KZ305 Blowing their cranks

ZED1015 responded to one of my posts a while back, "The 305 is a hand grenade just waiting to pull its own pin.
They are notorious for blowing their cranks and it's not a matter of if but when."
I have no reason to daught his knowledge of this, but am looking for more information.
I picked up an 82 kz305 earlier this year with around 6,000 miles. I love riding this bike, and out of the 3 bikes I own, it has become the one I ride the most.
Anyone have a high mileage KZ305?
On average, how many miles until they blow?
Any preventative measures I can take?
When it happens, will I crash or be impaled by flying engine parts.

Found this article. read to the end. :whistle:
Steve
www.wemoto.com/news/article/592/the_kawasaki_gpz305

The 305's were renowned for blowing their cranks and for anyone old enough are set in biking folk law just like SOHC 750 Hondas ate their cams and carriers etc.
The 305 was based on the earlier 250 which wasn't a great engine to begin with and the GPZ revamp and overbore pushed it over the edge eventually.
One actually blew up passing my house as the guy was on his way to work.
It went with a loud clatter and he just coasted to a stop a few doors away.
He was lucky as i was out front and heard it when it happened and i was the local bike mechanic with a home shop.
It only took a minute to diagnose so he asked me to price for repair and got his wife to pick him up .
I stripped it to see how bad it was and no surprise the crank was destroyed beyond repair .
The cost of a new one was more than the bike was worth and despite arranging to collect the bike he never came back.
Three years later it was still under a sheet so i eventually Ebay'd the remains and gave the frame a higher purpose by using sections of its tubing as frame bracing on a couple of my 1000's.

The only sohc 750's that"eat their cams and carriers" have plugged oil passages to the cam holders or the associated o-rings were left out


just so yall know

They had issues with top end oiling depending on jets to oil the rocker arms. The CB 350 four had the same problems along with no cam bearings. My CL 350 had two cam bearing/rocker side end covers that would be destroyed if a oiling problem occured. All had high pressure oiling systems. The Cl/CB/SL didn't have a filter. It had a centrifugal filter that would get full of gunge quickly. I loved my Honda but I was happy to find the Z1's had REAL bearings that could be replaced if needed. IMO that with the rest of the features make the Z1/KZ engines far superior to the competters.
Miller was the Honda guy and could make them MOVE but but he admitted that was the major flaw in their design. Eating cams and lunching heads. :whistle:
Steve

seanbarney41 wrote: The only sohc 750's that"eat their cams and carriers" have plugged oil passages to the cam holders or the associated o-rings were left out just so yall know

Wasn't saying that was an intrinsic fault but if a 750 SOHC blew the first thing you would think of was that the cam and carriers had copped it so rightly or wrongly that's what they are anecdotally infamous for just like old brit iron and oil leaks.

There are pro's and con's with a lot of older UJM type bikes.

I've had several Suzuki GS's come through the garage and the 2 valve 1000's, 850's, and 550's were good for 100k miles with routine maintenance. A strong case could be made that Suzuki copied the KZ 900 engine when designing these bikes so the linage is good. The plane bearing GS's such as the 650 and 2nd gen 750 were less durable, particularly with regards to the cranks (due to oiling issues.) The 16 valve 1100's were great engines, and generally very tough, but the cams, rockers, and valve guides were subject to wear. Nothing's perfect I suppose.

Is there a place on the 305 engine a pressure switch could be added?
A friend had a 96 1500cc Vulcan with a similar plastic oil pump gear, which stripped. As soon as the oil light came on he shut down and saved the engine.

In case you didn't read this it could be a plug in the crank being 12mm too long. Replacing it seems to have cured the problem.
Steve
"15/01/18 - I would agree with the content of the article in general although the comments highlighted in red at the beginning are a bit unfair.
I bought one new in 1985, a belt drive model, I put 27,000 miles on it without any mechanical issue, it was ridden hard but serviced regularly with oil changes every 2,000 miles rather than the recommended 3,000 intervals. If oil changes were neglected the strainer that you mention could become restricted.
This strainer was supposed to be removed and cleaned every second oil change, most owners and many dealers did not bother as it involved removal of the clutch side engine cover and oil pump and replacement of the associated gaskets, this was the reason why many suffered top end failure due to oil starvation.
Bottom ends could fail too as an oil gallery blanking plug that was used by Kawasaki could be up to 12mm too long and would partially block the gallery itself which was the main oil feed to the crank bearings. replacement or modification of the plug cured the problem.
Fantastic machine overall, lovely handling, good brakes, excellent economy and that belt drive. I miss mine so much that I have just bought one to replace it and relive my youth."

It looks like my idea of adding an idiot light pressure sensor is not going to work. I removed the oil pressure test plug from the head and attached a pressure gauge. Cold oil pressure at idle was only 1 PSI and 4 PSI at 4K rpm. Once the oil got hot pressure was 1/4 PSI at idle and 1 PSI at 4K rpm. It looks like this is a very low pressure oiling system. Oil still flows out the test port as the service manual says it should.
I'm guessing the crank shaft oil plug is behind the clutch cover. Next oil change I'll check that plug length and pick up screen.