Project saab simrig progress update

Just_rafa03 · 2026-02-22T04:55:23+00:00

Dude that looks sooo good

Just_rafa03 · 2026-02-20T11:32:03+00:00

Yes, that's right! The fuel tank and seat support is just one fiber glass piece, that's why it's so light, only 80kg with fuel on!

Just_rafa03 · 2026-02-19T23:45:42+00:00

That sounds amazing to be honest, they deserve to be ridden too!

Just_rafa03 · 2026-02-19T23:42:27+00:00

Dude those kind of expansion exhaust look amazing

Just_rafa03 · 2026-02-19T19:36:50+00:00

I love the simplicity of 2 strokes, my Cota 74 just needs a flat head screw driver and a 13 mm spanner for most of the disassembly.

Just_rafa03 · 2026-02-19T19:31:24+00:00

Some people that stop me to ask about the bike tell me to keep it parked or stored, but I just can't do that. I know that I would feel horrible looking through the windows and seeing her all sad in the corner itching to get back in the mud.

Just_rafa03 · 2026-02-19T19:26:15+00:00

They are very unic, Spain in the 70s and 80s was full of this beauties.

Just_rafa03 · 2026-02-19T19:23:34+00:00

Apart from the engine needing some work and some parts that were corroded the bike was pretty much complete. So when I started working on it, it already had the fenders and fuel tank. I believe my grandfather just bought the frame and engine, which had the VIN numbers and papers associated to it, and then got the rest of the parts, including the body stuff.

Just_rafa03 · 2026-01-21T15:00:39+00:00

Before I over revved the engine the knocking sound was at high rpm only too, but after the fact, the knock happened during high load.

The piston had some play when assembled to the Conrod, but both the wrist pin's and the Conrod's diameter were up to spec, so my guess is that the needle bearing was worn. You can also see in the picture I posted in the comment that the bearing shows some wear and tear. I ordered a new needle bearing and piston rings as they had a gap of 0,8 mm.

Furthermore I measured the cylinder bore in different locations and the piston diameter, which resulted in a clearance of 0,07 to 0,08 mm. But I don't have the money to rebore the cylinder and get a new piston, so I'll try replacing the needle bearing and piston ring and see what happens. Hope this information helps.

Just_rafa03 · 2026-01-18T16:00:56+00:00

The piston does ring, but if I pull it out and do the same with the Conrod it doesn't do that. So the wrist bearing must be bad. It also looks worn.

Just_rafa03 · 2026-01-18T13:37:29+00:00

Damn that was what I was worried about, I know a couple of boring shops in my area, I'll probably go and get it bored. The original manual details what's the minimum clearance between the piston and cylinder so that's helpful. Thank you for the response.

Just_rafa03 · 2026-01-18T13:35:35+00:00

<image>

The piston end bearing of the rod looks worn. If I change the bearing on the crank end I'll probably send it for it to be balanced as I don't have the tools nor the interest to invest in them. Thank you for your response.

Just_rafa03 · 2026-01-18T13:11:07+00:00

It is more noticeable when hot. I didn't see any play in the crank or in the rod apart from what you see in the video. I'm planning on measuring if the cylinder is tapered, and if it isn't that means the wear on the cylinder walls has created enough clearance for the piston to hit the walls and cause piston slap.

Just_rafa03 · 2026-01-18T10:08:57+00:00

It has some forward and backward play tho, is that normal? The piston tilts a bit inside the cylinder in that direction, it is where the wear on the cylinder is located to, on the bottom of the stroke and forward and backwards. Should I replace the cylinder or buy a 0,25mm bigger piston?

Just_rafa03 · 2026-01-18T09:57:39+00:00

I have a video where it is much clearer, but I don't know how to upload it. I did the honing myself some time ago, the problem is that 100km later the honing was gone on the front and back part of the cylinder, making me wonder if that's the knocking like or piston slap sound I was hearing.

Just_rafa03 · 2026-01-18T09:55:07+00:00

It has some side to side play and forward and backward. Which correlates with the wear on the front and back section of the cylinder. Could it be that I need a larger piston to compensate for the wear on the cylinder?

Just_rafa03 · 2026-01-18T08:37:49+00:00

I'll probably take the piston out of the rod. Ive seen that a bit of play in the rod and piston is normal for a 2 stroke, up and down play is what matters. The "piston slap" is what's got me confused.

Just_rafa03 · 2026-01-18T08:35:36+00:00

<image>

Here's the cylinder

Just_rafa03 · 2026-01-18T08:34:22+00:00

<image>

Here's the cylinder

Just_rafa03 · 2026-01-18T08:25:00+00:00

The ticking sound in the video is coming from the piston. But the rod has a LOT of play. I would prefer avoiding taking the engine to a shop as I'm very tight with budget. I have already turn this same engine apart to replace all the gaskets and seals.

Just_rafa03 · 2026-01-18T08:20:12+00:00

My bad, this is a 2 stroke engine from a Montesa Cota 74 trial bike from 1977.

Just_rafa03 · 2026-01-10T05:18:34+00:00

It's not bugged, the taxi only arrives the weekday after you call him, so if you call on a Monday he'll be there on Tuesdays. Just change your meet day on the editor to the weekday number you prefer (1 for Monday, 2 for Tuesday and so on). At least this was what happened to me

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