Engine Timing on a Squarecase..

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mizike77
860 GT / GTS
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Engine Timing on a Squarecase..

Post by mizike77 » Fri Apr 24, 2009 4:55 am

Just about ready to reassemble the motor on my Darmah. Any hints or tips from those that have done it before? Only the top end is off. In the manual it looks like I have to pull the flywheel and the bevel gear plate to line up the bevel gear timing...is this the only way to set the timing? Any tips on piston ring placement?

duck-a-tye
Mariana
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Post by duck-a-tye » Sun Apr 26, 2009 1:47 am

Hi

If you didn't touch the bottom end, (and it was ok before) you won't have to do anything but line up the dots.

Barry

wdietz186
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Post by wdietz186 » Sun Apr 26, 2009 7:45 am

If you have the right side cover off you need to set the vert. cyl. at tdc.The dots on the bevels should be facing you.If not rotate the engine counter clockwise until they do.With the dots lined up on the heads the flats on the shaft will match the position on the lower bevels.It is all very simple really.And yes the intake valve on the horiz. cyl. will be open.

mizike77
860 GT / GTS
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Post by mizike77 » Sun Apr 26, 2009 2:50 pm

dO i have to pull the flywheel and other parts to see the dots on the lower bevel gears or can you see them easily without having to pull anything...?

mizike77
860 GT / GTS
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Post by mizike77 » Sun Apr 26, 2009 7:39 pm

I took off the cover tonight and spun the engine over to lone up the lower bevel gears. I can get the lower dots on the lower gears to line up and face out toward me while the vertical clylinders con rod is up all the way in the stroke. Then i placed the heads oer the studs without the pisons or cylinders mounted to see if the valves were opening properly. With the lower dots lined up and the vertical rod up, the intake valve on the horizontal cylinder was open....is it really that easy? Does it sound like I have it rght? I took pics of it all , i will try to post.


wdietz186
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Post by wdietz186 » Mon Apr 27, 2009 8:59 am

Yes Mike it is really that easy if you didn't take the bottom end apart.It's a pretty simple engine once you get past all the shims and stuff.I would have replied earlier but I was out riding yesterday. Bill

mizike77
860 GT / GTS
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Post by mizike77 » Mon Apr 27, 2009 5:50 pm

HHmmmmm....put it all together today. It went together smoothly with one big problem.Only got 90 compresion horizontal cylinder and only 12 on the vertical. Valves not adjusted properly?

wdietz186
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Post by wdietz186 » Mon Apr 27, 2009 7:20 pm

It appears the valves were at least lapped in, Did the machine shop recut the valve seats? If they were did you or the shop reshim the valves? Lapping or cutting the seats will reduce the opening clearance and if too tight it will hold the valve open and cause aq compression leak.It will also allow too much closer clearance and that can reduce your cranking compression and also allow leakage while running.The openers should have about .004" and the closers about .0015"-.002" Check with the cyl. at TDC

mizike77
860 GT / GTS
Posts: 272
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Post by mizike77 » Mon Apr 27, 2009 7:35 pm

I sent the heads to my local duc shop and they in turn sent them to a machine shop where I believe theey were ground. Then sent back to the duc shop for shimming. I may give it a leak down test to make sure its the valves. I installed new oil orings also. The dowls are the same from cylinder to cylinder correct?

mizike77
860 GT / GTS
Posts: 272
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Post by mizike77 » Tue Apr 28, 2009 10:21 am

Stupid question here...all there is between head and cylinder is the small oil passage way o rings..correct? No large oring or head gasket. Also,it appears that the is a slight gap between cylinder and head. Like the head hasnt fully seated on both cylinders. I s a 20thou gap normal?

MartinMille BANNED
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Post by MartinMille BANNED » Tue Apr 28, 2009 3:08 pm

Mike , take the "O" off and check if the head seats all the way , as you have found out there is no gasket only a barrel base gasket and the oil "O" rings

The "O" will keep the head slightly up and ones the head carbons up this will form a better seal



Cheers Mate
btw; the seat and tank etc was a good buy ;)

wdietz186
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Post by wdietz186 » Wed Apr 29, 2009 6:22 pm

Yes the dowels are the same for both cyls.Make sure they seat fully in the cyl. and have no burrs that could keep the head from sealing. A small gap between the head and cyl. faces is normal.The combustion chamber is sealed at the recess in the head and the lip on the top of the cylinder. Sometimes the bevel tube can cock slightly and hold the head up a bit,I tap the head and tube gently with a soft face hammer before tightening the head nuts.Do the nuts up in three stages 10,20 then 30ftlb. using a cross pattern.

mizike77
860 GT / GTS
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Post by mizike77 » Wed Apr 29, 2009 7:21 pm

I found out why i had no compresion in the vertical cylinder. In my haste to get the engine together I made a careless mistake.I put all my new oil orings on the head and then put the head on the cylinder. Well, I missed the old o ring already on the cylinder. So i inadvertantly doubled up the orings. The issue has been repaired and now both cylinders are reading 80psi. Still low.....im thinking my gauge is bad?

wdietz186
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Post by wdietz186 » Thu Apr 30, 2009 7:46 am

If they are uniformly low I would think it is the gauge Cranking speed will make a difference too.The desmo engines also read a bit lower because the compression helps seal the valves and there is always a bit of leakage at low cranking speeds. That is why the closing rockers have the light spring to help the valve seat when not running.It does improve with use too.

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