Welcome, Guest
Username: Password: Remember me
  • Page:
  • 1
  • 2

TOPIC:

1978 KZ750 TWIN - Blown Head Gasket? 19 Jan 2019 06:45 #797070

  • Patton
  • Patton's Avatar
  • Offline
  • KZr Legend
  • Posts: 18640
  • Thank you received: 2098
A leak-down test injects air pressure through the spark plug hole to pressurize the combustion chamber.

Can perform a poor-man's leak-down test by introducing compressed air into a spark plug hole and listening to where it escapes from the combustion clamber. This may be done at TDC or any other cam positions where both valves are fully closed. Top dead center (TDC) is when the piston is at its highest position. An easy way to tell TDC is by alignment of the T mark with the case mark when viewed through the timing window.

May introduce a spurt of compressed air by using a rubber cone-tip blow gun (rubber air nozzle) held into the spark plug hole. And of course keep holding it in position to keep air from coming back out the spark plug hole while listening for escaping air at other places. The air compressor should not be running while listening because the noise will likely drown out any sound of escaping air. Or just use a portable compressed air tank.

Air heard escaping from exhaust port indicates exhaust valve not fully closing (perhaps too tight clearance or damaged valve or valve seat).

Air heard escaping from carb intake indicates intake valve not fully closing (perhaps too tight clearance or damaged valve or valve seat).

Air heard escaping from crankcase breather indicates loss of compression past rings into crankcase (perhaps worn piston rings or cylinders).

Air heard escaping from head gasket area indicates loss of compression past head gasket (perhaps due to a blown head gasket).

A leaking valve may sometimes be resolved by adjusting the clearance to within specs.

A leaking head gasket may sometimes be resolved by torquing the head fasteners when the engine is stone cold (such as after sitting overnight).

Good Fortune! :)
1973 Z1
KZ900 LTD

Please Log in or Create an account to join the conversation.

1978 KZ750 TWIN - Blown Head Gasket? 19 Jan 2019 23:09 #797126

  • DoctoRot
  • DoctoRot's Avatar
  • Offline
  • Sustaining Member
  • Oh, the usual... I bowl, I drive around...
  • Posts: 2543
  • Thank you received: 664
What gasket are you using? all gaskets are not created equal. Kawasaki recalled their early head gaskets for these bikes. Here is some info passed on from a member here

Scirocco wrote: Just some recommendation DoctoRot for your engine rebuild.
Only buy the head gasket part #: 11004-1267, the green one
It´s the last and best cylinder head gasket for the 750 twins

A little gasket history :
11004-071 => 11004-078 => 11004-1055 => 11004-1267
11004-071, recall campaign in June 1976
11004-078, the red one with black middle section
11004-1055, light brown, comes with the first LTD model
11004-1267, the green and the best for the last LTD model



Full story and source but only in German language.

www.z750twin.de/zylinderkopfdichtung.htm

Please Log in or Create an account to join the conversation.

Last edit: by DoctoRot.

1978 KZ750 TWIN - Blown Head Gasket? 19 Jan 2019 23:18 #797127

  • DoctoRot
  • DoctoRot's Avatar
  • Offline
  • Sustaining Member
  • Oh, the usual... I bowl, I drive around...
  • Posts: 2543
  • Thank you received: 664
Other things to consider when assembling:
make sure the chamfer on the oil holes in the head and cylinder (where the dowels go in) is smooth and not sharp at all, and lube the o-rings and dowel hole. Its possible to cut the o-ring when plopping the head down.

You should re-torque the head after the first heat cycle. and i always check it again 100 miles later as sometimes you don't really get it hot enough on the first cycle.

Also I had a bike i flipped last year burn oil like crazy and i finally traced it down to someone stuffing foam in the breather tube. make sure your breather is unobstructed.

Please Log in or Create an account to join the conversation.

Last edit: by DoctoRot.

1978 KZ750 TWIN - Blown Head Gasket? 24 Jan 2019 18:02 #797446

  • Jessmansimon
  • Jessmansimon's Avatar Topic Author
  • Offline
  • User
  • Posts: 21
  • Thank you received: 0
Ok guys. I got the head gasket (the exact one shown in the picture. Greenish tint) and put it on successfully. Torqued the bolts to spec, and followed service manual for camshafts.
Now when I fire it up, vacuum gauge for carbs is reading HALF of what it used to read. So vacuum is LOW. It also seems to be firing strangely.
I thought that maybe I put in the camshafts backwards, like on the wrong stroke (overlap, instead of compression) so I changed them to the next TDC, but STILL have low vacuum and strange firing.
I thought I noticed when I took the cams off first that the exhaust shaft was a little behind compared to the intake shaft when at TDC. (arrow on intake was aligned with cylider head, while exhaust arrow was at a slight angle downward. Service manual says to make sure they are both LEVEL with head. Should I be eyeballing that little behind to get it back to normal? Also, when i put the camshafts on exactly like the manual calls for, one lobe on cylinder two is pressing slightly on the intake valve at TDC. Is this normal? could the sprocket on the shaft be slightly off? The bolts do not seem like they could be moved. What is causing the loss of vacuum?
I do not have access to a leak down test. I actually do not have a compression gauge either, but will get one if necessary for this problem to get it running right.

Please Log in or Create an account to join the conversation.

1978 KZ750 TWIN - Blown Head Gasket? 24 Jan 2019 19:27 #797450

  • Jessmansimon
  • Jessmansimon's Avatar Topic Author
  • Offline
  • User
  • Posts: 21
  • Thank you received: 0
I have since researched and found that TDC is the same position piston wise, so switching the camshafts was kind of a waste of time. But still, there is something not right about the camshafts and I cannot figure it out. Is this an engine where both pistons rise and fall at the same time? I did not try this with the head off, so I will check tomorrow by holding a light in the spark plug hole and turning the crankshaft. It might help me figure out which cylinder needs intake valve open first and vice versa.
Piston 1 would have to have exhaust valve open first after TDC for release of combustion, correct?

Please Log in or Create an account to join the conversation.

1978 KZ750 TWIN - Blown Head Gasket? 24 Jan 2019 19:42 #797451

  • DoctoRot
  • DoctoRot's Avatar
  • Offline
  • Sustaining Member
  • Oh, the usual... I bowl, I drive around...
  • Posts: 2543
  • Thank you received: 664
follow the manual directions exactly. Make sure you put in the intake cam first and pull the chain so there is no slack when you install it. then count the teeth. If the tooth count is correct the exhaust should be level with the head, but don't worry if its not spot on. Do not set cam chain tension until after you install the valve cover.

The crank is a 360 phase so the pistons rise and fall together. it has wasted spark so as long as your at TDC when timing the cams you will be fine.

Please Log in or Create an account to join the conversation.

1978 KZ750 TWIN - Blown Head Gasket? 25 Jan 2019 08:49 #797473

  • Jessmansimon
  • Jessmansimon's Avatar Topic Author
  • Offline
  • User
  • Posts: 21
  • Thank you received: 0
Thats the thing. I definitely followed the service manual to the "t". Pulled chain taut, installed intake first, counted to 32nd link and exhaust cam was level just like it said.
What causes low vacuum pressure? I thought it was improper valve timing or an intake leak. I can just tell something is off as well, the bike moves a lot more when idling (shakes).
The vacuum was at spec before I took the head and cams off. I even checked ignition timing, and its spot on. Any feedback would help. I am getting super frustrated. I'm not sure I should ride it to a shop to do a leakdown test.

Please Log in or Create an account to join the conversation.

1978 KZ750 TWIN - Blown Head Gasket? 25 Jan 2019 08:56 #797474

  • SWest
  • SWest's Avatar
  • Offline
  • Sustaining Member
  • 10 22 2014
  • Posts: 22348
  • Thank you received: 2599
Sounds like the counter balance timing is off.
Steve

Please Log in or Create an account to join the conversation.

1978 KZ750 TWIN - Blown Head Gasket? 25 Jan 2019 10:46 #797483

  • DoctoRot
  • DoctoRot's Avatar
  • Offline
  • Sustaining Member
  • Oh, the usual... I bowl, I drive around...
  • Posts: 2543
  • Thank you received: 664
with out a compression test or a leak-down test its impossible to say if its not getting enough compression. You can get a cheap compression tester at any auto parts place. since you didn't go into the bottom end its not the counterbalancer.

Please Log in or Create an account to join the conversation.

Last edit: by DoctoRot.

1978 KZ750 TWIN - Blown Head Gasket? 25 Jan 2019 11:16 #797488

  • Jessmansimon
  • Jessmansimon's Avatar Topic Author
  • Offline
  • User
  • Posts: 21
  • Thank you received: 0
Ok so i re-fired it up today, and found out that at a very low idle, say 1000 rpm to 900rpm, the vacuum is low. About 4cmhg too low. but when i give it gas or the idle is higher, say 1500, and when it comes back down from a rev, it will hold at spec for a second or two and then come back down. Im thinking maybe the air idle is somehow too high. There's only a fuel idle screw, but I'll mess with it to try to get it to sound better.
So, I'm gonna go with what i feel now and say that its good to go. If any problems present themselves I'll be back.
Thanks for a ll the help guys. RIDE ON!!

Please Log in or Create an account to join the conversation.

  • Page:
  • 1
  • 2
Powered by Kunena Forum