engine swap questions

[gs650gt]

hello from the sunny and warm finland!

1) the story
2) the questions


THE STORY

this concerns the gs650g (gm) katana engine = the little kat with shaft drive, 73 hp according to the papers.

I own a gs650gt -82 tourer (also shaft drive, 64hp according to the papers) with > 200 000 kms on the clock so I purchased a -82 oversize gs650gm swap engine from a dutch salvage yard.

I opened and cleaned it and finally mounted it to the frame but the results weren't very promising (heavy oil consumption, terrible heating, oil pressure light "flaming" etc etc... despite of new gaskets+oil seals, good looking clearances everywhere and the oil pressure between given limits when measured...) guess I have to put the old engine back and check again everything the new one during the winter...


THE QUESTIONS

- does anybody know if there's an oil cooler in the gs650 katana? I've seen pictures with and without it...

- any other differences between the gs650gt/64hp engine and the gs650gm/73hp engine? or is the difference just a re-jetting ang and exhaust system trick?

- does anybody know the wear limits for oversize piston sets...or can they just be calculated from the standard measures?

- I have a desperate theory for the heavy oil consumption where the oil escapes from the breather chamber through the breather hose to air filter body and then through the carburetors to the combustion chamber to be burnt and thrown away to the exhaust system. IS THIS RUBBISH ??


thank you for reading this! looking forward to get replies - specially from gs650g kat owners&gurus

 

[Anonymous]

Re: engine swap questions

- I have a desperate theory for the heavy oil consumption where the oil escapes from the breather chamber through the breather hose to air filter body and then through the carburetors to the combustion chamber to be burnt and thrown away to the exhaust system. IS THIS RUBBISH ?

That reminds me...

I know first hand that that sort of thing can happen. I had an '82 Honda Accord hatchback (I loved that car) that was using oil like crazy and the gas mileage was going south fast.

I had long decided to replace the car and trying to get it home for disposal from college I lost nearly 4 quarts of oil over about 200 miles. I left the car sitting at a rest area and called my parents to get me, thinking to get the car the next day.

The next day I brought a new oil supply and started to drive it home with my Dad behind me. About 30 miles into the trip, orange flames leap from under the hood as I pull into a gas station. 8O The forward opening hood blew them right over the windsheild. We quickly got the fire our and after getting it home and pulling the head off we figured out what it was.

I was getting blow-by from one of the pistons and it was pushing air up through the head through an oil drain hole. This oil then travelled through the breather and into the air filter housing. This then drained right onto the heat sheild of the exhaust manifold.

At highway speeds there was enough air to keep it cool, but once it could sit and build up heat I had a nice oil fire going right below the fuel lines. :roll:

I know I'm not much help, I just thought I might tell a story.

 

[SqDancerLynn1]

for that to happen it would be evident becauseinside of the air box and air filter would be coated with oil. Is it?? does it smoke?? could just be that it just needs valve seals or rings

 

[gs650gt]

oil in the airbox?

oil in the airbox?

for that to happen it would be evident becauseinside of the air box and air filter would be coated with oil. Is it?? does it smoke?? could just be that it just needs valve seals or rings

yes, there was some oil in the airbox, but not enough to explain why an just overhauled engine spends one liter motor oil on a 400 km trip... annoying!!

I also expected the airbox and carburetors to contain a copful of oil but no way...

well, anyway, if any oil is drawn to the breather pipe, it is a symptom of problem in oil circulation... oil not returning fast enough from the top to the bottom ??

 

[SqDancerLynn1]

were the rings replaced?? did you measure the end gaps of the rings
It sounds like there is too much blowby in the engine (rings not sealing)
Need to do leak down test to check the condition of the rings, check dealer or your friendly mechanic (need gauges and air supply) to find someone to check it for you

 

[saaz]

Sounds like rings to me (unless the bike is going really badly as well, in which case a holed piston).

It could be a combination of leaky rings (pressurising the crankcase, pushing oil through the air box to be burnt) and oil getting past the rings and being burnt directly in the combustion chamber.

A compression test dry and with oil squirted in the cylinders will tell you the initial story. Get a mechanic or mechanical friend who knows what I mean to do it.

If you are concerned about the breather hose, try removing it from the airbox and put it into a bottle or something for a while and block off the airbox entry for the hose. This will show how much oil is escaping that way. There should not be a lot of positive pressure from the hose.

 

[gs650gt]

were the rings replaced?? did you measure the end gaps of the rings
It sounds like there is too much blowby in the engine (rings not sealing)
Need to do leak down test to check the condition of the rings, check dealer or your friendly mechanic (need gauges and air supply) to find someone to check it for you

like I said, the swap engine was purcased from a salvage yard... it had been there for lord-knows-how-many-years... it had been rebored to first oversize and crashed soon after that (poor fellow!)

I checked and cleaned the motor of course and the piston ring-, piston-to-cylinder- and valve stem-to-valve seat clearances etc looked allright to me, but (as said) the workshop manual contains only wear limits for standard parts, not oversize... that's why I'm not 100% certain about this...

the compression test didn't indicate major leaks (when measured all four cylinders gave a reading around 10, a little oil added > 11). so I'm in a middle of a mystery. the spark plugs were oily allright and exhaust fumes gray.

 

[saaz]

By my Gs1000 manual 10 is within specs. Perhaps the oil rings are not too good (glazed bores, lost tension, broken etc), or really badly worn valve guides, valve stem seals not too good if it has sat around for ages? Valve guide problems are usually most obvious when closing the throttle..clouds of smoke