Failure analysis head gaskets

edq

Joined
Apr 15, 2024
Messages
7
Age
69
Location
Trail B.C.
Hello to all. I recently acquired a 93 ST1100 for $ 300. Hideous rattle can paint job. Owner said it was likely a blown head gasket. Got it to my shop. Compression was only 125 across all cylinders, but after I checked the timing(way off) and the belt ,it still runs ok. Took it out for a shakedown run, noticed the temp gauge was cycling up to hot the right down to normal. Once home ,I ohmed the fan motor ;wide open circuit. Hooked 12V right to the fan ,nada. I can assume the heads overheated on the previous owner and took out the gasket around the cooling passages. Explains a lot. But a cheap fix for a really nice bike. Just waiting on a gasket set and fan motor, all coolant drained and blown out. Haven't ridden an ST since 2008. Nice smooth bike,like a lightweight Goldwing.
I couldn't fathom why the head gaskets would fail. Not a common problem on this motor.
 
When you did your compression check - was the engine warm, all spark plugs removed and more importantly, did you hold the throttle fully open?
 
Sounds like the typical problem with the coolant overflow tube to the surge tank deteriorating and leaking. The tank will appear full but over time fluid does not transfer or get returned to the engine as it cools as the hose leaks and can't develop vacuum to pull the coolant back into the engine. A large air space develops in the engine and radiato and cooling becomes erratic. I can't ever remember seeing a head gasket failure on a ST1100 - Uncle Phil may have or John O. A St1100 runs very cool almost too cool when in motion, it will cycle the fan if stopped for a while.
 
Thanks for the replies. DC motors should have an ohm value,terminal to terminal of 10-20 ohms . This one is dead. The compression check was done engine warm and wide open throttle ,all plugs out. Not a big deal, just waiting for parts now.
 
With that compression test results i would fix the cooling system issues than do the co test on the cooling system to see IF you have a head gasket issue.
 
Im kinda skeptical about the head gasket failing. Participating on various ST mailing liSTs and forums since 1994, I can’t recall any reports of failed head gaskets in either an ST1100 or an ST1300. I have heard of the occasional burned exhaust valve as well as cracked cylinder heads (coolant leak) among the 1100s, I’ve also never heard of a head gasket failing the same way on all four or multiple cylinders on any ICE equipped vehicle.
 
If the temp gauge is erratic,the ground connection may be compromised. The main ground is connected to either a bolt that holds the folding grab handle on the left side or a bolt to the pannier rail on the left side. Check to make sure that connection is clean and tight.
 
I'll post pics once I get the heads off, not starting until the parts are here. Thanks for all the replies.
 
tnbill said:
With that compression test results i would fix the cooling system issues than do the co test on the cooling system to see IF you have a head gasket issue.
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the head gasket has to be real bad to show up on a compression test . A leak down test and or a blue water test would confirm .
 
bdalameda said:
Sounds like the typical problem with the coolant overflow tube to the surge tank deteriorating and leaking. The tank will appear full but over time fluid does not transfer or get returned to the engine as it cools as the hose leaks and can't develop vacuum to pull the coolant back into the engine. A large air space develops in the engine and radiato and cooling becomes erratic. I can't ever remember seeing a head gasket failure on a ST1100 - Uncle Phil may have or John O. A St1100 runs very cool almost too cool when in motion, it will cycle the fan if stopped for a while.
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Totally agree. Mine never goes off full cold unless I get stopped or the ambient air temp is 85 or higher. I thought it might be a stuck thermostat but everyone on this forum seemed to say this is normal so I never swapped it out.
 
bdalameda said:
Sounds like the typical problem with the coolant overflow tube to the surge tank deteriorating and leaking. The tank will appear full but over time fluid does not transfer or get returned to the engine as it cools as the hose leaks and can't develop vacuum to pull the coolant back into the engine. A large air space develops in the engine and radiator and cooling becomes erratic. I can't ever remember seeing a head gasket failure on a ST1100 - Uncle Phil may have or John O. A St1100 runs very cool almost too cool when in motion, it will cycle the fan if stopped for a while.
Click to expand...

The coolant sensor does not sense air bubbles in the system, hot or cold. If there is air in the system, the gauge needle will be very erratic. Check the coolant level in overflow tank. If it is full, check the radiator. If it's low, there probably a split in the overflow hose (usually on the bottom) right where the hose connects to the radiator. If you're lucky, you can cut an inch or so off the hose and reconnect it. That 'll let you do some more trouble shooting.
 
A possible better way to diagnose this would be to provide some low pressure air to the spark plug hole on each cylinder individually, with the piston in the cylinder under test at TDC on the compression stroke. Now listen for air flow from the intake, exhaust, crankcase (via the oil cap opening) and finally the radiator neck. In the latter case watch for bubbles. You want to use just enough air pressure and flow that the engine doesn’t try to turn over.

if you hear air flow out the exhaust, this suggests a bad exhaust valve or valves with too little lash. The same applies if you hear air escaping in the intake. Air flowing into the crankcase might be due to worn rings. Only bubbles in the coolant would implicate the head gaskets. It’d be quite extraordinary if both were bad.
 
Well folks, got the old bird back running. Pulled both heads , bores are remarkably good for a bike with 175K km on it. Lapped the valves and replaced the stem seals, There was an ungodly amount of torque on the R hand side head bolts, the L hand side was normal. Now I have 140-150 psi on all 4 cylinders. Good enough for what I need. It was nice to work on a steel frame bike. I had a Yam FJ09(aluminum frame) that was much more congested to do the valve service on. I was going to take the engine out of the ST1100 and stick it in a micro truck, but this bike is too comfortable to hack up. Thanks for all the comments. Dismantling pics attached.
 

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edq said:
Well folks, got the old bird back running. Pulled both heads , bores are remarkably good for a bike with 175K km on it. Lapped the valves and replaced the stem seals, There was an ungodly amount of torque on the R hand side head bolts, the L hand side was normal. Now I have 140-150 psi on all 4 cylinders. Good enough for what I need. It was nice to work on a steel frame bike. I had a Yam FJ09(aluminum frame) that was much more congested to do the valve service on. I was going to take the engine out of the ST1100 and stick it in a micro truck, but this bike is too comfortable to hack up. Thanks for all the comments. Dismantling pics attached.
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I just noticed you are in Trail BC. I've spent a lot of time in your area. My Uncle lived in Rossland for many years and my Great Grandfather worked in the Rossland Mines. I used to ski on Red Mountain. I own my grandparents house in Northport, WA, just over the border where I still have family on a ranch outside of town. This coming summer my wife and I are taking my two granddaughters to Deep Lake just at the border in WA to stay at the family lake house. I love that country and consider it home to me as I spent every year there growing up. Some great riding up there.
 
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