DT 40 low compression

[don diego]

I bought this motor knowing it has low compression. 30 top 120 lower. What are best case, worse case condition of motor? Can I run this motor as is or will that damage it further?

 

[99yam40]

Re: DT 40 low compression

need to open it up to see what is wrong with it or at least us a bore scope to inspect cylinder and piston

I would not run it

 

[robert graham]

Re: DT 40 low compression

You could run a tank of fuel with deposit removal dosage of Ringfree to possibly free up carbon-stuck piston rings....then re-check compression....

 

[don diego]

Re: DT 40 low compression

By open it up do you mean remove the head or open the case?

 

[99yam40]

Re: DT 40 low compression

pull the head to see top of piston and cylinder wall

 

[Big_worm81]

Re: DT 40 low compression

... and then have a look at my thread for an idea of what you may be in for ...

My 1995 Suzuki DT55 Rebuild

 

[don diego]

Re: DT 40 low compression

Actually I had read your thread before I ever posted here. My two cylinder single carb 40 horse is a long way from your three cylinder three carb model.

 

[don diego]

Re: DT 40 low compression

I didn't have access to ringfree so I ran one pint of Seafoam in 1 1/2 gallons of no ethanol 87 octane. Ran at 1500 -1800 rpm til it was gone. Compression rose from 30 psi to 45 psi on the bad cylinder. Disassembled carb and blew everything out with air. Motor now starts at idle speed and will run at idle speed in gear.

 

[robert graham]

Re: DT 40 low compression

I didn't have access to ringfree so I ran one pint of Seafoam in 1 1/2 gallons of no ethanol 87 octane. Ran at 1500 -1800 rpm til it was gone. Compression rose from 30 psi to 45 psi on the bad cylinder. Disassembled carb and blew everything out with air. Motor now starts at idle speed and will run at idle speed in gear.

If your Seafoam/Decarb improved compression by 15 PSI then maybe do it again and see if it improves more....maybe piston rings are loosening up.....

 

[don diego]

Re: DT 40 low compression

If an engine has rings stuck to the point it loses compression does this allow enough space for the piston to hit the cylinder wall when it runs?

 

[robert graham]

Re: DT 40 low compression

If an engine has rings stuck to the point it loses compression does this allow enough space for the piston to hit the cylinder wall when it runs?

The piston rings ride in grooves in the piston and they are springy and they flex and ride against the cylinder walls creating a tight seal for the compression...if they are stuck in their grooves with carbon and they can't flex, then you'll lose compression.....Maybe and hopefully your Seafoam treatment is helping loosen up the rings....Check a product called Yamaha Ringfree, a product that you add to your fuel to help prevent ring sticking....