RD 350 transfer port cleanup

[Dvsrd]

Gents,
I have a spare set of stock RD 350 cylinders, still at stock bore, that I am considering having bored to +.25 or +.50 mm, as well as converting them to RD400 head gaskets and fitting dowels to locate heads.
Is it worthwhile having a local 2 stroke shop clean up the transfer ports first. Just removing any steps and casting flaws in the upper part of the transfer ducts and the ports. And maybe cutting the boost ports a bit deeper as well. No plans for more exhaust port duration, however.

[1976RD400C]

If you have an air compressor you could buy a die grinder at Harbor Freight and clean up the ports yourself.

[m in sc]

if you local shop has a porting tool, then yeah its not  bad idea, the roofs of those ports shaped and cleaned up can def help.

[Dvsrd]

I do have straight die grinder, a Dremel etc, but no right angle handpiece. And since those are pretty expensive, I am looking at having this done by a somewhat local shop. I can easily deal with intake and exhaust ports myself, but do not intend to change timing, maybe just improve the exhaust port finish to slow down carbon buildup.

[automan]

Sand blast

[sav0r (CL MotoTech)]

Reducing and removing the ledge is basically the first thing you do. Matching the sleeve at the divider is common. I see a lot of knife edged cylinders there. Knife edging is easy but it's old school. Nice rounded and blended ports are preferred. Then clean up and set port timing.

[IR8D8R]

I picked up a Chinese Vevor Foredom knockoff flex-shaft grinder and a right angle attachment on Amazon for ~$150. That's really the setup you want for port grinding cylinders. Dremels don't have enough power. I've used air die grinders on cast iron ports and they're so noisy and really require a big compressor tank and 2 cylinder compressor head. My 20 Gallon 5hp Sears compressor won't keep up so I have 2 compressors feeding the same air line. Super noisy with all that running in my shop.

A real Foredom is almost $300 without the right angle handpiece which is almost as much as the tool. I'm pretty happy with the Vevor even though I'm not fond of sending my money to China. My only complaint is that the foot switch is not variable speed. Just on/off.

IR8D8R

[1976RD400C]

John Ritter worked some magic on my 400 cylinders. RZ size reeds.

[RDnuTZ]

RE: Vevor, I read a recent article in business pages Vevor will be opening multiple brick and mortar stores in US this year to compete with the likes of Home Depot, Lowes, Harbor Freight, Tractor Supply all under 1 roof. I bought a Digital readout Torque wrench off eBay that looks to be good quality and currently waiting for delivery of their branded air hose. The website that tracks your purchase looks really sophisticated too like all set for the big launch...

[RDnuTZ]

John Ritter worked some magic on my 400 cylinders. RZ size reeds.

very nice 

[SmokeAddicted]

Gents,
I have a spare set of stock RD 350 cylinders, still at stock bore, that I am considering having bored to +.25 or +.50 mm, as well as converting them to RD400 head gaskets and fitting dowels to locate heads.
Is it worthwhile having a local 2 stroke shop clean up the transfer ports first. Just removing any steps and casting flaws in the upper part of the transfer ducts and the ports. And maybe cutting the boost ports a bit deeper as well. No plans for more exhaust port duration, however.

Gents,
I have a spare set of stock RD 350 cylinders, still at stock bore, that I am considering having bored to +.25 or +.50 mm, as well as converting them to RD400 head gaskets and fitting dowels to locate heads.
Is it worthwhile having a local 2 stroke shop clean up the transfer ports first. Just removing any steps and casting flaws in the upper part of the transfer ducts and the ports. And maybe cutting the boost ports a bit deeper as well. No plans for more exhaust port duration, however.

Promise not to hi-jack the thread here. I'm 6 months into owning an RD and cleaning up the aesthetics, and I'm finally starting to think a little more about the engine itself.

I understand the concept of over-boring and port cleanup. Can someone elaborate on the RD400 head gasket and "dowels" to locate the heads? Are we simply discussing altering squish/compression? Going slightly more towards a race tune? Much appreciate y'all's insight.

[m in sc]

doweling a cyl head and cleaning up squish, really, is an efficiency thing. centering the dome makes for a better combustion chamber as does tightening the squish. 

on my tzr, with everything in the motor stock, the head was cut to .8-.9mm squish.  what this does is actually center the mixture for an optimal burn, and allows it to run cooler. to the point, the harder you flog it the cooler it runs due to it being so efficient.  its weird watching the temp gauge drop some at long sustained high rpm runs. but it does it. this of course helps when adding performance mods. you can do one e out the other. my t500 w the billet heads has dead stock porting as well, but an actual squish band and o ring head and centering made a big difference alone. Chuck q used to recommend centering even stock heads on 400 builds, and changing over to 400 type head gaskets in 350 builds & correcting the squish.

[SmokeAddicted]

Wow. Reducing squish makes sense to me from the standpoint of raising compression, but I NEVER would have considered that a stock head isn't truly centered. It all makes sense though. Talk about some delicate machining work with a little wizardry!! I've tried reading 2T Tuners Handbook, but I feel like you need an engineering degree to understand half of what's being said. If you have any other resources, please point me in that direction! Thanks, Marc. Very very cool stuff.

[85RZwade]

The technology is a little outdated, but A. Graham Bell's tuning book is excellent and an easier read.

[m in sc]

I have engineering degrees.that stuff gets very boring to read even to me. 

compression is one thing, but IMHO not nearly as important as to where the mixture is located/directed when burned. hence  the shaping of the chambers etc. its all VERY different as to how a 4 stroke works overall.  best way to view it for comparison,  to me, is compression is dynamic on a 2t, the faster you rev it, the more it effectively makes. hence why its good to retard the timing higher in the rpm range