Os max rz engine help

[zeus r/c]

So i got this os max rz in a trade a month ago has very little compression so I'm thinking new bearings piston and sleeve i have not tore into yet but i put it on my bump start new plug clean lines factory carb setting and wont fire however i can spin the crank with 1 finger hence why i say very little compression here my thing I've been looking and I've seen several things but would really like some more in for on what it actaully is before i start buying stuff and maybe just maybe someone here has some part numbers or other option set ups for this engine i know its an older engine I'm just not to familiar with os max or os for that matter just been told its a really good engine any info or part number would help alot thanks guys keep burning nitro

 

[ohsnap]

Hey Zeus,
Yeah, if you easily spin the crankshaft with the glow plug in place, it needs a new piston & cylinder - or at least a re-pinch.
Since I've never dealt with a re-pinch, I can offer no help when it comes to this process.
Like you are thinking, I would replace the bearings at this point.
You may have thought it but did not mention it.
Conrod too.

I always liked those OS engines - buddy still runs one from time to time.
Yours look like this?

OS has a great website which contains the historical engine information that you are looking for.
Find your engine and you'll find the manual and part numbers.

OS discontinued engines list and info:
https://www.os-engines.co.jp/english/line_up/stop_list.htm

The bearings, connecting rod, piston pin, and piston pin retainer are relatively easy to find and for the most part, reasonably priced.

Now the bad news.
Unless you're jonesing to run a vintage engine, you are probably better off buying a current one.
The piston and cylinder are difficult to find and expensive when you find one.
You will probably end up spending over $300 for the parts, and unless you have a bearing puller and press, add more for tools.
The Hudy Ultimate Engine tool kit itself runs over $100.

I found each of these today for approximately $300.

 

[zeus r/c]

Yes sir mine looks exactly like that and I'm at the point either rebuild it or sell it as it is

 

[ohsnap]

I've have never dealt with this company - but I found what I expected to be your hardest part to find at a lower price than I expected...
I paid a lot more for an OS MAX-21VZ-B piston and cylinder set a few years back.

Hobby wholesale
(They appear to be a legit Canadian company - but I just did a quick check - you may want to look into them a little more before ordering)
https://hobbywholesale.com/radio-control/gas-nitro-engines/engine-parts/parts-accessories.html?p=2
If their pages have changed around and it doesn't show up - you can search on the full part number (OSM23703040)