honning a robins 350cc mci block question

uwantsumofthis

So I tore my robins 350cc mci block down. I measured the cylinder walls with the telescoping gauge and digital caliper. I'm getting 2.6385" or 67.019mm. In my rebuild manual this is the furthest limit for factory pistons. So 2 my understanding I have to go .25mm over size pistons. Now I have 3 questions about honing.

First one is, what size should I hone the bore 2. Should I go to the factory new engine spec, and just add .25mm? Or does any body suggest any different number bore?

Second, in the manual it tells me to use a 2.5" 240 grit flex hone ball 2 hone the cylinder. I tried looking for the ezgo part number online and no luck. I did find one on Ebay for 33.50$ shipped. Now do I use a stone cylinder honing tool to a certain bore, then use the 2.5 flex ball to finish out the hone. Or do I just use the 2.5 flex ball until desired bore?

Third and final question, what liquid or solvent to use for honing? Manual has a ezgo part number for a solvent but no luck searching for it.

Any advise, I know we have some dame fine machinist in here!!!!

BGW

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Diceman1530

Use stones to hone to size,you will need coarse ones to get close then finer one to finish. The ball hone will not keep the bore straight. You will have to keep checking the bore to make sure you don't have big and small areas.
You will need the piston first,measure it then add the piston to wall clearance desired. Good luck take your time and keep checking the bore size.
Measure top,bottom and center.

Diceman1530

http://www.goodson.com Has what you need
Honing oil and hones

uwantsumofthis

Thanks a lot dice!i just looked on the site and was checking out the stone hones.brings me to another question,im assuming to buy the cast iron ones because I think the cylinders R cast iron.Correct me if I'm wrong. I do know lower the grit the more course it gets, but what grits would u recommend for course, and fine grit?

uwantsumofthis

Looked at the prices on that site and said way to much for my buget. I have a stone hone from autozone, but didn't know the grit. So I checked the autozone site, and they sell replacement stones with different grits. For course they sell a 100 grit. For medium they sell a 220 grit. For fine they sell a 400 grit. 11.99 each set. As for the honning oil, I found sum on ebay for 20$. I was thinking of buying expensive tools when I bought all the measuring tools, but buget wise had to go the harbor freight way.

I haven't ordered Pistons yet, but will somtime this week. If they r to spec like in the repair manual then the 67.25mm will work just fine. Factory bore is 67mm, .25os piston bore is the 67.25, so I guess if I have to do this again the .5os piston bore is 67.5mm. I will not do any boring till I have Pistons in hand.

Thanks again dice!!!Dice Rules!!!

uwantsumofthis

Please do not use the cheap autozone or haborfreight honing tool. I just used it with the different stones they sell and ruined my crankcase. The hone followed the shape of the cylinder and only removed to much from the top and bottom of cylinder, and not enough from the center.I have another engine I needed the heads off of so I will using them. I guess I can sling the crankshaft, and other parts I don't use on ebay. The lesson here is don't use cheap honing tools for boring.

JG4660

I'd take it to a machine shop when you get the pistons...for what your gonna spend on tools you'll just about pay for a professional to do it.

MarineGrunt

I agree with JG and Uwant.

Honing and boring are two different things. Honing is used to get the tool marks out after boring if need be and to finish the walls. Boring will give you a good straight hole. Not saying you can't use a hone to bore but it doesn't take much to screw it up. The spring loaded hones won't correct bore errors. If the bore is slightly oval the springs are going to continue to form to that oval. Honing is more to clean up surface imperfections. I've used a ball hone to clean up score marks and such but never to actually bore. It doesn't take much of an imperfection to start losing compression.

If you take it to a machine shop it'll cost you less than $50 per cylinder so you're under $100 for both. At least that's what it costs in my area. You'll then know you have a perfectly true bore. If you go that route be sure to take the new piston and rings with you. Hand them the head and pistons and you're done.

If you're adamant about trying it yourself get a rigid hone.

sccowboy

If it were me, and unless you just want the experience, I would print the spec page out of the book and take the block and specs to a reputable machine shop. They will do it right and you won't have to deal with figuring all of it out. If you are sure you need the .50 pistons then go ahead and get them to take to the shop with you. Last one I did that way came out perfect, and I wasn't out much cash.

uwantsumofthis

I just want the experience! Lesson Learned! Unless u have some g's to spend on a BORING machine, leave the boring up 2 the machinist! Even some of them high dollar portable hones follow the cylinder insted of reshaping it.