticed after a bit more riding and being stopped at a traffic light that it was very hot, just about into the red and starting to trickle a bit of coolant on the ground. I also noticed the fan was not running. I have an override switch for the fan and I need to use it to get the fan going, but still it will quite quickly get into the red in stop-start city riding (which it didn't before)

So on the way home I had a bit of a think and my theory is the thermostat has actually been working fine but just today its decided to give in and is jammed shut. Closing off water to the radiator which then doesn't let the - just recently replaced - water temp sensor to turn the fan on. Bike has gotten very hot and boiled coolant into the overflow tank which resulted in the puddle on the ground

So if this is a likely explanation i'm guessing I just need a new thermostat and away we go. Anyone have a part number for an alternate one? Genuine is quite expensive
At the same time if the bike 'should' have released steam, could the radiator cap be faulty and need to be replaced? Again any alternate part numbers?

 

[DeanR]

Stant 35868/13868new number. orient the little hole facing up 1368
NAPA THM 101/535080
73-80 Civic 1.5L THM010 180 degree
80 Civic 1.5L ATM TG2903 orig. '80 Civic 1.5 engine

 

[Erdoc48]

Interesting observation. I would say if the coolant is missing in the thermostat neck and the overflow bottle is overfilled to the point of dripping on the ground, I’m wondering if the cap is no longer holding pressure and more coolant is going to overflow. Is there any coolant residue in the region of the thermostat housing? I had a similar issue on my 300ZX, wasn’t running hot but I would check the coolant and some was missing in the radiator, Changed the cap and it’s been fine to this day. The overheating (near overheating) could be if you don’t have enough coolant in the system due to it being boiled off. Change the cap first and if this isn’t the fix, then change the thermostat? These are older bikes now, so maybe change both (just to eliminate both as causes)?

 

[millenium7]

Radiator cap had a partial split in the outer rubber seal but didn't see any coolant leak in the area. Have replaced both the cap and thermostat and now the bike does not go above ~33% on the temp gauge when idling for 15 minutes. The fan kicks on and the radiator is very hot to the touch. Previously it was regularly sitting around 60% and the fan was only working intermittently so I'd say it's more likely the thermostat was failing

These are the part numbers I used, as stant and other quoted parts are hard to find in Australia. But Tridon is cheap and sold everywhere
Thermostat: Tridon TT240-180
Radiator Cap: Tridon CB16110

The cap is the same pressure rating and all dimensions to the OEM part but has the little wings on it. No problem with clearance but just remove the 1 little screw that holds the black plastic cover piece in place and bend it out of the way, then you can screw the new cap on. Or just cut 1 of the wings off

 

[Ron]

Is the over flow container full? Is the radiator low?

Check the radiator over flow hose. The hose has been known to split right at the nipple coming from the radiator. Takes a sharp bend there. The coolant will flow out but the split causes the hose to loose the vacuum and will not draw the coolant back to the radiator. If you're lucky, you can cut the hose back an inch or so and re-connect it. I would replace the hose after I got home.

The coolant sensor doesn't sense hot air and won't turn the fan on.

 

[millenium7]

Yeah that hose is split after removing it but the overflow was full. I'll be cutting it back before doing a reassembly.... Again....

Have to say this is by far the worst bike I've ever owned for doing what is essentially basic maintenance. Everything is utterly ridiculously time consuming and difficult to get to. Not one part I've seen has any sort of thought put into maintenance with engineering. Possibly intentional to pay extortionate dealership rates back in the day as changing coolant takes as much time and effort as doing a top end rebuild on most other bikes....