CBSE 12th

Hello Ajish,
The information you have given is quite interesting. You have scored quite well in your 10th, your 12th and even in your MBA. But while doing BE, something has happened which made you not score well. Oh. After you have finished MBA now you want to do Masters in mechanical engineering? Is that right? Yes, you can of course do it because you have scored more than 50%. You need to appear for GATE and depending on the marks obtained in GATE you can get an engineering college.
Normally speaking, your marks in BE should not matter much as compared with what you will get in GATE 2019, but which college and which university you will get depends to a large extent on how those scored better than you give their choice. So I suggest you should not think over it and just concentrate on clearing GATE2019, with very good marks to get admission in your desired college.

Hello,
If you want to pursue M.Sc from IITs/IISc through IIT JAM then you must have 55% aggregate marks at B.Sc. Level. If you satisfied the complete criteria then you can apply for JAM. If you have done your B.Sc in chemistry then I will suggest you prepare for IIT JAM Chemistry: https://goo.gl/F8vLLR
The basic criteria for JAM given below: -
IIT JAM 2019 is open to all nationals (Indian/Foreign). There is no age restriction, i.e. there is no IIT JAM age eligibility, regardless of your current age, you can apply for JAM. To apply for admission to the desired programme, a candidate is required to qualify in the corresponding Test Paper and also satisfy the Minimum Educational Qualifications (MEQs) and Eligibility Requirements (ERs) of the respective academic programme. The candidates who have either appeared or are due to appear in the final examination of their qualifying degree in 2019 are also eligible to appear in the test.