Engine Removal (Engine Positioning Bolt

[ALPRIDER]

Looking for a bit of help. At 20K my S10 refused to start. A cylinder leakdown test revealed 80% compression loss within 30 seconds. Trying to drop the engine so that I can disassembly and have a look. Here is where the trouble started. My Yamaha dealer could not get the special tool required to remove the Positioning Bolt (P/N 90890-01485) for at least 8 weeks. Being the impatient type I had a machinist make up a tool that I thought would do the trick. Long story short, it didn't do the trick at all. Instead I have now stripped the grooves on the positioning bolt. I have tried a #6 easy out on the 7/16" inner bore of the positioning bolt with liberal amounts of penetrating oil, heat and paraffin and even acetone and ATF mixed together (not at the same time with the heat) all to no avail. I am starting to wonder now if the bolt is perhaps a left hand thread or if it is designed in some way where gripping the ID with an easy out. Can someone who has dropped the engine from the frame let me know if I am on the right track or if there is some helpful trick or tip to get the darned thing out? Thanks very much for your time.

 

[Thrasherg]

I don’t mean to hijack your thread, but i would expect all engines to lose about 80% of the compression after 30 seconds? Piston rings have gaps at the end of the rings, they are only designed to hold the pressure for a fraction of a second. Are you sure you had a realistic expectation to start with? I have not removed the engine from my S10 so cant help with the bolt question, but wanted to point out that I think you had the wrong expectation when you performed the compression test, I am not a mechanic, so could be wrong, but knowing how the seal is created inside a combustion chamber, I could never see the pressure remaining inside the cylinder for more than a few seconds, it would leak around the rings and through the gap at the end of the piston rings, the valves will probably leak a small amount, etc..

Hope someone can help with the bolt question, but before taking the engine apart any further I would try and get some confirmation that your test is reasonable. I think every engine would fail in the way you described.

Gary

 

[ALPRIDER]

Thanks for the quick response, but the engine obviously has low compression issues with sounds of escaping pressure through the head gasket so I don't want to get sidetracked here. The motor definitely needs to come out. Just looking for someone who has direct experience in removing the engine positioning bolt to chime in here in case I'm missing something. The weather is starting to turn nice here in Missouri and would be nice to ride my favorite bike again!!!
Cheers, Bret

 

[Checkswrecks]

If it's not in Greg the Pole's blog, then pm him
https://thetenerist.wordpress.com/2017/03/04/yamaha-super-tenere-xt-1200-top-end-rebuild/

 

[Don in Lodi]

Just posted and removed the same info. I read the whole blog pretty much and he doesn't mention having any problems with any fasteners.

 

[ALPRIDER]

Yes I read Greg's blog and he doesn't mention it. I'll try a PM. Thx.

 

[greg the pole]

Replied. PM notification no workeeee!!

The thru bolt was never touched. The way I understand it, is that it's a locating bolt, nothing else, it lines up the motor. So as it sits from the factor it will stay (or did for me)
Pretty sure I had gently pry it away, once all bolts were undone.

As per write up, scissor jack is a must.
follow the manual.
It's been a while but it should come out, with a bit of coercing.

Did you try heat? The nut is AL is it not?
I sent you all my info in the PM. Holler if you need help,

Greg tP!

 

[WJBertrand]

Wondering if the leak test was done correctly? I don't think you're supposed to shut off the air and let the pressure decay, rather you keep a constant pressure on the regulator gauge and then observe the difference on the downstream gauge while air is flowing. This should be more or less a constant value over several minutes. As stated above, if the air source is shut off. pressure will decay rapidly.

https://en.wikipedia.org/wiki/Leak-down_tester

 

[RonH]

Also the engine has those decompression pins or whatever they are called that could effect readings. I'm not sure how they work exactly, but they somehow effectively lower compression for starting. In 20,000 miles use it seems very unlikely to have an engine failure.

 

[Don in Lodi]

Wondering if the leak test was done correctly? I don't think you're supposed to shut off the air and let the pressure decay, rather you keep a constant pressure on the regulator gauge and then observe the difference on the downstream gauge while air is flowing. This should be more or less a constant value over several minutes. As stated above, if the air source is shut off. pressure will decay rapidly.

https://en.wikipedia.org/wiki/Leak-down_tester

::008:: ::008::
With the cylinder at, and held at TDC, a steady 100 psi in, xx out, gives you the percentage of pressure loss, rings, carbon, burnt valves. I like to see less than 10%, but I believe 20% is acceptable.

 

[eemsreno]

I totally agree with having the leak-down test redone correctly, as stated above it is a percentage of air loss not what leaks off when the air pressure is taken off the regulator.

 

[jbrown]

The auto decompression system opens the exhaust valves slightly under about 500 rpm. There's a mechanism similar to a distributor mechanical advance on one end of the camshaft, with weights that retract the decompression pin as the rpms rise.
It's not clear in the workshop manual exactly when in the cam rotation the decompression pin holds the exhaust valve open (pictures look like the pin is close to opposite of the lobe center), or if it can hold the valve open at zero rpm, but you would need to be certain that the pin is not holding the valve open when you are doing the leak down test.