Honda Z600 Rebuild Nits and Lessons

Entry posted by scrottie February 9, 2015

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Here are some lesson I learned when purchasing and then rebuilding a Honda Z600 [see footnote 1 if you're not familiar]:

The engine is really only good for about 75,000 miles before it needs a rebuild. Air cooled engines run hot, and that means lubrication is less effective. It also has some design flaws, detailed below. Most N and Z600s on the market are at or near this [footnote 2].

Between the crankcase and the cylinder barrels, a steel pin holds the bottom side of a plastic chain guide. This steel pin wiggles around and cuts through the aluminum. It can eventually cut all of the way through, but most likely it will first allow the timing chain to slip. Bad valve timing means the engine runs hot which leads to piston seizures which causes more damage. A work around the community settled on when rebuilding the engine is to simply JB Weld the gouge out hole closed, gluing the pin in place at the same time.

Tension on the timing chain is by spring. A large bolt on the crank case just behind the cylinder barrels contains this spring. Vacuum tension works better when it works but if you lose engine vacuum (eg the breather hose comes loose), it suddenly starts working far worse. In general, jumping time is a serious problem for this engine. If you get Z or N600, check to make sure that timing is correct. The manual has instructions. If the engine is running hot, check the timing.

Scans of the Honda service manual and parts catalog are online. The parts catalog is handy as a reference as it has larger and more blow-ups of how parts fit together. Print both of them, hole punch them, put them in a three ring binder, and keep them in your workshop.

Developing an exhaust leak or dropping your muffler makes your engine run way hotter and easily leads to seizing. The engine needs back pressure from the exhaust port.

Perhaps the most common cause of death of the Z600 and N600 engine involves the oil pump imploding. This was my experience trying to drive a Z600 home and was echoed by the community. These events happen in some order: The oil pump fails which starves the engine of oil. The top end is starved of oil so the camshaft starts chewing itself up (clogged screen on the oil pump intake due to accumulated metal shavings or one of the rubber primary/secondary drive vibration dampers breaks apart, or too much make-a-gasket material in the top end of the engine).

The oil pump is a piston design that's pumped by a piston attached to a piece of metal with a round hole in it. The piece of metal goes around part of the secondary drive that's off center. This piece of metal is made of aluminum. When it gets worn down a bit, the steel secondary drive shaft hammers it and it eventually shatters. This is a common way for the oil pump and the engine to fail. I have a hacked up one of these made out of steel, sourced from the community, in my rebuilt engine.

The oil pump can be accessed without taking the engine out of the car and without splitting the crank case open and coming face to face with your crank shaft, though taking off the exhaust parts and primary/secondary drive sprockets is still a major undertaking.

I've ordered a cylinder head temperature sensor to hopefully detect heat related problems before they cause critical damage.

1: The Honda Z600 and N600 (the Z being the sportier coupe version) were introduced to the US market in 1970 and removed in 1974 when the first Civic was introduced. They're relatively rare as build quality and reliability were not that great, they're prone to rusting, and they're far too small for American tastes. The original Civic, now considered ultra tiny, was significantly larger.

2: Often people stopped driving them and put them out to pasture to rust well within the period of time that Honda still had parts and service for these. People just didn't want to do the major engine work they needed. There are of course exceptions. This is speculation. Honda was also trying to introduce a very inexpensive car, not a high quality one. The quality that Honda became famous for on the Civic just wasn't there yet.

Addendum: Well, crud, I'd really like to do a nice little blog article here, but there are overgrown weeds in the yard from me going out of town and the neighbors are complaining, all sorts of other things are just bjorked up, I'm supposed to be doing a presentation, I need to be job hunting, and the motorcycle's floats are sticking again and I'll probably have to be in Chandler and other places if I do manage a job interview. So I'm just going to kind of vomit a few more things here without editing the first draft.

Doing this project, I spent a lot of time just reading stuff on line: how to adjust a carb (I kind of already knew before and you only ever kind of know how to unless you have a CO meter), how to break in an engine, how to repair a stripped bolt hole, what problems can lead to overheating in an air cooled engine, how to rebuild an engine, and so on.

The best how to adjust a carb tutorial was by Briggs and Straton, perhaps unsurprisingly. The best how to break in an engine tutorial I found was in the owners manual for a light aircraft engine. The how to rebuild an engine book I wound up reading was written in the 50's or 60's for navel deisel ship engine, and it took me quite a while before I figured that fact out when they started referring to Navel Command Bulletins and things like that. Nothing gave it a way for a while. I'm currently here on that one: enginemechanics.tpub.com/14076/css/14076_76.htm