85 250es rattling chain when cold

[Epic69]

I have a 85 250es big red. Cam Chain clanking when engine is cold, once engine warms up good sounds good. Would it be best to just get a new camchain tensioner off ebay or maybe with a manual cam chain tensioner?

[shortline10]

This is a mod that I have been doing for years on the 85 250sx/es models .

Remove the small end cap on the tensioner and install a longer one / piece of steel tubing .

This mod also works on the 86 model 250’s and Trx300fw fourtrax all years but you’ll need to purchase an 85 style tensioner , 86 and up uses a crimp on cap and can’t be extended .
Works very well .

The manual tensioners are crap imo and don’t recommend them .

[smoknrv4]

How long is the new tube you put on? Thanks for the info!

[shortline10]

I believe around 35mm



How long is the new tube you put on? Thanks for the info!

[MrConcdid]

Yep, this is mine, Shortline, saved the day.
I used a piece of automotive 3/8 metal fuel line drilled it and welded the end solid then ground it down and rounded the edges.
Fit perfectly.

MrC

[atc500x]

Why not changing chain??

In my book when the tensionner can't do the job it's because the chain need to be changed...no??

[big specht]

I’m with you on that just change it. it’s more than likely a 35year old chain and the clutches need changed and valves need adjusted too.

[shortline10]

Why ?
Because it’s a huge job to pull the head and right side cover to replace the guides and cam chain . I have done hundreds of them .
IMO the cam tensioners were made way to short from the factory and this just give the motor a little more time before that big service needs to be done .

[atc500x]

big job...2-3 hour and it's done.I prefer changing the chain than a broke chain and bent valve and need a complere topend rebuilt.It's a normal maintenance after 35 year,and when tensionner can't do the job,keep in mind the chain is too long,and the timing between crankshaft and cam isn't perfect,engine run WAY better with a new chain.

[shortline10]

Can not be done in 2 hours lol , obviously you have no clue what’s involved to service it completely. I have been a power sports mechanic for over 33 years and have rebuilt hundreds of these motors .
I’m not talking about just pulling the valve cover and sliding a new chain down around the crankshaft .
Yes the right way is to pull the whole top end and service that , valve job exc . Pulling the right side cover and serving the clutch as well . All that can not be done in even 3 hours .
I showed this simple fix to show people how to get a little more life out of a timing chain , that imo like I said the tensioners were made to short .
Most are usually beyond the point were this simple fix works , worn out guides etc but it does work well when the only problem is a slightly noisy timing chain issue .



big job...2-3 hour and it's done.I prefer changing the chain than a broke chain and bent valve and need a complere topend rebuilt.It's a normal maintenance after 35 year,and when tensionner can't do the job,keep in mind the chain is too long,and the timing between crankshaft and cam isn't perfect,engine run WAY better with a new chain.

[atc500x]

Don'nt be worry,I change thoses chain about 10 time every summer,I have also a shop.3 hour is what I charge to change a chain if there is no broken bolt on the valve cover

[350for350]

Epic69, before you go about changing the cam chain or something else, why don't you check your valve clearances? My 350X was doing the same thing. It would be quiet when cold, but it would have a slight rattle when it got warmed up. Last night, I set the valve clearances, took it out for a test ride of 7-8 miles, and it was still running quietly with no rattle when I got done with the ride. It may not help, but it may.

[kb0nly]

I've done that tensioner mod that Shortline posted, its well worth a shot if you got one thats just getting a bit noisy. I agree with him on them being too short, there is a big difference between a really worn chain and guides and one thats just making a small amount of noise because of the tension on it. If you extend the tensioner and its still noisy then its time to replace it, otherwise i have done cam chain on these before as well. 2-3 hours?? How? If you do it right its not going to happen that quick, if you do a sloppy makeshift job of it then perhaps you can do it that fast. I have seen crappy chain replacements done by a local shop with rtv instead of gaskets and the timing off a tooth or two. I agree with Shortline on that, if you can change a chain and do everything right in two hours then you should be offering it as a service because i don't see it happening.

Again, this mod works for a slightly worn chain and guides, its not a fix for a worn out chain. I have heard a lot of 250's, back when i used to buy and sell trikes to flip em for cash i would do this mod if they had just a bit of noise and let the buyer know it was done and that if the chain gets noisy again then its time for a rebuild. But some of the ones i modified are still running just fine going on almost 10 years later!! Some of them see regular daily farm use chasing the cattle around and such. So they couldn't have been that badly worn if the tensioner mod quieted them down for this long.

It can be done really simply as shown, i turn down solid rod and make them on the lathe, but either way works.

[th67ss]

Will an 85 tensioner fit a 86 250sx?

[shortline10]

Will an 85 tensioner fit a 86 250sx?


Yes it will fit

[th67ss]

Ok Thanks!

I thought it would just wanted to make sure.

[redskinman]

Does the end piece need to be completely smooth{like example pics in thread} or can it just have the tube on end like I've done? thanks

[shortline10]

Looks good , I just take the sharp edge off the tubing , I don’t bother with the original cap .

[redskinman]

Looks good , I just take the sharp edge off the tubing , I don’t bother with the original cap .

ok thanks thanks