engine blowby

[mike1969]

First off, I probably screwed up. Don't be afraid to tell me if I did. Just trying to figure out where to go from here. Do I have to tear the engine apart and start over or will it possibly cure itself?

Finally got my 305 Dream on the road after 6 years of getting it roadworthy.

My engine was badly seized so I purchased low mile cylinders. I didn't do any measurements on the cylinders ( big mistake)

Found nos std. pistons on ebay for $10 and got new std. rings for $11. I figured i'd give it a shot.

After getting the engine in the bike I got it running and tuned. It starts instantly with electirc starter and first kick. It has 125 lb. compression when cold.

The problem: I was getting a lot of blowby from the engine breather and leaking from all of the seals.

A friend who restores old cars recommended the valves could be out of adjustment and causing too much combustion pressure in the cyls. The valves were out of adjustment. After adjusting the valves it ran much better and the oil quit coming out of the seals but still oil coming from the engine vent.
I put the hose in a small plastic bottle to catch the oil. After about 75 miles I got about 2 ounces of oil.
It runs fantastic has plenty of power and doesn't smoke.

Could there be any problems other than ring problems (maybe badly installed) or excessive cylinder wear?

[Snakeoil]

Hard to say with no measurements taken during the assembly process. You should have at the very least checked your ring end gaps in each cylinder. Engines will run with excessive end gap, but be down on compression and have a tendency to blow by thru the excessive end gap.

There is an old axiom a guy I worked with for years always used in cases like this. He even had polo shirts made with this on the sleeve for young engineers to wear on job sites.

"To measure is to know."

You can never have enough information. You can either live with your problem or pull off the top end and see what is not to spec. Could be you got a bad set of rings. But chances are, the jugs have been bored oversize. Was there a ridge at the top of the jugs from wear? Was there any cross-hatch pattern from honing? Did you hone before you assembled the engine?
Good luck,
Rob

[mike1969]

Snakeoil,

Thanks for the input.

I had zero experience at rebuilding engines when I dove into this.

I didn't find out about this forum until 2 years later to ask for technical info.


The cylinders had no sign of wear but I really don't remember about the ridge.

Looks like a teardown is in order. I'll probably pull it back apart this fall.

I also have another set of cylinders I may be able to use. Anyone know what's the max cylinder size to use std. pistons?

If the cylinders are within the size limit to use standard pistons
what is the maximum ring size that I can go with. I've seen them on ebay that are .25mm over.

I appreciate any help given

[OldStan]

.25mm over rings go with .25 mm over pistons. Standard pistons are only used with standard rings. The book I have says the wear limit is 60.10mm (2.366".) I'm sure there are probably differing opinions on what you can live with.

[mike1969]

Thanks Stan,
I didn't realize the pistons and cylinders clearances were that critical. No wonder i'm having problems! I'm amazed it runs as well it does.

I'll go with that measurement when I have my cylinders checked out.

[Snakeoil]

I posted links in the literature section for parts and service manuals that are available on-line for the bike. You can download them and print them out.

I would suggest that you get yourself a "engine basics" book from a local book store or on-line. You need to establish some baseline knowledge. We were all newbies to engines at one time so I'm sure others will chime in that some basics regarding how engines are built and/or rebuilt would serve you well.

My guess is you have no "feel" for what is required and that can bite you. Always assume that there is a right and wrong way to do anything regarding an engine and seek out the correct way, either thru a manual or asking questions. Keep in mind that when you ask a question, you will only get the answer to that question and more info might be required to complete the task. Not talking down to you because like I said, we have all been there at one time. Be patient and read up on the basics. It will make it that much more fun as you dig back into the engine.

regards,
Rob

[mike1969]

Thanks Rob, I appreciate the advice. Ill look up that info.

Not looking forward to tearing back into the engine though!
But it should be a lot easier with more knowledge.

Mike