dave88sw Posted July 13, 2015 Share Posted July 13, 2015 Hi, Can anyone tell me definitively what the differences are between a 2.25 and 2.5 petrol engine block? I'll elaborate, i have currently a very late 2.25 petrol from a 90 in my series 3 with the twin choke webber etc. It's in very good condition but i'd like a little more power. I still have the 2.25 that came out (late series 5 bearing but an imperial block not metric) and it's bores are oval and the crank a bit knackered. I also have a 12j na diesel engine that is virtually useless but has a decent crank etc. I have been looking at part numbers and the 2.5 diesel crank is the same part as a 2.5 petrol one so my theory was to rebore the old 2.25 petrol, fit 2.5 petrol pistons and use the 2.5 diesel crank and end up with a 2.5 petrol engine. My only problem is i don't know if there were any major block differences, i've read about oil cooling jets under the pistons on the 2.5? Is this true? Can anyone see any issues? Thanks Quote Link to comment Share on other sites More sharing options...
Gazzar Posted July 13, 2015 Share Posted July 13, 2015 That should work. but is the head able to take unleaded? I fitted a 2.5 head to my 2286 to get the hardened exhaust seats. And I'm planning on fitting a 2.5 to my lightweight. I can't see any major gotchas in that plan. You might have imperial v metric threads but that's hardly a show stopper. . Quote Link to comment Share on other sites More sharing options...
Daan Posted July 13, 2015 Share Posted July 13, 2015 Yes, this works; you will need to keep the connecting rods from the 2.25 petrol and use 2.5 petrol pistons. You also need to pull a core plug in the oil gallery, so the chain gets lubricated. starter and flywheel as per td engine, and block the oil feed for the turbo. Camshaft can stay as per td, the ingnition does fit to this as well. Mine worked very well this way for a number of years, good power , running on lpg. Daan Quote Link to comment Share on other sites More sharing options...
=jon= Posted July 15, 2015 Share Posted July 15, 2015 Bearing in mind that a decent 2.5 petrol can be picked up for an absolute pittance as nobody wants them, it may be cheaper to buy a complete engine than rebore / rebuild one from bits.... Quote Link to comment Share on other sites More sharing options...
Snagger Posted July 15, 2015 Share Posted July 15, 2015 Are the 2.25 and 2.5 rods the same? I thought they may be different lengths due to the longer throw of the 2.5 crank. Should be no issues with the crank and block, and oil jets for the pistons is an improvement, not a concern. Just be very careful with them - the banjo bolts are fragile and expensive, as are the jets. Quote Link to comment Share on other sites More sharing options...
dave88sw Posted July 15, 2015 Author Share Posted July 15, 2015 Thanks for the replies guys, very encouraging . I thought 2.25 and 2.5 petrol rods were different but what about the 2.5 na diesel rods, don't suppose they could be used with the 2.5 petrol pistons? I'd considered picking up another engine but they just aren't about, the only 2 breakers i've found with engines have wanted £300 each. I also wouldn't know the condition and would much rather have a fully rebuilt engine that will last. Cheers Dave Quote Link to comment Share on other sites More sharing options...
Lewis Posted July 15, 2015 Share Posted July 15, 2015 I scrapped a 2.5 petrol about two month ago, had I known there was any demand I would have gladly donated it to someone Quote Link to comment Share on other sites More sharing options...
Daan Posted July 15, 2015 Share Posted July 15, 2015 Thanks for the replies guys, very encouraging . I thought 2.25 and 2.5 petrol rods were different but what about the 2.5 na diesel rods, don't suppose they could be used with the 2.5 petrol pistons? I'd considered picking up another engine but they just aren't about, the only 2 breakers i've found with engines have wanted £300 each. I also wouldn't know the condition and would much rather have a fully rebuilt engine that will last. Cheers Dave You cannott use diesel connecting rods with petrol pistons, the piston pin is much larger on the diesel. 2.25 and 2.5 rods are the same length; the difference is in the piston Daan Quote Link to comment Share on other sites More sharing options...
dave88sw Posted July 15, 2015 Author Share Posted July 15, 2015 Brilliant, thanks for the info, in that case I have all the bits except the pistons but theyll have to be over sized following a rebore anyway. Last question then, is it worth keeping the 2.5 diesel flywheel and housing? I remember reading a tdi starter fits which would be easier to source and better than the old bendix starter. Cheers Quote Link to comment Share on other sites More sharing options...
Gazzar Posted July 16, 2015 Share Posted July 16, 2015 Yes, should/might also allow you install mega squirt crank sensor using timing mark aperture. G. Quote Link to comment Share on other sites More sharing options...
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