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TOPIC: TDC below the cylinder height

TDC below the cylinder height 11 Jul 2019 21:48 #807404

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Hello
This us a strange thing I have assembled the bottom end and I fitted one piston and drop the cylinder with no gasket to measure the deck height, on TDC the piston is 49 thousand bellow the deck hight with I and few people don't understand why.
the engine is originally a KZ900 still have the KZ 900 block wich was bored to accommodate the 1260 jugs. the crankshaft is kz so, I know that the J model rods are suppose to be 40 thousand shorter than the KZ but I don't see why would someone have replaced the rods.
any Ideas about it.
I ordered a 5 thous coper base gasket and 43 thous cylinder head gasket which is the thinner I can get to get good compression on the engine.
I grew up riding and fixing all sort of small bike until I inherited A 1977 GS 750 when I was 16, that changed my life completely I love metric bike and I own a few fully working and have some projects.

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TDC below the cylinder height 12 Jul 2019 01:09 #807410

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Take a look at Larry Cavanaugh Website.

cavanaughracing.com/kzdata.html

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TDC below the cylinder height 12 Jul 2019 06:35 #807419

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I know that the cylinder is casted 908 correct for the bike, the crankshaft is correct for the kz 900 engine but we don't get why is getting bellow the deck on TDC.
I grew up riding and fixing all sort of small bike until I inherited A 1977 GS 750 when I was 16, that changed my life completely I love metric bike and I own a few fully working and have some projects.

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TDC below the cylinder height 12 Jul 2019 07:02 #807420

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It's 903. My 1015 barrels are the same as the 903 as far as deck height. Pistons are 2mm lower than the deck. In your case I'd leave it with the larger clearance. That motor must get very hot and tolerances close up as everything heats up. Did you do the squish test when it was last put together That could have been what happened to the valves. Like to see more pics of the valves, barrels and head.
BTW, what's up with the center of the valve stems? Are they thinner, are the valve guides shorter? Is this a drag motor you're trying to put on the street? If so you may have to detune it some to make it last.
Steve
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Opinions expressed by me do not reflect those of the the staff or members
kzrider.com/forum/11-projects/598262-kz-...-will-it-live#672882
kzrider.com/forum/2-engine/597654-poser?start=240#704229

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TDC below the cylinder height 13 Jul 2019 08:18 #807471

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hello
Whell the 909 3nigne I purchased and had issues with cultch basket was making a lot of noise so I opened the engine then decided to undercut the transmission and put a billet clutch basket and MRE single stage lock up clutch.
the crackshaft had a windage tray that I left there. .
the top end was done the pistons were skirting so I bored to 1260 was at 1200, the head was ported and had a 390 and 400 cam over bucket so.
I had another 1400 engine on the side that had ported head with those valves with happen to be Manley and actually are not damaged in fact were made like that for a while to reduce contact with the valve guides, I was told by the guy at pitstop performance.
that other head with came from a 1979 LTD had CM Z6 with 450 lift and titanium springs and under bucket shims thats the reason I am using that head. its going to be a biiy detuned by a fraction.
I intend to use it sparingly on the street and eventually might go to the track on the week-end.
The frame has extended swing arm with a 200 tire and Yamaha R1 front end its a frame up build that I have been working on, since the bike that had the 1400 engine I put a brand new stock engine1015 with only a 4 to 1 dyna ignition jetted carbs and pods.
but after I had that 1400 the 1015 feels like a turtle so I want to have back another blasting fast kz.
I grew up riding and fixing all sort of small bike until I inherited A 1977 GS 750 when I was 16, that changed my life completely I love metric bike and I own a few fully working and have some projects.

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TDC below the cylinder height 26 Jul 2019 16:59 #808206

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hello ok.
seems that the guy that put togheter my engine bottom and measured the piston height made a mistake .
he said I was 49. thou below the deck with no gasket on TDC, Meaning and suggested me to put 5 thou base and 43 thou head gasket as that was going to make 97 thou
and normally I should have between 60 and 80 thou for a good compression.
now I put 5 thou base gasket and in TDC the piston Is a bit out the deck so he made a mistake now I don't know how to calculate that if is going hit the valves .
I am 2 thouover the deck.
I also have 50thou head gasket available and have 10 20 30 thou base gasket but I would hate to have to remove the cylinders again it was a pin in the as to fit it in. any sugestion
I grew up riding and fixing all sort of small bike until I inherited A 1977 GS 750 when I was 16, that changed my life completely I love metric bike and I own a few fully working and have some projects.
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TDC below the cylinder height 26 Jul 2019 17:14 #808207

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Sorry to hear about but you have to bit the bullet. You can add a second base gasket as a spacer to get your deck high.
And you are above the deck high on TDC and not below. This is a total different off topic Situation.

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Last edit: by Scirocco.

TDC below the cylinder height 27 Jul 2019 06:38 #808228

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I know I will have to change the base gasket but what measurement should I be aiming.
I grew up riding and fixing all sort of small bike until I inherited A 1977 GS 750 when I was 16, that changed my life completely I love metric bike and I own a few fully working and have some projects.

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TDC below the cylinder height 27 Jul 2019 09:07 #808241

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You should really use a solid spacer of the correct thickness to set the piston at zero deck height.
Zero deck height is what the pistons compression rating is based on.
Using multiple base gaskets is not really ideal as they are compressable and will result in a positive deck height and a higher compression than desired once torqued down.
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