Good day...
I'm working on an absolute beater DT 250, plan is to prep it for AHRMA Vintage XC racing.
The engine needs to be pulled.
All fine except for the top rear engine mount bolt.
Apparently the 8mm bolt fits through a steel sleeve between 2 rubber "dampers".
This bolt is NOT moving. Steel bolt in steel sleeve...must be plenty of rust.
Yes...I've dealt with stuck rusted bolts for decades so I know most of the tricks, however:
Before I take to the Sawsall or a hack saw blade, which will not help getting the remains of the bolt out of the sleeve...
Any suggestions from those that have dealt with this issue?
I appreciate any advice.

How about drilling the bolt out of the sleeve portion of the bushing? Then you might be able to drive the rest of the bolt out of the motor. May have to take a die grinder and remove the sleeve from the rubber bushing. If the bolt is seized in the motor then that's another problem. I know this sounds extreme, but when you feel you have tried everything else. I just went through something similar on the brake anchor on a DT3 and had to use the sawsall to cut the bolt and then remove the bushing. Never did get the bolt out of the bushing.

It's helpful to state the year model. My guess is you have a 77-on monoshock as I don't believe the earlier models had the rubber mounts and steel sleeve...

Not sure if you're saying bolt won't spin or won't press out... if it won't spin, I use an electric impact wrench to shock it. Extreme case you can drill a small hole in center of case directly above bolt to get penetrating oil in there. Fill and let sit a few days.

If bolt spins but won't press out then an air chisel with a punch tip often works.

If bushings are damaged/destroyed you can make aluminum bushings for case like the 1977 IT175 had.

How about getting someone to hold a heavy steel tube over the head, pushing hard, or over on its side on the concrete, so mount is well supported. Then with a steel something against the thread & give the steel thing a god hit. It'll move. Could the flip it over & go the other way. Then next hit it'll probably give in. [or rivet over--hope not]. Shock treatment works for me, but has to be an unhindered possitive shock, not rubbery soft like. Swinging arm bolts are my favourites.

 Here's my trick for swinging arm bolts. Maybe run the nut on yours although might not help. It's gonna be beyond use in the end but at least it'll be out. Desperate means i know haha.

Working on these old bikes...we've all come up with situations like this...thanks for the suggestions. The bike is a 1974 DT250A to clarify.
Turning the 13mm bolt head with a wrench only turns the rubber "damper" bushings in the engine. That 8mm steel bolt is just solidly "rust welded" to either the inner steel sleeves of the 2 bushings, or to the spacer sleeve that sits between the 2 bushings...or perhaps to both! For now I'll continue to dribble PB down the bolt shaft as often as I can...give it a few hammer/punch blows from time to time...and give it a few days. If I DO end up cutting the bolt (at both ends) to remove the engine) the only benefit is I will be able to lay the cases on their side...allowing more PB to penetrate...and then be able to hammer DOWN instead of horizontally as I'm doing now with the bike on the lift. And perhaps take the cases to a friend with a press...I'll try to post a photo later.

Looking at that photo by RT325...I think before I cut away...I'll take the bike down off the lift.
Take it outside, lay it on it's side...then more PB that perhaps can then sink in for a few days.
Set up the appropriate bracing to the l/h frame tab...and then better force on the hammer/punch...

Well...I did do a set up as RT325 suggested. Bike on it's side. Steel plate and steel tube supporting l/h top rear frame tab. A ton of PB. Not a hammer...but the sledge hammer. Nada. Ziltch. Zip. no movement at all.
So back onto the lift, and out with the hack-saw blade.
Question: Does anyone have any of the bushings and a center spacer tube?

Damn, well that's dissapointing. let me at it lol.

Update: Fresh 18 tpi metal blades for the Skilsaw. Cut both on inside of frame tubes. Engine on bench. OK, now what?? Center punched bolt....didn't get it dead center...but close. Drill away. At a point when I thought I was deeper then one of the bushings, I was able to drive out the opposite side with a thin punch. Split cases. Center spacer is rusty but bolt was NOT stuck there. It was "rust seized" in the 2 bushings. So...I can clean up and re-use the center steel spacer. Now just need to find some new (or good used) bushings.