1982 XS400 DOHC camshafts spin directly in the head! WTF?

[CrazyCabbie]

I recently found out that the cams on the DOHC sit directly in the aluminum head.
That just seems like a huge wear problem waiting to happen.

It sure has on mine... Finally took a good look.
There's so much wear that the cams rattle around in there...
In thinking now that the initial knock I heard was no upper lubrication, leading to the extreme wear because (IMHO) running cams on straight aluminum is just stupid...

Can someone that knows engines explain why the cam runs in aluminum with no babbit bearings? That seems soooo wrong to me (it's what's knocking on my gutless 80,000km DOHC)

Is this the something they did so we can't just ride them forever?

 

[Scorpio1963]

I brought this issue up about the sohc engine it was supposed to be a fool proof design claiming that there was always a constant film of oil that kept the aluminum from wearing out.I also thought it was a stupid design no bearings then it wears out you have to replace the case.Might cost some some cash but I would machine the surface large enough to roll on a clamshell bearing.

 

[xschris]

Nothing lasts forever These bikes where low cost beginner bikes anyway not designed to last for 100k miles I have 30500 miles on my 79 with all original top end and still runs fine I think with good maintenance and don't beat the crap out of them you could see 40-50k miles. Also remember these are 35+ years old.

 

[CrazyCabbie]

Scorpio, my thoughts exactly. Thanks.

Chris, you're just basically telling me I'm fucked... Not really helping.
Every vehicle I've owned but one was something that someone else said was unfixable, and I put about 500,000 on every japanese car/truck engine I've ever owned before they weren't servicable, so I expected more for the putt-putt way I drive.
I know it's not an automobile but I'd like to be optimistic.

 

[16VGTIDave]

Really? This is a proven design used by most every engine manufacturer, including every car or truck you've owned. Now, if you'd like to pay lots more, for an exotic design with bearings that won't last any longer that what you have, please wave your money in the air and shout out... What's that? Silence? I thought so.

Think about the simplicity of the design. The lack of parts to design, fabricate, install, and stock for a minimum of 7 years. The oil film bearing is very efficient and effective. Roller bearings would still require lubrication, and have more than double the friction with less load carrying capabilities.

Repairing the cam journals is easy for any decent machine shop. Remove some material from the mating surfaces and then align bore back to the stock dimensions. No parts required.

Bottom line - This is a sound design. Your appreciation of this fact is not required.

 

[CrazyCabbie]

Dave, why the condescending tone? I admitted I didnt know what I'm doing, and my first impression is that it should have babbits over the cams, because I've only ever seen steel-on-steel cam 'friction surfaces'.. I've had them apart, I've seen the steel inserts in my aluminum 22R head.
I was actually looking for that exact information and appreciate the excellent information that you always provide. If I didn't appreciate the design I wouldn't have bought it.
What I don't appreciate is being made to feel like an asshole.
Thanks anyways, I guess...

 

[16VGTIDave]

Blame it on the coffee, the long day of work, all the idiots on the road tonite, or that I'm not going to get to Port Dover tomorrow, but I'm obviously cranky. If you re-read your posts from an informed perspective, you might just be almost as annoyed by your tone as I was. Add the fact that this has been debated earlier this year, and I got my hackles up.

Regardless, I didn't intend to insult you despite my harsh tone, so please accept my apologies.

Now, I'm going to get back to work so that I can still have Saturday off to attend the cruise I've organized...

 

[willem]

B*tchfight!!!

but seriously, I'm guessing the designers had about 80k km in mind for the xs400 as a maximum lifespan. I was also surprised about the (over-) simplicity of the design, but these bikes are, and have been from the start, the poor man's transport. Nonetheless they are loads of fun, but you don't expect a $2 screwdriver to last forever either.

I'd say every km it lasts over 75k is a bonus..

(mine is at 85k km )

 

[xschris]

I would start looking for another spare engine with low miles to keep as a back up. I have three I keep for myself Remember these bikes new sold for $1300 or so. Unless you bought it new and took super great care of it they won't last. Sorry your so mad about it but that's just how it is

 

[Scorpio1963]

Im with crazycabbie on this one I have never seen any other engine that didn't use trimetal surface on bearings for a camshaft.Most that have last well over 200k miles.If the design can be improved by some modifications from a machine shop then why not use it.The only other setback I see is matching the bearing that should be too hard to do.Will it be cheaper than getting a spare engine IDK nobody has ever done it that I know of.Dave you mention a roller bearing still needing lubrication your right but so will any other bearing design.If I were a betting man I bet it can be fixed and made to last longer for $150.
Then you run into another problem with rod bearings wearing out but that's a whole another topic.
Cabbie if you decide to do this please take some picsave one last fact being brought up.You say every car engine is designed this way are you talking about a camshaft that doesn't use a sbearing surface and runs directly on a aluminum or steel engine block?If so name a few.

 

[CrazyCabbie]

Thanks & sorry Dave, hehe , had a pretty stressful day myself...

Well that sucks.... I have a spare low mileage head here, just figured I could throw it on and get another year or three, but if the entire engine is designed to wear out that low it wouldn't be worth the effort.

If I ever saw a decent used one around for $1300 I'd probably run straight to the bank...
There is one in mississauga for $1700... Should bought that before I wasted so much money trying to fix the damn thing...crap.,,

 

[xschris]

People need to remember how many rpm's these little air cooled engines run. Try running a car at 7-9000 rpms and see how long it lasts If you are looking to drive long distances get a honda gold wing they are good for 80k+ miles.

 

[willem]

I believe my Seca can get to the 100k km mark.. at least! and at this rate it'll be there pretty soon

 

[HoughMade]

I think you hit upon the real issue in the initial post. As long as the lubrication keeps flowing, this is no problem (22,000 miles and running strong). The problem is an owner maintenance issue (a previous owner, I mean). Too many people are used to "gas-and-go" these days and these bikes require regular maintenance. If a guy runs the recommended oil, checks it every ride, changes it at the recommended interval (or before), keeps the carbs adjusted so it doesn't run lean, and keeps gas out of the oil, these things will last a good while.

When bikes sit for years, are run without the proper oil or clean oil, (I have heard of numerous stories in this forum of people starting up and running bikes with the oil that sat in them for years......c'mon), when oil is topped off but never changed, when oil gets s too hot because the bike is run too hard, too often and lean....there are going to be problems.

 

[16VGTIDave]

Well that sucks.... I have a spare low mileage head here, just figured I could throw it on and get another year or three, but if the entire engine is designed to wear out that low it wouldn't be worth the effort.

On the contrary! It is the simplicity of the engine design that will make it last! With regular and proper maintenance of course. I've had numerous engines that use a similar design SOHC and DOHC "cam and bucket" head (mid 80's VW's) that have withstood 300k - 600k km each of street and track abuse without a single camshaft failure. Literally hours at a time run at the redline, bouncing off the rev limiter with the oil temp over 120C. And then driven home and to work the next day.

As long as the oil is free of debris and maintains pressure, the camshaft and it's bearings will never touch and never wear. Lose oil pressure or flow (like I'm thinking your engine did), and no bearing will survive. And like I said, it is reasonably easy for a machine shop to repair the cam bearings.

It is the simplicity and ease of maintenance that have our bikes still on the road after 30+ years.

 

[xschris]

Agree with hough Also 80000km's = 49709.7 miles I keep forgetting to convert because 80000 miles is a lot for any small cc bike. With them many miles I would think a cam isn't the only thing worn out in the engine and making it gutless