Yamaha 80 Valve Measurement

Dora~Jean · Posted: Sun Apr 15, 2007 11:34 am Post subject: Yamaha 80 Valve Measurement

Well it finally came time to bite the bullet and do the valve clearance measurements on my twin Yami 80's (same engine as the 100, also same as the newer 75/90's). Reviewed the Service Manual one last time (about the 10th) before digging in. It isn't technically difficult but requires some diligence to realign the cam sprockets and timing belt, thought I'd impart some of my experience gained. You'll also need inch-lb and foot-lb torque wrenches.

First, make sure you tilt the engine a bit up so the crankcase is forward of level, this will prevent a substantial amount of oil from coming out of the valve cover when removed (called cylinder head cover). Odd this wasn't explained in the manual, engine #1 a big mess, #2 nice and clean!

When I aligned TDC on the flywheel to the separate plate marking, the cam sprocket built in marks did not align per the manual, 1 tooth off on port sprocket. So I marked their positions carefully before removing the timing belt. I then checked the other engine, exactly the same, sooooo, decided prudent to reinstall exactly as I found them since the engines run great.

Last tip, don't forget there are 2 intake and 2 exhaust valves PER cylinder (in other words, don't just measure the top clearance of each cylinder then go back later and measure the bottom ones...don't ask Embarassed

).

The specs on my engine call for 0.008 +/-.001" for intakes, 0.013 +/-.001" for exhausts. All fell within spec Thumbs Up

, thank goodness. Also checked spark plug conditions and gaps while out, all just fine.

Figure about 2 hours per engine, although 2nd engine went about 50% faster! And by the way, those engines have a great valve cover and gasket design.

Sea Wolf · Posted: Sun Apr 15, 2007 4:27 pm Post subject:

Steve-

Nice report and tips!

How many hours were on the engines?

It seems almost everybody that goes through this check doesn't have to adjust the clearance, a GOOD SIGN!

Joe.

C-WEED · Posted: Sun Apr 15, 2007 8:30 pm Post subject:

Steve: Thanks for the informative lesson.

I have the same engine and have yet to check mine. I have heard it is rare to find one out of adjustment but a good idea to check. I believe they use the bucket shim and purchasing a kit would be required if adjustment is needed. Would not look forward to that.

A few questions of curiosity:

How many hours on your engines?

Did you replace the timing belts? If so what did they cost? I wonder if the cams being one tooth off are to account for any belt stretch? It takes a suprising amount of power to rotate those cams.

I would imagine that the engine is a close tolerance design. Does the manual mention this?

Did you reuse the head cover gaskets? I assume no sealant required?

Manual: Did you spring for the high end factory type? Did you find it online?

Thanks

Dora~Jean · Posted: Sun Apr 15, 2007 11:16 pm Post subject:

I have about 350 hrs on the engines, the mfr recommends check at 400 hrs or every 2 yrs. So I split the difference, boat is 4 1/2 yrs old.

Chris, here are answers to your questions:

Sea Wolf · Posted: Mon Apr 16, 2007 12:57 am Post subject:

Here's an on-lineManual for the similar F90D that includes my 2005 Yamaha F90 Fuel Injected Motor. Most of the information wil;l be the same as for the 75, 90, and 100 hp motors. The 115 has more displacement (+150 cc) and a different computer for the fuel injection and ignition (to the best of my knowledge).

F90D Manual

Full code =

http://www.yamaha-motor.com/assets/service/manuals/2005/LIT-18616-02-86_1014.pdf

We (Sneaks and I) tried to figure out the code system and get access to all the other manuals for the different motors, but were unsucessful. Maybe someone else can do it and share the in formation with us all!

If you like this FREE present, send green money to Mike and Bill's retirement fund!

Gift

Joe.

MOOSE · Posted: Mon Apr 16, 2007 9:32 am Post subject:

Interestingly enough, I just checked the valve adjustment on my twin Honda 40s this weekend. It was the first time I'd ever done this. Oddly, I found all of the intake valves to be a little loose and the exhaust valves a little tight. Not more than a thousand or two either way, but I adjusted them all. The instructions I had said to align the "T" mark on the flywheel with and "I" mark on the engine hanger boss, but I couldn't find a "T" mark on the flywheel at all. So I just aligned the marks on the cam instead. The whole job took about two hours. I hope they don't blow up on me when I crank them over, as I'm really a neophyte mechanic.
Al

Dora~Jean · Posted: Mon Apr 16, 2007 10:34 am Post subject:

Al, the "T" mark on mine is "TDC" (Top Dead Center) and is clearly stamped on the flywheel's edge (on mine).

So, the 40's have adjustable valve clearances? I know the Honda's do in my size. Maybe for some reason the Yami 75-100's are stable enough not to have them(?). Seems like few, if any, need adjustment.

In a few weeks after I get the vacuum fittings for the carbs, I'll synchronize them.

MOOSE · Posted: Mon Apr 16, 2007 3:42 pm Post subject:

Perhaps you can tell me, why does the position of the flywheel matter at all? Isn't the position of the cam what is important in determining the TDC of the piston stroke?
Al

C-WEED · Posted: Mon Apr 16, 2007 11:00 pm Post subject:

Al:

Basically the cams follow and are run off the position of the crank/pistons. If you rotate the crank to TDC and the cams are in time then the marks will all be right there. (normally) If an engine is out of time and you only line up the cam timing marks it might be possible to attempt to adjust the valves but the piston would not be at top dead center. Then when you start the engine and the piston is at TDC the valves would not be adjusted properly to match the piston location.

Manuals follow the procedure as a general practice to: line up the crank mark first and then check the cam marks second. If the marks don't align: you are either not on top dead center, not looking at the right piston/valves, the cam belt has slipped a tooth or the flywheel key has sheared and has slipped. Something is not right and should be investigated before going any further.

Remember this procedure is also used for when the belt has been removed, perhaps engine disassembled and put back together. So to start from scratch. Line crank to top dead center on number 1 cylinder. Rotate cams to close all valves on number 1 cylinder and install belt. Marks should be there. Rotate crank two revolutions (for four cycle event). Marks should again be there with valves closed on the next cylinder in the firing order.

One more good reason for following the basic procedure starting with the number one cylinder is to help the mechanic. Say you are adjusting valves on a V-16 cylinder engine. Every time you rotate the crank two revolutions the timing marks should align on the next cylinder in the firing order. If you know the firing order you can identify the next cylinder and watch the valves close. Watching all the valves on a big engine with two banks can give one a headache.

Joe: Thanks for the online manual. Big help.

Steve: Thanks for answering the questions. Thumbs Up

Dora~Jean · Posted: Sat May 12, 2007 1:14 am Post subject:

Finally solved the mystery on my cam sprocket alignments with the flywheel at TDC.