Big Valve Trx lives and breathes

[sanddune51]

At long last, and with a lot of assistance from my son Daniel, I fired up my homebrewed Big Valve Trx868 this afternoon. He took it for a blat shortly after we had finished bolting it all back together, he came back and gave it the big thumbs up. He pronounced it "on steroids" compared to the same machine with just the Fcr41's fitted.

It was all plain sailing until dialling in the Kent cams. It took around 12 hours to get the exhaust cam timed in to 107.5 degrees B.T.D.C. (1.5 degrees retarded,but as good as we could get). The inlet cam took only an hour and a half to set spot on @ 105 degrees A.T.D.C. I think we were in the groove after the first one
The cams were ground on the same lobe angles as standard and it would be no less or more of a job to accurately time up the standard cams. I think this was the tricky part and well worthwhile after the time invested in fitting the valves and flowing the ports. I made my own generator cover and cam chain tensioner gaskets and these are holding perfectly but are a little large at the periphery and detract a little from the look of the engine. I think a scalpel could be used to trim them back in situ. Sorry, no photos as my hands were always oily

I have the usual water leak at the O-ring on the coolant pipe that goes into the head and a mysterious oil leak to trace and cure. After that I'll get back down to the same dyno I tested at before I carried out the work.

I'll report back with the curves and show a "before" and "after" for comparison. I'm really pleased so far and wish every success on those members with rebuilds on the go at the moment .


Mark.

[cobbadiggabuddyblooo]

Looking forward to see how this progresses Mark, and I think it's only justice after the time and effort you have put into getting these valves manufactured that you get to enjoy the spoils of your work first...

It can get a bit infectious , as I'm finding now so I can see why the timing is just that much closer to perfect .... . : so slotting the cam wheels is another thing on the to do list..

[cobbadiggabuddyblooo]

So what would be the reason for the yamaha factory to have the timing not where it works to it's optimum do you think??? Have they allowed for some tollerence when the cam chain stretches ????.. Now I'm fishing Mark to feed my own hunger for knowleage...

[sanddune51]

Coolant leak sorted and now have a sticky/non seating/knackered float needle to sort out. No real worries though, all little niggles that are sent to test our determination . Still hoping to get to the dyno by the end of the week if at all possible.

I couldn't have lived with myself if I had just thrown the cams in where the timing marks lined up best.

I now believe that a higher mileage engine with worn cam chain (like mine was) will be suffering from retarded cam timing. The more the chain has worn the worse this situation will be. As the crank is pulling the cams round (tight side of chain at the front of engine) the wear in each link becomes cumulative and means that the cams will be lagging by some amount (n degrees), which is 2n crank degrees. This is important as the cams are phased to run accurately to crankshaft position expressed as degrees Before and After T.D.C and B.D.C.

The above is one aspect which is variable and unknown and the other is the accuracy or otherwise of the original Yamaha marks on the cam sprockets. I think that Yamaha did their best. That is fine for 99.9% of people 99.9% of the time, but on this occaision, not me. The only way to see how far out your cams are is to check this at stripdown. Or you can bypass this and just make sure they are set properly at rebuild .


Mark

[dandywarhol]

Did you set the timing at stock valve clearances? something is niggling me that Kent specify a different gap for timing but I could be getting confused with VW

[sanddune51]

Valves all shimmed up before fitting head to engine, although valve clearance has no effect on timing of valve fully open degrees. eg. valve will still be at full lift at 105 degrees After Top Dead Centre regardless of valve clearance.(Unless valve clearance is greater than cam lift )
Smaller or larger valve clearance than std only affects duration, eg. smaller valve clearance gives earlier valve opening and later closing.
I set my cams using the dwell method with a dial gauge, so for example if the valve is for arguments sake 60thou before full lift at 95 degrees A.T.D.C. and is then at 60thou after full lift at 115degrees A.T.D.C. the valve is fully open at 105degrees A.T.D.C. as this is the mid point.

115 minus 95 equals 20 degrees, therefore full lift is at 95 plus 10 (20 divided by 2)

My head hurts ,but not quite as much as it did when I was turning the engine over and watching the degree wheel and dial gauge at the same time .


Mark.

[dandywarhol]

Yep, got you - wasn't paying enough attention to the figures. Interesting to note how much earlier the valve starts to open when the clearance is at the minimum - it's one way we used to get Honda kart engines to eek out another 1/8 horsepower in Pro Karts - just that you had to reset the clearances every race!

[sanddune51]

I like it. I've been chasing 1/8ths of a horsepower all over this project, hope I've not been losing halves and three quarters at the same time .


Mark.

[sanddune51]

As a little bit of an update, I've now ridden the bike and I can hardly believe how quick it is. It feels like a motocrosser engine, just so little time as it revs out between each gearchange, almost as if it has a huge rear sprocket . It hasn't its on 17/41 gearing. So I'm really pleased with the power delivery. I have a dyno session booked for Wed 4th Sept and am really interested to see the graphs.

Now for the bit that drags me back down to earth. I still have a significant oil leak that soaked my right boot on a five mile test ride. It's difficult to see where it's coming from. The left side of the engine is completely dry whilst the right side is completely soaked. I have looked at the oil tank and that seems fine, as does the oil pipe that runs up the rear of the barrel to the banjo fitting. I am beginning to suspect the return line from scavenge pump to tank. I just wonder if anyone else has had a similar problem or suggestions to lead me in the right direction?

Cheers,
Mark.

[misterdimwiddy]

Pleased that you are up and running Mark.

Mine revs like a demon in all gears but is on 17/43 at the moment. Dropping to 40t rear so that I am not constantly over revving between gears. Also found myself hanging onto revs between turns at Bedford cos gearing was wrong. Still pulls at 9k but the last thing I want is another full rebuild after my crank episode.

Keenly awaiting your dyno run to see how our motors compare mine having a stock head at the time (same dyno obviously). Now have a split collet for Dremel to finish my own head work.

Oil leak on rhs is a tricky one without seeing it. Oil pump cover gasket or O-rings seems obvious culprit but not easy to get wrong. Scavenge return pipe runs under the clutch cover and enters tank at the rear so less likely to soak your boot; more the rear tyre?!

I'd degrease it as best you can and then run it to look for tell tale signs of leak source. Clutch pivot oil seal maybe though I doubt you had to remove this?

Good luck anyway; I'm sure you'll find it soon enough.

Note - hoping for Brands Indy in Sept so may catch you there.

[coxylaad]

Got any of these left ?

[fung]

Not just a pinch in the rocker cover rubber gasket?
Happened on miss blackie. .... what a mess

[sanddune51]

Thanks for the suggestions guys. I haven't had the time to look at this properly but am now suspecting a leak from behind the water pump. I ordered all the bits and bobs from Yamaha which should be with me at the end of the week.

The way I'm approaching this is by eliminating the most likely (in my mind) causes first, if the leak persists then I'll move on to the next most likely area till I've nailed it .

Mark.

[sanddune51]

Not just a pinch in the rocker cover rubber gasket?
Happened on miss blackie. .... what a mess

Almost spot on .

Brand new £18 "non genuine Yamaha" rubber gasket fitted correctly but leaking like a sieve from the cam tunnel end half rounds. Genuine Yamaha would have been £32. If only I had known .
I just assumed that the aftermarket couldn't get something like this so badly wrong. I have no time to get a new one from Yamaha before Weds so will make the original genuine one do another turn. At least to get the dyno run done.


Mark.

[cobbadiggabuddyblooo]

How did your dyno run go Mark...???? Any guesses on the dyno output??? 93 hp at 7500 and 68 ft/ib at 6100 rpm