Need help fixing bike!

[kellanphil]

Hello my dad has had this bike since new I believe it's a 1990 or 91. Many years ago the oil plug fell out and it got ridden for a bit with no oil and my dad said it lost compression and had no power. We did find a New Old Stock piston. Do you think a pistonand rebore is enough to fix this bike? from what he remembers there was no weird sounds or anything other than the bike lacked power. I'm just trying to fix it up for him a little bit and get it running again. Is it correct that all the Dr 800 Pistons are the same?

[Bambi]

Hello and welcome!
Is Phil your name? And where are you from? There's a whole lot of countries where the Big is not known very much, even to dealers.
What usually fails first if the DR Big is ridden without oil is the valve train. I'm no big expert concerning an engine overhaul but I'm pretty sure that you have to dismantle the whole engine to look if there's wear and debris in it.
I think, that our more experienced users will show up soon for real help and advice.
Kind regards, Bambi

[LuluBanane]

Hi,
is it a SR41 (DR 750), SR42 (DR800 two tanks) or SR43(DR 800 Single Tank) ?
Piston from SR41 and SR43 differ, but you can replace a SR41 piston with a SR43 but not vice versa.
Have you checked compression already and did a look in the cylinder if there are any marks or scratches?
Check also the camshaft, maybe is it damaged also and that causes the lack of compression. If the coating of the cams has gone you have to replace it.

There is no sleeve in the cylinder, if the scratches are to heavy you have to drill out (rebore ?) and use a piston with a bigger size.
This guy can help you https://www.dr-big-shop.de/BIG_MotorHaupt.html o rnew shop https://hessler-motorsport.de/kat/dr-area/dr-big/ use googe translator He sends parts all over the world

Best regards
Lutz

[Knarf]

Hey kellanphil,

first things first - I think you're right here for "first aid"!

As Lutz already mentioned details are essential. Mentioning 1990/1991 provides too many options, so just check the label on the right hand side of the steering rod (on the frame). This should give you the model (SR41/42 ...). Another important information is the trip-meter (how much km or miles does it show)-
Regardless of the model, check the compression - as Lutz also suggested! Those compression tester cost almost no money and they're quite useful (often required for servicing) for this old lady. In case compression is below the threshold (manual), add some oil through the spark plug bore and measure again. If you're above the threshold chances are good that new piston rings and sealing should do the trick.
Anyway you'd have to remove the cylinder head etc. and also might find some nasty scratches in the bore of the cylinder... We're talking about mechanical issues, so basically; no worries!

Last but not least, this forum is quite like a family so it would be really nice if you just briefly introduce yourself by creating a new "Fred" clicking HERE.

Cheers and good luck!
steph

[Lackmichel]

Oh the Uncle Knarf