Dutch MKIII

Hi All.

I´ve taken my MK3 engine apart, the main reason is that it vibrates. There´s more vibrations in the handlebars then on my Triumph T140. I´ve had the bike for about 10 years and it has always bin like this. It had 2 Amal when I got it, then a single Mikuni and now a SU. It had Boyer ignition until early this year, when I fitted a Pazon. All new isolastic´s and a Norvil headsteady. Everything set at is should be and double checked, but it still vibrates. I´ve found 2 things that can cause this. The isolastic´s. When I check the front iso on the right, there´s more play on top then at the bottom. When checking the the rear at the left it´s the opposite. When we fitted the Norvil Headsteady, we had to modify it to make it fit, the whole thing was moved to the left. So the whole engine isn´t vertical in the engine. This can be one reason for the vibrations. The second reason is probably the conrods. There´s 2 different rods!!! The weight difference is 7gram. Is this enough to cause vibrations?

I have asked in another topic (interstate-freshening-t15810.html) about camshaft wear and Jim (comnoz) have recommenden me that I should use oil with ZDDP. I don´t doubt that Jim is right and I will be using better oil in the future. I must admit that I haven´t payed much attention to what kinde of oil I´ve bin using, as long as it was 20W50 or singlegrade from a well known brand. But is the kinde of oil really my only problem? I´ve changed the camshaft twice, in the 10 years I´ve had the bike! When the first was gone, we thought it was just a “Soft” cam from the factory as the story goes. A new standard cam was fitted. That one was replaced with a Magacycle 560-NR. Both fitted with new or resurfaced followers and cam lube. I´ve fitted an oilpressure gauge and yes I know what many people think of that on a Commando. When the engine is cold the pressure goes up to 80psi, but it drops to 20psi when it gets up to temperature and running at 3500-4000rpm. When running stationary it´s just above 0psi. All the commando owners that I have come across who have an oilpressure gauge have lower pressure when cold and higher pressure when hot. My dad´s 750 have 60psi when cold and about 40 when hot. Remember, this is in the northen part of Europe where the temperatures rearly gets much above28-30 degree C. I´ve fitted a new oilpump and had the old one checked, it didn´t make a difference and the old one turned out to be good. I´ve fitted new rockerarms spindles and they do turn the right way around. I´ve also fitted another cylinder head, that also didn´t make a difference. The new head had nothing to do with the oil pressure, but was cracked. When I got the engine apart, I found that the oilpressure release valve were stucked in closed position. This probably explains the high oil pressure when cold, but not the low pressure when hot. The crankshaft was reground and fitted with new bearings, it´s still fit for use. I´ve changed the oil sealing washer (06-6190) on the oilpump whenever I´ve had the primery cover of. I´ve checked the Plunger in the timingscover (06-6199) and it moves freely and seems okay.
Here´s a Photo of the two old cams, the upper one is the first, the lower is the second standard. It´s both the left inlet.

Here´s Photo of the right inlet.

Here´s Photo of the Megacycle cam.


Before I throw a lot of Money in to the engine once Again, I´d like to check everything. So any ideas are most welcome.

Thanks.
Dan Christoffersen

I would check your front mount. The MKIII has a different mount body. Maybe someone put an incorrectly modified front mount on the bike.
Did you compare the steel caps of your rods separately to see where the weight difference is? You can take some weight off them for closer balance. Keep in mind the piston and associated parts are part of the balance equation but 7 grams difference between the rods seems un-necessary.
Those cams look bad! Definitely worth buying good oil and dribbling oil down the push rod tunnels before starting if the bike has sat over the winter or a long period of time.

Wow. The Dutch are a very thorough people and your descriptions are detailed. First off I would say the frame is most likely bent. Has it ever seen a lay-down or accident in the past ? Personally I would not be too concerned with a 7 gram difference in rod weights although others will differ. Those are the worst cams I've ever seen. The oil pressure relief valve being stuck for who knows how long then freed up is a likely reason. Many MK 111's came with poorly heat-treated lobes right out of the factory. The M cam needs to go in for work. Fly me out there to assist , :wink: love Holland !

Have you checked to make sure the pushrod for that valve, is not rubbing somewhere in the pushrod tunnel ??? If the cam lobe on ONLY that valve is worn that much farther down than the others ... "it ain"t the oil "! (IMO) That cam lobe is pushing MUCH HARDER than the others ... to get that valve open. And that is why it is so worn down, and the others are not.

Years ago, I had a 1973 850 motor I tore down (8,414 miles) and it had one cam lobe worn WAY down ... just like yours. (and the other three cam lobes were just fine)
It was bought as a non runner. The PO said it gradually ran worse and worse, so he just parked it. My brother purchased it for $300 ... and gave it me as a present in 2003.

Anyway, after further investigation (and reading the Norton tech digest) I found that one of the cam tunnels had not been machined as "open" as the others. (A common problem with 1973 850 barrels I read.) Additional inspection of the pushrod revealed it had a big scrape where it had been clearly rubbing on the side of the cam tunnel :twisted: :twisted: :twisted: I took a file and a dremel tool and removed just enough metal so that pushrod now had plenty of clearance. I assembled it and now it was the same pressure to open as the others. Teardown and enginneer blue revealed it was no longer rubbing as well.

So ... even though yours is a 1975 MK III, perhaps the same guy machined YOUR barrel, still making the same mistake. Norton were not know for the best "quality control" you know :cry: Just my 2 cents, and worth a check anyway. Cheers.

Do you have the old bearing shells , tp post a photo of the mating surfaces - sounds like they were slack .

No oil pressure at idle , if you sit at traffic lights . Ouch . Shoild be good with correct regrind & shells .

rods should be balanced . end weight both the same .

Look at ISO's as a PLANE / say if bike layed on right hand side - the gaps on the left / top should all be EVEN .
If somethings out of whack / the tube ( Iso ) is ANGLED , diagonally opposite corners will scuff . Throwing the
whole concept into dissaray .

Ideally the bike vertical , the gap would be even each side on all mounts . Best to have it thus .
Rode a Vibrateing commando - footrests and the rest . Beddy Appalling . Looseening the nuts
on the Iso sleeves might get it free to see No Vibes . MAYBE the adjustable Mk III ones youcan back them off ( OPEN )
untill it bounces freely - No Vibes ( bar the 2000 rpm shudder and the Idle Pogo . :twisted: :lol: )

Carefully Levering at each iso , to see if it goes on the rubber , would check theyre not TIGHT .
If it vibrates with a FIVE Thou clearance - You need to align the pins & or set so the triangle of points are all dead on the same vertical plane ,
or at least that the gap is not askew .

I left N-V long before there was anything other than the original Commando model out there. With the original Isolastics, and the 750 engine, there was no vibration in the frame except for a slight shudder around 900 rpm. No tingles, no rattling of frame mounted components. We did have some problems with frothing of the fuel in the carb bowls, because the engine was moving around quite violently, but none of that movement was discernible to the rider. Compared to my company "ride-to-work" 650SS, the Commando was velvet-smooth. As the develpment program matured, I was riding 500 miles a day in around 8 hours, with no vibration issues.

Perhaps when you fit new big end bearings, you might consider using 'Plastigauge' to check the clearances of the bearings on the journals ?

To check rod shells - assemble plain and torque to mostly full, turn on crank, feel for drag then open up and use new razor blade as scraper to remove the witness marks on the soft shell, a little bit at a time, so must repeat a few times to get nice - then put in plastigage to verify what you already can see and feel.

The discolouration on the small ends suggests to me either overheating or else a poor quality oil that is breaking down. I've never seen that sort of staining on an engine that I've put together and oil-changed regularly.

Is it vibrating with the norvil removed (at standstill...)?
with really cold oil, and correct crank/rod clearances, oil pressure goes way beyond 80 psi easily

Since you mention ill fitting head steady and strange measurements at the front isolastic, I'd do a frame inspection. I found some 1/2" steel tubing about 4' long, if I cut it in half, it could be stuck through the isolastic mounts with the frame removed of course and see if you could measure any out of parallel or bad measurements. Otherwise it's off to a frame expert.

If the frame is enough out of specification, I bet the isolastics would not work right.

Dave
69S

I've been though a bit of bent frame to point headsteady nor front iso mount would fit or line up, so i levered and bashed and wedged till could assemble again with reasonable help and assymetric shims at top to have as good a smooth isolating and secure sweet handling Command as any one's un-tamed Cdo. I say just get it to assemble decently to see if you ain't completely happy with it before escalating. I play right up to limits of tire and isolastics stability on my plain Jane Trixie and can detect nothing vibe wise or handling wise out of the ordinary and maybe a bit smoother than the handful of other expert built Cdo's.

30 some years ago before I was enlightened by someone who knew about engine oils I had two cams that ended up looking like yours in just one year in one motor.

I would not consider 20 lbs of oil pressure at idle on a hot engine a sign of problems. An oil pressure gauge on a Norton is a good indicator of the engine's operating temperature. 0 psi at idle means really hot. 30 psi at idle means it's probably really rich and not up to temperature.

I wouldn't think 7 grams difference in rod weight would cause a big vibration problem but matching them and getting a dynamic balance job done would insure the smoothest motor.

It looks like there is a rub mark on one side of the rods small end in your picture. That should never contact the inside of the pistons pin journal. If it has been rubbing then something is crooked. Probably the rod. A bent rod will cause a big vibration problem also.

To get the smoothest bike the isolastics should be aligned. However I have seen them that were quite a ways off and still didn't show any vibration problem.

A Norvil type headsteady is definitely not one of the smoothest units around. Go to a rod end steady and you will like the result. Jim

That top picture the small end looks rough yes so why would it be so ? Pictures of pistons too please. Please fly me to amsterdam to ascertain problem and tour Heineken Brewery again just one more time in life please. :|

Hi All.
Thanks for your replies. I forgot to say that the frame is now at a friends place, he´s going to help me get it straight. He has checked it and according to him, it has had an accident, most likely something hitting it fron the left. He rides Commando himself and has done several Commando frames, hi has also made his own featherbed frame. Frame,svingingarm, front mounting and rear mounting will all be checked. We´ll also check the stearinghead.

I haven´t compared the steel caps of the rods, to see if the 7 g is only in the caps. But I´m going to replace them anyway. Some people say use them, some replace them. I´m going to replace them for peace in minde. A good season and I´ll do 15.000 km. If you´re looking at the Photo of the rods, you´ll noticed that the text are difference, and the Little logo too. These alu rods are maybe 35 years old and have had ??? PO´s, who knows. I´ll probably replace them with Carillo´s, maybe JS motorsport+pistons???

I have just checked both pushrod and tunnels. Neither of them have rubbing marks. But it sure could be that that one valve is working much harder then the others. We checked everything (everything we could think of) last time we put the engine together. We also checked for coilbound and couldn´t see any difference between left and right.
Here´s a Photo of the bigend bearings.


Unfortunatly I´ve never checked the temperature of the engine. 20 psi at idel would be great. I had it dynotested when I was still running the single Mikuni. The tester sayed it was perfect and that I shouldn´t touch the carb. It made 45 bhp on the rear wheel, sounds okay to me. Only Things not standard is the Megacycle cam, Boyer and Mikuni. What do you think?
By the way, here´s Photo of the pushrod tunnel. I don´t have a Photo of the camfollowers, but they look the same. I´ve always pured a bit of oil into the exhaust valves when the bike has bin standing for more then a couple of months. I could fit oversize followers, but I found another cylinder, so will be using that one.


I haven´t tried to remove the head steady, but I noticed that there were more play then what there should be. probably the plastic washers wearing. I´d like to make a rod type headsteady. I´m working as aTig welder, so should be able to make something usable.
I´ve never done 'Plastigauge', but will have a look at that.

I´m not Dutch by the way. I´m Danish. Just living here in NL with my Dutch girlfriend.

Thanks once Again for your replies and please keep them coming. There´s a lot to think about.

Dan

Hi.

I´ve checked the camshaft bushes and found that the driveside has a wearmark. The driveside had 0.2mm play and the timingside has 0.1mm



What should the play be? The workshop manual dosen´t cover this. I have new bushes and are planning to fit them, they then need to be linebored, right?



This is the driveside bush. But is it surpose to sit like this or should it be pushed fully home in the case?

Dan

dantriumph said:

What should the play be? The workshop manual dosen´t cover this. I have new bushes and are planning to fit them, they then need to be linebored, right?
This is the driveside bush. But is it surpose to sit like this or should it be pushed fully home in the case?
Dan

Click to expand...

There should be no play (just a smooth turn) after fitting new bushes and line reaming. The bush must be pushed fully home.

Hi.
Thanks for your help so far. Here´s another question. The TS bearing sealing washer (06-7526) is a tight fit in the crankcases. But shouldn´t it be turning with the crankshaft? There is a slight wearmark on both side of the washer. See Photo.


Dan

Hi All.
I wasn´t planning to take the frontfork apart, but changed my minde when I drained the oil. Looking in the parts manual I notice that there a "Washer" 06-7520 between the Guide Bush and the Oil seal. Andover Norton calles is a "Paper washer" The parts manual sayes I need "1" But 2 oil seals and 2 Guide bush ect. There were no washer in my frontfork. Is this just a simple plain paperwasher/gasket?
Last time I adjusted the ISO's I noticed that when I had adjusted the front Iso, I had a gap of about 1mm between the adjusted and the frame. The Down tubes will be pulled together when tightening. Will standard pre MK3 front Isolastic shims fit behinde the End caps on my MK3?

Dan

dantriumph said:

Hi All.
I wasn´t planning to take the frontfork apart, but changed my minde when I drained the oil. Looking in the parts manual I notice that there a "Washer" 06-7520 between the Guide Bush and the Oil seal. Andover Norton calles is a "Paper washer" The parts manual sayes I need "1" But 2 oil seals and 2 Guide bush ect. There were no washer in my frontfork. Is this just a simple plain paperwasher/gasket?
Last time I adjusted the ISO's I noticed that when I had adjusted the front Iso, I had a gap of about 1mm between the adjusted and the frame. The Down tubes will be pulled together when tightening. Will standard pre MK3 front Isolastic shims fit behinde the End caps on my MK3?

Dan

Click to expand...

There are two types of 'genuine' oil seals: rubbberized bottom and sharp steel edge bottom. Only the last one requires the paper washer to seal.

You experienced the weak point of the MK3 adjustable isolastics: everytime you tighten the iso to the required gap the total length of the iso unit will reduce and therefor the frame lugs will be forced inward when you tighten the central iso bolt. So best thing to do is to shim your 1mm gap with a 1mm washer (left or right side whatever is best for your alignment) on the central iso bolt :!: