Dt175mx rumble in top gear

[Simon46]

I think I have a clue about this that has bugged me for a year. The chain permanently runs on the top of the  swingarm roller (new). I am not heavy so is my preload wrong on the rear shock or is it just how it is?

[Cynic]

Could be, as the weight comes on to the bike the chain, you would expect to lift clear of the roller and not run on it full time. Only when the suspension moves I would have thought.

Has the bike been jacked up? it was common back in the stone age for people to drill a new hole for the top shock mount lifting the suspension a few inches at the rear. I know cos I did it to mine when I was 17. That really gives the chain rollers and tensioner some work to do. Don't forget that one, the tensioner, they are notorious for seizing up.

 

[Simon46]

When I got it the shocker was mounted at the bolt hole in the frame to give it more lift. Its now in the proper position. Its horrible to ride in top gear but if I drop it down a gear its fine. The vibration comes right thru your bum

[Cynic]

Then check your chain  it may well also be the output shaft bearing, that's a bitch as its a full  strip to change, it only comes out from the inside and considered good practice to change whenever the gearbox is split for eg crank seals. Don't rule out wheel bearings and sprockets either.

Chain or output shaft bearing? if your lucky the chain would be my first choice as its cheapest but 6th is right near the bearing end of the shaft and that bearing leads a real hard life. Lots of loads, none consistent and stress from the chain (dried old chain lube, water, grit).

A good check would be oil leakage from the seal, commonly masked by chain lube.

[Simon46]

Going up from yambits newish did chain and sprocket kit to a wemoto bigger front +1( or +2 if it fits) to try reduce rubbing first

[Cynic]

My only consern with all this is that you say it only happens in top.

Chain or roller issues are generally full time.

Quick question. Pulling off in second. Do you get any vibes?

[Airhead]

Engine mountings tight?

[Simon46]

Rear mounting is split to hell with age. Powerband no problem. Low rpm it feels like it wants ro detonate 

[blackhat250]

Could be gearbox bearings,, My H2   did this,, it was the bearing  on the main shaft, [ behind sprocket] 

[Simon46]

Can you feel play if its worn?

[Cynic]

Possibly. Depends how badly its worn.

If its sending your arse numb i would think so. When i swapped mine out it felt horrible and that didnt show any vibes but was allowing gearbox oil to pass the seal.

[Simon46]

No drips but the yambits DID chain is stretched to hell. 700 miles from new! I know its 1.50 oversize and energy induction rt180 fitted. Can pull the links off the rear sprocket! 

[Cynic]

And what size are the sprockets then.

[Simon46]

Yambits 15 49

[Cynic]

What condition is the chain tensioner in.

[Simon46]

New nylon block fitted. Spring present and good tenion but had to threadlock the mounting bolt in as it would tighten then go loose as if thread stripped. 

[Cynic]

Ok.

Any chance of some pictures. Also how exactly do you tension the chain as 700 miles is ridiculous.

[Simon46]

Ok will get some up. Got the snailcams just set it to Haynes manual tension with the tensioner away iirc 20 mm slack and then apply the adjuster back to the chain 

[Airhead]

20mm slack!, now I'm a bit rusty here but...20mm, no wonder your chains fubard

yep, just looked in factory manual  40 - 50mm

[Cynic]

That means the vibes are coming from the front sproket and an almost certainly fubar outputshaft bearing.