Help!! How does one identify when a piston is in the compression stroke?

I'm in the middle of a valve check/adjustment on my 5th gen. I don't have the data in front of me, but a lot of the valves were out of spec. So, I followed the manual directions and removed the cam holders and cam shafts from the rear head so that I could check the shim thicknesses in the valves that are out of spec (too tight, by the way).

Anyway, for camshaft reassembly, the manual instructs one to turn the crankshaft clockwise and align the "3T" mark on the ignition pulse generator rotor with the index mark on the right crankcase cover, and to make sure piston #3 (for the rear) is at TDC on the compression stroke. I've got the "3T marks lined up, but am unsure whether I'm on the compression stroke.

Can someone please advise me????

Thanks!

 

Wait.... did you use paint to mark where the gears mesh before removing the camshafts?

 

No, because you didn't explain it properly!

No I didn't. But, I plan on doing it on the front head. Another confusing thing is that the manual says to paint the cam gears, not where they mesh with the crank, but on each cam's dual gears. Does this make sense? There are two gear disks at the end of each cam that are slightly off (maybe 1mm). It seems like the manual wants us to mark these (see pg 8-29).

Regardless, I've lined up the index lines on the camshafts facing outward, but am not sure if I'm the compression stroke.

 

I know it's not quite clear but you would know just by the fact the index lines on the camshafts are facing outward AND that the crankshaft is on the right 3T mark. An old school way of telling is when you rotate you'll notice it gets harder to turn and then bam it gets real easy to turn.

 

Thanks, Joey!!

 

On a 1st gen I remove the spark plug of cylinder 1 and put a finger on the hole while rotating the crank shaft. You can feel a higher pressure when all valves are closed (compression stroke). From this starting point, rotating instruction lead to the compression of the other cylinders. Not sure it is feasible on a 5th gen, haven't tried yet.

duB

 

I checked my 5th gen valves last night. I've got one intake valve on #3 at 0.003" (spec. 0.006 +/- 0.001). Looks like I have to pull a cam on the rear bank. Bummer. A couple of others are 1/2 a thousanth tight, but I don't think I'll worry about them.

We all hope the valves are OK and some say "forgetaboutit", but they need to get checked. I have 55,000kms (34,375 mi) on it.

 

I like to look at the cut-away view to see the piston's position.... on the bike it is harder. If you use a helper to turn the crank, you can use a wooden dowel into the spark plug hole to see when the piston is TDC - that's when the dowel is furthest out of the hole.

Good luck with the fun.

 

Finally got done checking all the valves, a job I started yesterday. I think it's taken me around 12 hours to check them and remove the cam holders and shafts. This is my first time ever opening up a motor, so it took longer, but I learned a lot so far. Now I know I don't have to remove the air cleaner housing; what a pain in the ass.

Anyway, a problem I've run into is that some of the valves that are out of spec, according to the leaf gauge, could actually be within spec if there were intermediate leafs between the ones provided. For example, for the intake valves of piston 1, the .127mm leaf fit in the gap fine, but the .152mm leaf didn't. Spec for the intake valves is .16 + or - .03mm. Therefore, if my clearance is actually .135 or .145, the valve is still within spec. Another example is the exhaust valve of piston 1. The .254mm leaf fit withing the gap, but the .279mm did not. Spec for the exhaust valve is .30mm + or - .03. What if my clearance is actually .270mm or .275? Then it's still within spec.

Any suggestions? Are these numbers close enough that I should change the shims anyway?

By the way, it looks like stock shims on 5th gen intake valves measure 1.82mm and exhaust valves measure 1.75mm. Some of the shims had these numbers (182 and 175) marked on them. Others did not, which is probably due to the numbers rubbing off.

Thanks!!

 

Since they're still within spec I'd say you can leave it the way it is and get back to it at the next 16K mile servicing interval. It's a real pain in the butt to change the shims and reinstall the camshafts and really, you're not going to get any benefit from making such a minor change. Maybe you will from the fact it won't be off as much in the next valve check but by then there will be possibly other valves out of spec and it's easier to do valve adjustments wholesale instead of piece-by-piece.

 

MAN, you're real brave goin in there removing cams !!

Work very slowly, use an accurate torque wrench, and maintain surgical cleanliness. Turn the engine over by hand when you're finished, and STOP if you hear or feel any resistance because the timing could be off.

Be aware that you can damage a valve when installing cams if timing is not correct.

another way to identify compression stroke is to observe cam lobes since the lobes will be pointing away from the valves on compression.

 

So does it sound like they're within spec? Would they only be out of spec if the .127mm (.006") leaf didn't fit (on the tight side of the spectrum)? I already have the cams off, so if it'd be better to change some shims, it's not a bad time.

Thanks. Before I removed the cams, I felt resistance when turning the motor by hand, but that's probably just the cycle, right? So if I feel MORE resistance, I'll stop.

As far as cleanliness, I've prevented anything from falling in the motor, minus some dust.

 

Hey Jaimev,

Thinking in imperial measurements here - If the min. spec. is 0.005" for the intake and a .005 slides in easy or with a light drag your OK. Even if the .006 won't, your still OK. (I can't get an .004 in one of mine!). For the exhaust side if 0.011 goes in, your good.

When you are turning the motor and feel resistance - it's just compression (assuming your plugs are still in!).

Sidebar - for anyone thinking of doing this...you don't need to remove the airbox, as the manual refers and you can CAREFULLY support the rear of the gas tank, disconnecting two wire connectors and the vent/overflow tubes, leaving the fuel in the tank and the fuel connections intact. I'll post some pictures tomorrow - if anyone cares.

Good luck Jaimiev and thanks to joeydude for the coaching!

 

Squirrelman, wouldn't the cam lobes be pointing away from the valves at two different times? Once on the compression stroke and once between exhaust and intake? My only experience removing a cam is on an inline four with SOHC so I'm not sure. Are the cams on the VFR geared to make only one revelution per all four strokes of the piston?

2 crank revolutions = 1 cam revolution?

 

Thanks, everyone!! Couldn't have gotten through it without your answers and suggestions. Thanks for taking the time.

I guess I'll assemble everything and inspect the valves again in 16k miles. Wish I hadn't removed the cams!! Now I have to wait for new o-rings; although the current ones look like they're in really good shape.

By the way, what a great learning experience this has been. I learned a lot because I'm definitely more visual. I've heard the term double overhead cams many times, but now I'm much more familiar with it. This doesn't mean my motor won't explode when I start it once it's back together. Knock on wood.

 

YOU'VE discovered something else too: it's not very hard to CHECK clearances, but much more involved and challenging to CHANGE them......

 

In regards to determining compression stroke. YOU do this when you install the cams...the piston just goes up and down.

For an engine that's already assembled...you want to figure all this out BEFORE cam removal. The easiest way is to turn the engine over by hand (the same direction it spins when running) and watch the intake cam lobe of the cylinder in question. When the intake cam lobe allows the valve to close, the VERY NEXT TDC on that cylinder will be compression stroke.

One other thing...on a V or opposed engine it's possible to get the separate banks out of synch. For example, if you pull the cams on the rear cylinders and turn the engine over once...the pistons will be in exactly the same place as the previous revolution, but if you time the cams at that point...you will be out of synch with the front cylinder and ignition timing and the bike won't run. If you're in doubt, it's best to pull both valve covers, determine the firing order from the shop manual, turn the engine over by hand and match compression stroke TDC's to the correct firing sequence.

Regarding the two to one ratio of cam to engine RPM, as far as I know, all four strokes have this in common.

The gear driven cams make it really easy to do VC adjustments. Timing cams on cam chain models is tougher. A Vtec is double hard...you must pull the cams, disable the Vtec valves with the special little tool shims, reinstall and retime everything, check your clearances, if shimming is needed pull the cams again, reinstall and recheck, remove and retime once last time to reenable the Vtec lifters.

 

LOL, just a little word of advice, make sure the bike is in neutral before attempting to start it up. I learned that one the hard way after spending all day putting everything together and the bike wouldn't even crank. I almost took everything apart when I happened to notice the green N light wasn't on ha ha ha!!

 

Upon further review, the crank has to turn at a 2 to 1 ratio to the cams or the exhaust valves would be open also on the compression stroke and the intake valve would also be open on the power stroke. Thanks for helping me think this one through Dizzy!:thumbsup:

 

The manual instructs one to install new sealing washers on the four inner bolts of both cam holder As, as well as the o-rings around the two sets of joint collars per head (16 total, I believe). Of course I don't want any leaks, but is this necessary if the motor's never been opened up before and they all look fine?