1977 Suzuki A50 build is complete! (Ha!)

[Raizer]

Was still tapping, so I pulled the top end off.
Looks like I should have paid more attention, when I built the engine I used a projected tip plug which looks like it has been getting slightly touchy-feely with the piston lol




A new standard tip plug is much better!



Also it felt a bit lean at WOT and I thought it started to semi seize a couple times, found a few rough bits on the piston where it likely had been grabbing a bit, didn't take much to polish them out though.
Up-jetted a bit

And in the process I realized it has all the 4 stroke AN atomizer parts in it, so I think I am going to upgrade to a new PHBG with AN262, 40 slide, W7 needle, bowl with cap and the idle and mix on the opposite side to this one.



Think the new filter is a bit small?

[tsimi]

Best mod on this bike is the key as hose guide.  

[Raizer]

Sept 22, 2020 23:38:07 GMT -5 tsimi said:

Best mod on this bike is the key as hose guide.  

It's the key to speed!!

Here's another little detail that I neglected to post before:

Little bit of fireball to keep warm with while waiting for any 4 strokes to catch up on group rides

[Raizer]

Still tapping with.7 copper gasket, was good for maybe a minute then got noisy again.

Pulled the head and spotted what looked like faint witness marks on the squish band

*I had polished it before it went back on last

So I made a .9 alloy gasket

Same deal, fired it up and it sounded perfect, nothing but sweet sweet 2 stroke music!!   
For maybe a minute at most

*It died as I'd turned the fuel off to empty the carb*

Still thinking that the piston was hitting the head as things got warm and expanded I quickly pulled the plug and measured squish while the engine was hot.

Got .8mm at 3 different points around the piston, so it's not hitting at all.

So now I'm slightly at a loss, but am thinking it may be detonation from too much ignition advance combined with high compression.

[Steve B]

Raizer, You are an amazing creator. Great job with the thread, I love how many pictures you include it's like a Wimmelbook you did such great photography. Keep up the hard work as I will be following you closely.

[Raizer]

Checked the timing, was about 23°, played with it between 22° to 28° BTDC, no change to the noise at all.



Have left it set to 24°, should probably back it off to 26° or so as I confirmed the CDI does in fact have an advance curve built in.
I'm impressed by the ToolPRO timing light so far, 99% sure they are a re-badged Innova 5568 *Halve the RPM numbers, it doesn't go below 2 cylinder in 2t mode*



So now I'm back at square one with the noise, screwdriver stethoscope says it is in the top end but I'm running out of ideas!

Edit: after watching a fair few videos of dirt bikes with failing big end bearings I'm fairly confident that it's what's wrong with mine, I recently measured up the side play of the rod and it was well within spec but that doesn't rule out damaged needle rollers in the bearing, either from rust or crud getting into them while sitting, or even abuse with crap 2t oil etc.

Also it had felt like it was seizing a couple more times but without leaving a single new mark on the piston, which would also line up with big end failure.
Guess it would also explain the mystery "clutch noise" the old owner of the donor engine was hearing.

So now I'm attempting to either track down all the genuine Suzuki parts needed (have already got the bearing and can get a rod and pin from Japan, but the thrust washers are apparently harder to find), or go with an after market rod kit, not really looking forward to striping it yet again especially now that riding weather has arrived!!

[Raizer]

Guess I'd better tear it apart again then.

[Raizer]

After a real mega struggle pulling the carb off/out of it's o-ring retained hole, I dropped the engine outagain, then stripped the engine again.

One thing that had been bugging me since I first built it was the crank web blocking 3-4mm of the intake port



Figure while it's apart yet again I might as well take the opportunity to do something about it!




Doesn't really look like much was taken off, but hey it should breath better so that's got to be a good thing!
Now to package up the crank and send it off to get built.

Also I found a replacement for the massive Uni filter

[nikola11]

Very nice build
That machining of the crank web looks like it could help the air flow but I was wondering if that will increase your crankcase volume which could make crankcase preasures drop while the engine is at bdc and the transfers are open?

[Raizer]

Oct 16, 2020 11:52:21 GMT -5 nikola11 said:

Very nice build
That machining of the crank web looks like it could help the air flow but I was wondering if that will increase your crankcase volume which could make crankcase preasures drop while the engine is at bdc and the transfers are open?

Yeah it will increase the crankcase volume for sure, that's why we took only the off absolute minimum amount needed to open the port.
It's a slight trade off, but after talking to the old owner of the intake it's very much worth doing, his crank was machined further than mine and still made good gains

[Raizer]

Crank got sent away to be rebuilt this morning, should have it back later this week.

My new PHBG finally came in from Treatland as well as a few bits from Pedparts and I've finally got the proper tools for splitting cases and pulling bearings.

[Steve B]

This is gonna be good can't wait.

[aeroxbud]

Nice. The proper tools do make it easier when rebuilding stuff.

[Raizer]

Oct 19, 2020 4:36:12 GMT -5 aeroxbud said:

Nice. The proper tools do make it easier when rebuilding stuff.

The definition of proper tools can vary depending on who you ask though
This is from the Suzuki FSM in regards to fitting the crank

Things have changed a bit since the 70s haha!

[aeroxbud]

Even now I have seen some places advising just to pull the crank into the cases. No heat involved.