High oil pressure & Overheating 1

[paddo]

Long story short; My '89 Sportster 1200 recently overheated when I left it idling too long. Ran like a dog when I go back on, coughing & spluttering. Turned it off and oil came spilling out of the carby air filter cover (presumably from the vent hose). Changed oil & filter; cleaned out carby/filter etc. and took it for a run.

Runs fine but since then, engine runs a lot hotter than before and every time I switch it off there is a small oil discharge from the carby air filter and I can see traces of oil that has pushed out of my oil tank cap whilst riding. Any ideas?

 

[BrianPetersen]

You may have lunched a piston. Check compression and leakdown on both cylinders.

 

[dgallup]

Maybe not killed the piston but just stuck or broken a ring. Either way, start with the compression and leakdown tests.

----------------------------------------

The Help for this program was created in Windows Help format, which depends on a feature that isn't included in this version of Windows.

 

[paddo]

Thanks Guys,
I was hoping this wasn't the case as I recently pulled down the whole top end and replaced cylinder rings, seals & gaskets, also replaced clutch/pressure plates & stator. Didn't want to pull it down again but I guess I may have to.

I will run compression/leak down tests first. Thanks again. I'll let you know the outcome when I can manage it.

Cheers, Paddo

 

[dgallup]

Maybe consider something with a cooling system?

----------------------------------------

The Help for this program was created in Windows Help format, which depends on a feature that isn't included in this version of Windows.

 

[pennswoodsed]

Rear cylinder cooling design sub par . And there ends the nice things I can say.
Regards,Ed

 

[MikeHalloran]

If you're lucky, maybe you can bore it out and fit bigger pistons and rings.
If you're not so lucky, you'll need new jugs too.

Mike Halloran
Pembroke Pines, FL, USA

 

[ornerynorsk]

Almost sounds like something's up with the timed breather. Does your model year have it?

It is better to have enough ideas for some of them to be wrong, than to be always right by having no ideas at all.

 

[Tmoose]

How did it run with the fresh top end, before the overheating?
How many miles on the fresh top end prior to overheating?
What was the condition you used to identify the overheating?
How long was the "too long" idling time?

I'm not sure I read a symptom I'd relate to high oil pressure.

 

[drwebb]

Seems to me like the rear cylinder should cool about as well as the front one at idle.

 

[BrianPetersen]

... or as poorly, depending on your point of view ...

 

[paddo]

Thank you all for your feedback.
To answer some questions:
Leak-down test 15% on front cylinder = OK; 40% on rear cylinder = problem
Pulled down top end again and currently inspecting rear piston, cylinder & rings
Next Action:
Hone both Cylinders
Replace both Piston Heads
Replace Rings again
Put together and perform leak down test again................

 

[Tmoose]

How do the cylinders look?
Are you saying you have identified visually that the pistons have physical damage that warrants replacment?

after honing and cleaning for assembly I'd wipe each cylinder bore with a white rag damp with clean motor oil. If it picks up any gray then I need to clean the bores again.

https://www.hastingsmfg.com/ServiceTips/cylinder_bore_refinishing.htm

http://www.enginebuildermag.com/2004/05/cylinder-bore-refinishing/

 

[paddo]

Thanks for the tips Tmoose,
I have not had a chance to get back to it to inspect since pulling it back down. I might not replace the piston heads but am prepared to if there is any doubt of their integrity.
Getting back to your original questions - 1) It ran perfectly with the fresh top end for over 6 months before the overheating incident; 2)Approx. 3,000 miles.
3) Running a lot hotter than previously. I could physically feel it and it was now making excessive crackling (cooling down) noises when turned off after a run.
4) It was idling for about 20 minutes on the side of the highway at night as I used my headlight to get my wet weather gear on. I noticed it started smoking so I just jumped on and took off down the highway in the rain. This is when it was coughing & spluttering and severe loss of power. I pulled into a service station and killed it which is when the oil came spewing out of the carby air filter. I let it cool down for about 2 hours, cleaned it up, then hit the road again. It continued spluttering for about 5 minutes then started running normally again, however at every stop - small amounts of oil would spit out from the air filter and a light stream was apparent from around the oil cap.
When I got the bike back home (350 miles later) I changed the oil/filter to eliminate contaminated/burnt oil. It continued running fine but with the oil pushing past the oil cap whilst riding and the spurt of oil from the air filter when stopped, plus the excessive engine heat. That's the long story.............