Briggs Horizontal Twin Timing Issue

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  #1  
Old 05-13-12, 05:32 PM
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Briggs Horizontal Twin Timing Issue

Hello! I have a problem with the timing marks on a Briggs horizontal twin. I have a 16hp opposed twin #402437-0666-01. It has a ball bearing on the pto side of the crank shaft.

I have a manual that tells of two different ways to set the camshaft gear to the crank gear. Is anyone familiar with this?

Help much appreciated!

Ed
 
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Old 05-13-12, 08:18 PM
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Should be a marked tooth on each to line up. What other way do they describe?
 
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Old 05-13-12, 08:36 PM
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Cheese: this is the situation. The manual shows the gear/cog line up method for "plain bearing" set up. On engines with ball bearing set up, the bearing blocks the crank gear, so you cant see the mark. the manual says that there is a mark on the #2 crank pin that you line the camshaft timing mark up with.
 
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Old 05-13-12, 09:57 PM
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Okay, I wasn't thinking of the bearing blocking the view of the gear. Are you having a hard time finding that mark on the #2 crank pin? If you are worried that you have it timed incorrectly, here's a way to double check:

Rotate the engine until one piston is at TDC between exhaust and intake strokes. Rotate it back and forth a little and watch piston vs. valve operation. One valve should close as the piston reaches the top and the other should open just as the piston continues past TDC. As the piston reaches the top, both valves should be at their most closed position. One tooth off, and the valves will close at a slightly different moment than when the piston reaches TDC.
 
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Old 05-14-12, 04:33 AM
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yes, I am worried about correct timing. when you say rock the piston a little bit, how much is a little bit? one inch each way? a little more? a little less?

the problem to me seems to be that EITHER you use the normal gear marks on cam and crankgear, OR you line the camshaft mark with the crank pin mark. the two methods would put the crankshaft and camshaft in different places.

my bearing slides back (i have read it should be press fit and heated to move, and I dont know why this is, but it led me to be able to see the crank gear and cam gear marks and their alignment.)

this all started because I had my engine re-bored, .020 over with a valve job and new pistons etc. and the engine only showed around 55lbs of compression. the valves have checked out ok, and I started looking at timing thinking early or late valves would show reduced compression.
 
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Old 05-14-12, 09:20 AM
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The piston and valves should rock at the exact same moment, whether you rock it 1" or 1/8". I don't recall trying to time a camshaft on that engine, so that's about the only advice I can give... to check the valve timing visually. It should be spot on using one method or the other. I've seen the bearings come off easily too, never caused a problem though.
 
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Old 05-14-12, 05:31 PM
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Ok, I found the answer to my timing question. It seems kind of obvious now. Because the ball bearing hides the crank gear mark, they use another mark on the #2 crank pin for alignment. What I didn't get was that when the engine is rotated, the timing marks on the camshaft and crankshaft gear eventually line up. Its the same timing, just located in two ways.

Still hunting my compression loss. Someone suggested maybe the starter doesnt spin fast enough?

thanks for all help!
 
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Old 05-14-12, 07:49 PM
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Using a compression gauge isn't the best method of checking compression on these engines. A leakdown test is much better. Did you stagger the ring gaps? How big are the ring gaps? Has the engine been run to break in the cylinders and rings? With the valves being done, I assume the faces and seats were ground. Were the valve stems also ground to obtain the proper valve adjustments?
 
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Old 05-15-12, 06:39 PM
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A leak down test sounds good, but I dont have a kit, and the gauge is kind of relative isnt it? Good......ok........poor......? I mean it says some leakage is normal. also, I tried to listen for an air leak at tdc with the engine imobilized and coudnt hear well enough to make a judgment.

I did not do the assembly, the machine shop did. I presume they knew how to put rings in etc.

valves were ground and seated......and re-lapped because of some poor sealing. the valve lash was done, and then re-checked. Actually, I thought once the valves were re-touched, I would crank it over and get great compression. My next attempt will be to verify the bore size and make sure it is in tolerance with a .020 over bore size.

by the way......do you have a spec. on the standard bore size for this engine?

thanks again!
 
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Old 05-15-12, 06:57 PM
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The gauge can tell you if the engine is holding pressure or not but not where it is loosing it if it is.
With both valve closed (TDC allowing for past if compression release is involved) it should hold a certain amount of air pressure. If not, then you listen for air escaping either from the carb/intake, oil fill tube or the exhaust.

Just an FYI, I usually adjust valves, then rotate the engine through several times by hand and recheck clearances. Feeler gage should slide snug, and rocker arms should both have some wiggle in them.
 
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Old 05-31-12, 06:46 AM
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If your bearing doesn't fit properly and a press fit, you might check the bearing number. You need to use a 6307Z and remove outer steel seal.
 
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Old 05-31-12, 07:02 AM
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The standard bore is 3.4375, so just add .020 which is 3.4575. The manual doesn't provide the piston clearance. I just rebuilt my 16 hp. and the manual is vague and misleading. It does not give ring end gap on new rings, just reject size. I rebuild engines of all types and I always use the rule of thumb of .004 on compression ring and .006 on oil. There's the possibility that they may have filed the ring end wrong or not filed them at all and could have broken the ring or rings when they put pistons in. My engine had 120psi on one side and 110psi on the other after rebuild.
 
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