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My first foray into not just one but two 1975 RD350's
- Thread starter Vincenthdfan
- Start date
Next door neighbors.
Nice haul.I've had the bikes in my possession long enough now to have gone over both of them with a fine tooth comb.
The runner has cleaned up great, the seat is 100% intact (amazingly!) and the chrome, while not perfect, is very presentable with very small patina spots on the mufflers mostly.
The best part is the parts bike is in such great shape I will NOT be tearing it apart for parts...its way too complete albeit very, very grubby (which nicely preserved the chrome by the way!). I started working on tracking down a title for it and it sounds like I have one on its way from the original owner who last tabbed in in 1991! Another one saved!
How did you track down PO to get a title?
In MD its only $30 for a duplicate title and I have made offers to people if they only filed the paperwork and I"d pay for it + extra $ for the trouble and they all declined. 2 of the 3 bikes are still on fakebook for sale w/ no title
The guy I bought it from was able to track down the original owners son (after I kept pestering him), who as luck would have it happened to be a classmate from high school back in the day.
The son asked his dad to file for lost title in order to get a duplicate...he did and now the new one's coming in the mail. Took a lotta pestering and homework but worth the effort.
For me to apply for a bonded title here in Washington State would have been far more of a pain in the butt than what I went through to research this one.
Regarding jetting....this is why I suspect an air leak.The VM28's and RD's in particular are (in my opinion) overly sensitive to elevation changes. How much change is there from where you got 'em, to where you are? If it's more than 1500... a couple thousand feet, you'll need to rejet the VM's.
Also, you ain't gonna get get much at all below about 4-5 grand... but when they're tuned, and come up on the pipes.... hang on!
Guy I bought it from rebuilt carbs, etc to resurrect the bike and get it running. He did a great job on that, didnt even ruin the original black paint on carb bodies, gave me the original jets and everything.
He did however need to go up on the mains and the pilots to get it running and riding properly. He believed that was because he went to a new Uni brand foam filter over a cage in place of the original paper element filter (which he provided me also). Air box still all intact, lid included...
I sort of have a hard time believing it would make a that big of difference, thus my taking it easy on test ride when I took delivery of them...dont wanna burn a hole or two in the pistons.
Borescope looks good, still see cross hatching.
Eastern S Dakota is about 2000 ft higher than you I'm guessin'?
I'd suspect you'll need to bump them up another size.
And that engine design is pretty robust as far as holing pistons go. Being too lean might get you a soft seize, but I don't recall ever burning a hole in a piston.
I'd suspect you'll need to bump them up another size.
And that engine design is pretty robust as far as holing pistons go. Being too lean might get you a soft seize, but I don't recall ever burning a hole in a piston.
Oh HELL ya !!!!!!
Very nice to the see the RDs. Brings back lots of memories.
I had the 1975 RD250B and loved it to pieces, so smooth...
Easy to tune and when correctly done would just zip clean to redline without any hesitation. My only gripe was all the smoke above 5000 rpm. My mate's Suzuki Titan 500 and GT250 did not smoke like the RDs. When I moved to the XS1B I was a little concerned about the jump to higher power, but I never noticed anything of concern switching between the two except the RD was snappier. Once I was low on gas out in the countryside and could only get SUPER instead of REGULAR. After about 5 miles the motor started banging a bit then seemed to settle down. I rode the 80 miles home then took the heads off. I was able to lift the head of the left piston clean off. To this day I still do not understand what the change to SUPER had to do with the piston failure...
Anyone have an explanation????
I had the 1975 RD250B and loved it to pieces, so smooth...
Easy to tune and when correctly done would just zip clean to redline without any hesitation. My only gripe was all the smoke above 5000 rpm. My mate's Suzuki Titan 500 and GT250 did not smoke like the RDs. When I moved to the XS1B I was a little concerned about the jump to higher power, but I never noticed anything of concern switching between the two except the RD was snappier. Once I was low on gas out in the countryside and could only get SUPER instead of REGULAR. After about 5 miles the motor started banging a bit then seemed to settle down. I rode the 80 miles home then took the heads off. I was able to lift the head of the left piston clean off. To this day I still do not understand what the change to SUPER had to do with the piston failure...Anyone have an explanation????
Not sure ,but different fuels have different Combustion Characteristics
SAAB installed a knock sensor on the block and adjusted the ignition Partly that signal.
What does the knocking sensor do?
Knock Sensor | Cars.com
The engine's knock sensor (or sensors) detects preignition and detonation, potentially damaging forms of abnormal combustion. Though full-blown knocking and pinging are audible to the human ear, the knock sensor detects imperceptible levels.
Petrol is not always perfect there can be chemicals that are cheaper than gasoline and contain water from the filling station tanks.
The automated filling stations with no staff had poor reputation. Back then
These days ethanol that sometimes forces owners to readjust ignition timing.
A 2 stroke is what I hear more sensitive and Kawasaki Mach 3 had the reputation overheating the middle cylinder
SAAB installed a knock sensor on the block and adjusted the ignition Partly that signal.
What does the knocking sensor do?
Knock Sensor | Cars.com
The engine's knock sensor (or sensors) detects preignition and detonation, potentially damaging forms of abnormal combustion. Though full-blown knocking and pinging are audible to the human ear, the knock sensor detects imperceptible levels.
Petrol is not always perfect there can be chemicals that are cheaper than gasoline and contain water from the filling station tanks.
The automated filling stations with no staff had poor reputation. Back then
These days ethanol that sometimes forces owners to readjust ignition timing.
A 2 stroke is what I hear more sensitive and Kawasaki Mach 3 had the reputation overheating the middle cylinder
Well, got my leak down/pressure test kit built and sure as 
smells brown...I found an air leak 
.
It was at the base gasket right where the two cylinders Siamese together on the front of crankcase.
Sitting all those years weren't kind to the lil air-cooled engine I reckon? Already pulled it apart, pistons appear to have gotten hot past the rings.
However, there's absolutely no scoring, no ring ridges, still good cross hatch in bores...
Question is now...do I check ring end gaps, put it back together with new circlips & gaskets and continue my leak down test to check crank seals?
Or, do I go down that slippery slope....pull the engine, split the cases, put all new seals in it, etc...
I know how I am, the aircraft maintainer in me has a hard time stopping...its always "Well, since Im in here I may as well..." Then it takes forever to finish!
Throwing top end back on will only take a short while, versus the full monty...
smells brown...I found an air leak . It was at the base gasket right where the two cylinders Siamese together on the front of crankcase.
Sitting all those years weren't kind to the lil air-cooled engine I reckon? Already pulled it apart, pistons appear to have gotten hot past the rings.
However, there's absolutely no scoring, no ring ridges, still good cross hatch in bores...
Question is now...do I check ring end gaps, put it back together with new circlips & gaskets and continue my leak down test to check crank seals?
Or, do I go down that slippery slope....pull the engine, split the cases, put all new seals in it, etc...
I know how I am, the aircraft maintainer in me has a hard time stopping...its always "Well, since Im in here I may as well..." Then it takes forever to finish!
Throwing top end back on will only take a short while, versus the full monty...
That's not too bad considerin' it's a 2 stroke.
Iirc, crank end seals can be replaced without splitting the cases. The center is a labyrinth seal. Doesn't need changing except at crank rebuild time.
Reachin' way back... but both R5's and RD's used the same type of ribbed seal. Impossible to install with the halves together. New generation (replacement) seals had a smaller rib. Big enough to hold in the groove, but small enough to be pushed in without splitting the cases.
As an aside... a brand new razor blade will shave just enough from the rib, it'll press in. Don't ask how I know that...
Course, I might be thinking of a different engine. They all run together over the years...
As an aside... a brand new razor blade will shave just enough from the rib, it'll press in. Don't ask how I know that...
Course, I might be thinking of a different engine.
They all run together over the years...Odometer ?
Assuming we are talking the one with intact saddle The Machine does not look as seen much use.
No experience of 2 strokes or these
But if Low mileage I would try to go for a smaller job now. If possible Things can go wrong splitting and taking it apart.
For me anyways
Assuming we are talking the one with intact saddle The Machine does not look as seen much use.
No experience of 2 strokes or these
But if Low mileage I would try to go for a smaller job now. If possible Things can go wrong splitting and taking it apart.
For me anyways
Kind of how Im leaning, yes....particularly if Jim thinks those pistons dont look too far cooked?
It is indeed the 1400 mile bike and theres zero scoring anywhere.
Forgot about the low (1400) mileage. That's a bit much for that few miles. Still, I wouldn't worry about it. Jus' shootin' from the hip... maybe the oil pump is turned up a little too much?
Were it me... I'd clean the pistons and jugs and put it back together.
And maybe do a little research on replacing crank seals without splittin' the case. I'm almost certain we used to do it that way.
For those wanting to see a leak down test - The symptoms of a leaking seal are discussed from 1:30 to 3:00. Following this is discussion as to where to get the required equipment. The actual testing starts at 8 minutes and is nicely explained.
I've been a subscriber to his channel for quite some time. He's a little unorthodox at times but he has some great content.
I have a question. I'm not at all well versed on multi-cylinder 2 strokes. I have always thought they all had a "center seal" in the crank to keep the cylinders isolated from each other. I know the Kawasaki motors in Arctic Cat snowmobiles did, if it leaked the engines ran very erratic.
He put air in the left cylinder and got pressure in both right and left. So the air was getting from the left side to the right somehow. I'm a little confused. No seal between the Yamaha cylinders?
He put air in the left cylinder and got pressure in both right and left. So the air was getting from the left side to the right somehow. I'm a little confused. No seal between the Yamaha cylinders?
Yamaha twins use what's called a labyrinth seal between the cylinders. It's made from aluminum (iirc
) so there's almost no wear unless you get a wobble in the crank (bend it).Labyrinth seals aren't perfect, they'll leak a tad... but they're good enough.
Yes, air went from one side to the other... but with both sides capped, we should hold air indefinitely provided nothing else leaks.
So yeah, no way to really check the center seal, but as I said... really no need to, they'll last forever.
