ET: Engine (Twin) Checking the Cam timing on a twin

[oexing]

When you assemble an engine on the bench you could save you a lot of time that day and later as well when you provide marks on cam gears corresponding to marks on the engine case at that same time. Best idea is to have extra light valve springs there and two clocks sitting on the valve stem end by having old caps with 8mm adapters for (digital?) clocks - no need for Sony encoders plus DRO, but I got them anway.
So with zero valve clearance set and clocks zeroed on base circle you turn camshaft of first cylinder for equal readings - in photo 4.37mm MK 2 cam.
So then get the Dremel and mark one tooth closest to some engine case and set a corresponding chisel mark. Once done turn second cam for equal lift and have same marks on gear and case.
So then you can assemble the engine with all components , crank , springs, and all. When dealing with timing gears you have the timing disc on the crank end and by applying the piston stop on spark plug stud in clockwise plus anticlockwise positions readings halved and disc set to zero on TDC you then get crank back to 4 degrees BTDC for rear cylinder, idler gear already pushed into tight mesh in both cam gears, and in this 4 deg set you get the half time gear out and try all 5 slots for best mesh with the mainshaft key and slip it onto crank end. The first camshaft was aligned with its marks of course before for equal lift at 4 deg.
For front cylinder you turn the crank forward for - ah- 410 degrees ? - that would be 406 degrees (-4) on the disc? - hope I did not mess this up at late night writing.
So in this crank position the front cam gear at Dremel/chisel marks aligned should be put into mesh with idler gear nicely. When it is out a lot by a half tooth you´d decide on pressing the cam out of the gear and try better.
I was lucky with all Andrews cams so somebody else will better tell about how to go with some out of synch cams driven by idler gear, some jig would be used for this job I think.
With alignment marks on gears and case you do not care about hunting gears at all, the timings can be checked any time later, unless you get new cams and gears so you´d do fresh marks on these parts.

Vic

Vic

 

[greg brillus]

Are they alloy pushrods Vic.......?.......Cheers.

 

[Freebird]

Hi guys

Thanks for all of your help.

Today I checked both cylinders and found it very easy to get the DTIs directly onto the tappet adjusters so I didn’t need to disturb much at all.
I found the front pot to be bang on, but the rear has both valves at the same lift at close to TDC, so it’s about 4 degrees out.

I think that's one tooth of the cam gear? There are 48 teeth, so 360/48=7.5 but it's running at half engine speed so 7.5/2 = 3.75 degrees?

Cheers

Glen.

 

[Freebird]

I hope this photo comes out ok..

 

[oexing]

Yes, certainly alu pushrods, 10x2mm wall, I was quite underwhelmed finding massive steel rods as originals. Alu is great for fabricating any lengths you want for your engine, the pressed in steel ball ends are no big deal to make. Just you assemble the engine differently, no way to drop them through the adjuster thread. So before you put on the head , drop the rods onto the follower cups and then the head on, a bit of wiggling of the shrouds is needed.
I had photos here before, showing offset shroud seal recesses in engine case by one millimeter at least, not aligned to the follower cups. This obviously was never corrected and it is the root of the problem why 10mm rods will rub somewhere in the pushrod shrouds .
For this I made eccentric seal holders glued into the recesses with o-rings in them. I would not recommend the old style square rubber seals , a pig to shift when you want to push down the tubes or pull them up in top end jobs. Also an o-ring will better cope with any angles of tubes when having compression plates or other manufacturing flaws. So in my cases I shortened the shrouds to end above the recess step inside as I cannot push them down when having them offset to align with the follower cups. But then, no need for pushing down in assembly here, there is enough wiggle in my seal holders plus o-rings to care for it.
Basically these alu tubes should be allright for 8000 rpm in a Vincent, even more. Remember in R 100 RS with 70 hp at 7000 rpm they had them too, at twice the length. Maybe stainless tubes like in link below could be nice, lighter and possibly stiffer in bending loads. So you get better heat growth in an all alu engine, half way between alu and common steel rods.
One tooth out in cam timing is still 7.5 degrees out in valve timing, I´d think. So better have this optimised. All numbers in valve timing refer to crank degrees unfortunately.

Vic

stainless tube 10x9mm

 

[greg brillus]

Be interesting to see how you make allowance for tappet adjustment.......as pushrods will expand as per the engine.......zero clearance cold might not be advisable........any stock Vincent I always set the adjusters with a tiny amount of up/down play anyway.......the tappets do open up as the engine heats up........our roller cam set up, the exhaust opens up quite a bit when hot, not so much in the inlets.......our pushrods are 5/16" hollow chromoly tubes with hardened ends pressed in.......just a little more load on ours than stock........springs have about 140 lb seat pressure.......not a massive amount for a roller cam, but our valve train parts are very light.

 

[oexing]

Tappet clearance with alu pushrods has to be tested in use. I would not think it will be much as length is not a lot compared to Horex postwar or BMW /5 , /6 ,/7 types alu pushrods at twice the size. See the BMWs are all alu engines too and they live with around 0.15 to 0.25mm play cold. So in case I find that clearance in hot state goes to zero I can do some controlled clearance by first setting for nil play and then undo one flat on the adjuster - or whatever I feel it needs. Pushrods may grow less than the cylinder and head as they sit in shrouds in plain air but sure I am unable to tell what valves do in this business to clearances. What do you think about thin-walled stainless pushrods like in my link above ? I like the better heat growth as the steel standards cannot cope with growing rest of alu engine ?
In the postwar Horex Regina 460 special I made an alu cylinder and certainly kept the standard alu pushrods. With a hot engine I see a bit too much clearance really, so I´d rather have more heat growth but don´t see any chance when having alu already .
I love roller followers but typically they add some weight in the valve train. So curved followers would be better for very high revs. But then a Vincent is not the high revving bike anyway, limits are found elsewhere. The prewar Horexes and the 1935 Guzzi got roller followers, crowded needle bearings in there my modification as you will guess. Plain bushes will not last long and never did in the past. Manufacturers never decided on crowded needle bearings then, too expensive possibly their view on this.

Vic

top is alu Horex postwar 400, next is BMW /5 stainless (heavy) , then Vincent steel and bottom my alu with ball ends pressed in.

prewar Horex roller followers modded for needles:

Guzzi prewar standard left side:

Horex 460 special alu cylinder: