Ports toast??

Joshua · February 25, 2019, 07:39:24 AM

Thankful the site is back up. Thanks for all the hard work everyone.

Can I get some feedback on my exhaust ports. They look like someone before me did a bad job, just wanting to know if they look salvageable. Almost have my roller together and am planning ahead for the motor. Thanks for any feedback. Was hoping to send off the motor to chuck as I'm not to far from him, but it's taking a bit longer for this project to get rolling.

thatguy · February 25, 2019, 03:38:42 PM

Before writing them off or spending time fixing I'd check the port timing of the cylinder. They don't look too awful but that's just looking at a photo. See if they'd be suitable for your intended use.

Eric P · February 25, 2019, 04:56:21 PM

It's very difficult to tell from pictures like that.

Things to check:
- Put the pistons at the bottom of the stroke and make sure that the crown of the piston is level with the bottom of the exhaust port.
- Use a degree wheel to measure the port timings and see what RPM you're making power.
- Measure the the exhaust port width. It should be no more than 67% of the bore diameter. You will need to remove the cylinder and make a port map to verify this.
- While you're in there, make sure all of the ports are adequately chamfered where they meet the cylinder so your rings don't snag.

From what I can see, it doesn't look overly terrible. I've seen some genuinely bad porting that still ran fine. As long as the above items check out, I'd probably run them. Maybe clean them up a bit first if you're worried about it.

Any idea what the intake ports look like?

Joshua · February 25, 2019, 09:59:54 PM

Thanks for the responses. I'm new to rebuilding the rd's so I'm learning. I'll most likely send the porting work out as I don't have the tooling to gauge both ports properly. I ported my miata head with great results, but I started with a stock head. I've got a lot of research to do before I move on, but wanted to know if the head was worth moving forward with. Intake ports are below. Thanks for the feedback. I'll look into what you guys mentioned.

Hardy · February 25, 2019, 10:50:23 PM

I also have a set of barrels like this, where the liner has been mowed down to "improve" the port.

I've not fitted them as they are in a box of spare parts. I am interested what effect having the port lower than the piston at BDC will cause?

Joshua · February 26, 2019, 07:58:20 AM

I'll check TDC and BDC when I get home tonight. Hopefully they are workable for a fun hooligan bike. Lol.

Thanks, things are making more sense.

teazer · February 26, 2019, 05:27:47 PM

it doesn't matter much if the exhaust port floor is below the top of the piston because there is very little flow down there.

Joshua · February 26, 2019, 08:12:34 PM

Yeah, I'm not liking what I'm seeing. Exhaust ports. Left side looks to me like it's cracked and barely hanging on. Could be from an exposed weak spot that the porting job did, but I'm not happy about how this looks.

Hardy · February 27, 2019, 12:39:00 AM

Crack or low point in the casting, that wasn't taken away when the port was cleaned up?

Joshua · February 27, 2019, 07:58:16 AM

This really is my first look into this motor, the bike is in pieces, so I was looking into cleaning and rebuilding the motor. Before I spend the time to clean up the case, I wanted to make sure it's workable.

teazer · February 27, 2019, 06:28:38 PM

What are the barrels from? I thought that all RDs had a recess for the exhaust gasket. Those look like someone welded in an aluminum ring to work with an aftermarket exhaust system. That's exactly where that "crack" appears to be. I would not worry about that. Measure your ports and compare to stock and check that the exhaust ports are not larger than the exhaust pipe mounting stubs.

Stock RD350 ports are all pretty horrible and the transfers suck. Even the cheap aftermarket Chinese barrels are better than stock in the main transfers. I am yet to see a production casting where the iron/aluminum interface is perfect and it take quite a lot of work to make them look presentable and work well. Ask Chuck. He's done lots of them and knows how much work it takes to get them right.

SUPERTUNE · March 07, 2019, 09:42:02 AM

Sorry guys I've been missing around here...Vintage AHMRA races started 2 weeks ago and on the road to Nola for the 2nd race weekend this early am.
Are these Daytona cylinders?
Send these pics to my email and I'll be able to see them better on my desktop computer. Looking and posting here with a cell is not very good for me.
Chuck

EE · March 14, 2019, 08:47:14 PM

Yeah their Daytona cylinders. Guys don't like to hear it but the outlets on RDs are already a little too big, they start at a small ex port (at the liner)and "trumpet" to the 37ish mm outlet, once you start opening up the ex port (at the liner) for racing the mismatch gets less so that's good but that area about a 1/4 inch back is almost always even bigger (on aircooled RD's) than the outlet as that's where they add the flange section to the casting, if you take out all the material to make the port look "pretty" there you end up with an even bigger outlet and hp actually drops or if you try to keep the outlet at 37 and work out the low spots you end up with dips and larger sectional area spots in the port that hurt performance once again. sure the guy could have done a better finish on the ports (though polishing is not a real benefit) but he was smart not to just hog the port to the id of that low spot just to them look pretty..

SUPERTUNE · March 16, 2019, 09:16:01 AM

And to add that... the Daytona exhaust port is a better design, has no compression bleed hole, smaller runners is better too, except the emission low port duration. Bolt pattern and angle is different on the Daytona's and require modifying pipe fitment to 1A1 model RD's.
Chuck

EE · March 17, 2019, 08:51:38 AM

Yeah the Daytonas had a little better ex port floor shape, they still had a valley in the ex port floors but it wasn't as bad and started to have some "hump" to it, a good shape for ex port floors BUT because of the ex valves they jogged the ex ports toward the center of the engine not horribly but if they'd just kept them straight! The other real benefit was in the better transfers. Non US 2R9s didn't have the jog in the ex but did have the small compression bleed port but also had the better transfers. The Daytonas also had their intakes smaller and lower than both the US and 2R9 cylinders. So all three versions of the 4oo cylinders had their good and bad points.. For racing I plug and weld the ex compression bleed ports as I'm sure Chuck does too. Ed

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Ports toast??