Honda ST1100 Section => Honda ST1100 General Questions => Topic started by: NovoJeff on August 16, 2020, 10:31:31 PM

Title: I am Struggling with Cooling system leak
Post by: NovoJeff on August 16, 2020, 10:31:31 PM
I need some help with my cooling system. I think I have narrowed down where I have a coolant system leak. Under the carbies there is a fitting that closely resembles a thermostate housing, but it is not the thermostate. This housing has a steel pipe comming from it. My leak is between this housing and the pipe. I have managed to remove a small bolt holding the pipe in place. between this housing and the steel pipe is what honda call a pipe seal.
Has anybody ever replaced this seal? Does the pipe unscrew from the housing or does it just pull apart. Please see attached pictures. The point of the screwdriver is where the seal is located.

Title: Re: I am Struggling with Cooling system leak
Post by: Brock on August 16, 2020, 10:42:45 PM
Looking at the parts break down, it looks like it should just separate. It may take some soaking in a light oil and a bit of heat to make it happen. Years of galvanic action can glue stuff together.

https://www.westcoastmotorcycles.com.au/partFinder/fiche/honda/2000/st1100a-st1100/water-pipe#next (https://www.westcoastmotorcycles.com.au/partFinder/fiche/honda/2000/st1100a-st1100/water-pipe#next)
Title: Re: I am Struggling with Cooling system leak
Post by: NovoJeff on August 17, 2020, 08:52:27 AM
I checked the same drawing and its not very detailed. my thoughts are if it just pushed together would it hold the water under pressure? The s bend shape of the pipe means it cannot be removed without literally removing the entire front of the motor. Not just the timing gear but even the front cast block all this mounts into. I'm hoping someone has separated these 2 components before and can tell me if they maybe screw together with the seal between? The drawing of the seal is not too clear.
Title: Re: I am Struggling with Cooling system leak
Post by: NovoJeff on August 17, 2020, 08:57:10 PM
I have a fix but its also a big warning to others. This whole thing started when I accidently removed the fitting located below the carbies thinking it was the thermostat housing due to the way it looks. Its not, its where the water enters the engine after cooling. The thermostat is elsewhere. Never ever ever touch this fitting unless its leaking. By removing the 2 bolts and cracking the o'ring seal it also resulted in movement which affected another seal between the waterpipe and this fitting. (See picture 1) To replace this has been an absolute nightmare. The waterpipe is made of steel and cannot be removed at all from the bike without removing half the front of the engine regardless of all below attempts. You can however get some extra movement by removing the bolt holding it in place. This bolt is located in front and above the oil filter (see picture 2) again it was designed not to be removed without half the engine missing. To get a 20mm bolt out of a 12mm space I had to undo as much of the waterpipe bolt until its length meet the casting in front then hacksaw it in half, then remove the remaining bolt with longnose pliers. This gave me just movement to pull the pipe and fitting apart exposing a rubber seal that was hard, brittle and no longer capable of keeping coolant under pressure (see picture 4). The seal is another part not stocked in Aust so found one online and about 2 weeks from the UK so I ordered 2 of them today just in case. I did a test run of the re install process. I knew that the bolt I removed needed to somehow be replaced so I manufactured a new one from a SS304 M6 bolt I had (see picture 3) you can see how much bench grinding was needed but the bolt has the smallest head for a spanner to just keep a grip but just enough thread to comfortably hang onto and still be installed in a restricted area. ). Luckily this bolt can be short as it does not need to be torqued and is purely to hold the pipe in alignment. If I had left the original part in place I would not have needed to go to this trouble BUT if it was leaking then this long process is easier than removing half the engine. Im hoping to have this ready for its maiden start up in about 3 weeks.
Title: Re: I am Struggling with Cooling system leak
Post by: RobP on October 01, 2020, 05:08:41 PM
I hope that you got your bike running and all is OK. I am currently restoring a 1995 ST and I know exactly what area you are talking about. I wanted to replace the o rings at that housing and could see that to remove the bolt holding the lower pipe required the removal of the water pump.
I have decided to remove the pump as the condition of every other o ring I have seen has been poor. The timing belt also needs to be replaced if it has reached 100,000 kms or has unknown history. Water pump is no longer available and the moulded o ring was ex Japan and took weeks to get here. The belt is a Gates T325 and is available on ebay.

I see on my bike that the coolant hoses to the oil cooler are brittle and need replacing but they are not available genuine so I will form a plan to replace them with new hose. There is a bleed hose to the thermostat housing that is also brittle.

I now have all the parts required and will be replacing the thermostat (available from SCA or Repco) all o rings with genuine and a set of carby insulators which cost me $70 for a set genuine as I don't want to see this part of the engine again for a very long time.
Title: Re: I am Struggling with Cooling system leak
Post by: NovoJeff on October 02, 2020, 08:23:05 PM
Good on you and hope it goes well. I bought 3 of each extra thermostate and waterinlet o ring's plus I have another water pipe seal if you need and dont want to wait the 9 weeks from Honda Australia. You can have them for what they cost me. Co incidently, I registered the bike today so will be looking elsewhere on this forum for a get together. PM me if you need help or manuals.