2500S engine swap opinions

[llessur]

Engine's already out and on a stand 😉

[llessur]

Right, had another look at the block today - cracked four of the big end caps to see what lay beneath. And to be honest the story wasn't quite as good as the main bearings.

All four had noticeable scoring to the bearing shells but more worryingly had more obvious scoring to the crank journals than with the mains. This time it could be felt with a fingernail - not deep ridges, but still noticeable slight undulations in the journal surface.

Big End 1

 

Big End 2

 

Big End 5

 

Big End 6

 

So, obviously not as good news as I had hoped but given that I'm not an expert in engine rebuilding I'd be interested in any suggestions as to how to proceed.

If the budget won't stretch to a rebuild (which it most likely won't), given the low mileage I'll be doing I'll still probably swap out the mains and thrusts and just use the engine as-is but what would would be the best course of action with the big ends? Given the wear to the crank journals am I asking for trouble if I put new bearing shells in? Would I be better letting sleeping dogs lie and just leave the old ones in place exactly as they came out or would slipping new ones in do no harm?

 

[Clive]

The slight scoring is not great, but a fresh set of bearings will make things a little better. And for the cost would be wise. (sets are about £25 or so?)

You will probably keep it going as is for many more miles. No warranty implied or given!

 

[llessur]

Cheers Clive - I'll send the warranty claims to your house 😉

I'm back in the motherland for a couple of weeks in Jan so I'm planning on putting in a Chris Witor order and making the most of my luggage allowance for the return journey. Will pick up some standard mains and big ends and a small assortment of thrusts along with some suspension bits and bobs.

I've got a second 2.5 block in the garage which I think is likely in similar or worse condition to this one. I'll stick it on the stand when I've got time just to make sure it's not the better option but it had been run without an oil filter when I got it so I reckon it'll have fared worse.

I'll give the best of the two blocks a quick refresh in the short term to get me on the road. I can gradually strip the other one down and get whatever machining needs doing done when time and money allows so that I've got a rebuilt lump to drop in a few years from now. 

I've never done a full engine rebuild so it'll be a nice project.

[Nick Jones]

I’m pretty much with Clive on that.

Really those BEs are shot & need grinding. Someone has already done what you’re thinking of doing. However, if you are just going to potter about and not do many miles, you could stick some new shells in and it’ll go on for years - if you don’t rag it. Rag it and it’ll soon die. I’d suggest alu/tin shells .....

On the other hand, right now you could just lift the crank out and get it ground. BEs only even, if the mains measure right. Then the doubt is cleared......  Wouldn’t be big bucks here..... dunno about where you are?

Nick

[Colin Lindsay]

13 minutes ago, Nick Jones said:

 However, if you are just going to potter about and not do many miles, you could stick some new shells in and it’ll go on for years - if you don’t rag it. Rag it and it’ll soon die.

That's something I'd agree with - new bearing shells and the car will go on for quite a few more miles yet. It all depends on how much use the car will get; if it's just pottering about then no worries; faster use or bigger miles may point towards getting grinding work done now while the engine is out. 

[llessur]

Not sure on the price of a grind but stuff tends to be expensive out here in Oz - might ring around on Monday to find out. But then it's the slippery slope - if I have the crank ground, whilst that's out I might as well strip the rest of the block down and have the bores sorted and stick new pistons and rings in. Leave the head for another time...

Will have a think about it over the weekend - my mileage will probably be quite low overall but individual journeys might be 100km or so return, including some freeway driving.

Budget is low so the thought of doing a cheap and cheerful refresh now is very tempting, but deep down the idea of putting the engine back in knowing it's got a problem doesn't sit well with me...

[johny]

Save your money unless youre planning on some racing or lots of miles! If youre worried you could micrometer up the journals for out of round which in my opinion is much more likely to prematurely finish off bearings than the surface itself (within limits of course!).  

[llessur]

Am still leaning towards doing a quick tart-up at this stage but just hypothetically if I decided to 'go nuclear' and rebuild the engine I'd like to do the dismantling and reassembly work myself. Whilst I've not rebuilt an engine before I'm fairly confident with my ability to follow the factory manuals, work to specs/tolerances, maintain cleanliness etc.

Ignoring the head for a bit and just thinking about the block, what's the minimum amount of work that I'd need to outsource? Just the machining, or does any of the reassembly ideally need to be done by an engine shop? Can I get away with taking in a stripped block, getting it honed or rebored as required, getting the crank ground and then taking it all back home to reassemble? Or is that overly simplistic?

At what point is skirt clearance determined? Does the machine shop measure the new pistons prior to boring and then bore the cylinders accordingly?

 

 

[dougbgt6]

You are correct, just the re-bore and re-grind. Reassembly is quite simple, the first time I did it I was a complete novice. Just follow the manual.

The machine shop will decide how much is needed to be removed, this will be in 10 thou increments. They will bore 10 thou or 20 or 30 over size, depending on wear. Then you buy oversize pistons, 10, 20, 30 thou to match.

When I’ve had it done the machine shop got the pistons, rings and bearings for me.

The trickiest bit was getting the pistons and their rings into the bores, there is a tool for it, but it can be done with screwdrivers.

Doug

[Nick Jones]

Don’t use screwdrivers.......

Piston ring compressors are neither complex nor expensive - if really can’t lay hand on a ring compressor then a suitably sized jubilee clip and a rolled strip of sheet metal will suffice.

Dependent on bore wear levels an intermediate step is to hone the bores and fit new rings only.

If it ran well before and didn’t smoke/ use oil, leave the pistons in situ and just attend to the crank.

Nick

[llessur]

So after a weekend of musing my plan of action is to do a leak-down test on the engine to see what the piston rings and bores might be up to. It wasn't noticeably smokey but I only did a few km in it before the car was broken for parts so I wouldn't say I trust it completely. I wish I'd done a compression test on it whilst it was up and running but time was limited to strip the car and get it off the driveway. The benefit of hindsight and all that...

If all goes well I'll probably go a step further in my refresh and get the crank main and big end journals ground - I have rung around a couple of reputable local machine shops and this would come in at around the $200 mark (£100) including crack testing so not too bad really.

If the leak-down test results aren't good then I'll think again about my options.

If I did decide to rebuild then getting the block rebored is around $360 (£190) at the machine shop including honing and decking.

Then I could rebuild the block myself, leaving any head work for another time.

So with new pistons, rings, bearing shells, gaskets etc that'll be a total outlay of around $1000 (£500) which I don't think is too bad but still a little more than I had budgeted for at this stage.

In reality if the bores are toast then I might just chuck in some new thrusts and bearing shells for now and run it until it dies. I can concentrate on stripping and rebuilding my spare block over time in readiness.

[llessur]

I did a leak-down test today and seems there's quite a lot of leakage - the gauge showed around 40-45% leakage on each cylinder, most of which seemed to be coming up around the pushrod area so presumably it's getting past the rings. There was a small hiss from the dipstick tube and a little bit from around the valves too. Each cylinder was at TDC for the test, compressor supply PSI was around 90.

I'm not 100% sure how much to read into this given that the engine was cold and hadn't run for a year or so but I'm thinking I'm going to bite the bullet and strip it down for a rebuild anyway. 

I know I could probably just chuck in some new bearings and run as-is for a long time yet but working on my own around parenting responsibilities means that taking the engine out and getting it back in again realistically results in the car being off the road for months. I'd therefore like to know that once the engine goes back in it hopefully won't need to come back out again for any reason for a long time. That'll hopefully be the case if it's rebuilt. 

I'll get the machine shop to do the bores and the crank and I'll aim to rebuild at home as and when time allows.