12 replies to this topic

[Risky]

About 4,5 years ago, when I replaced my first engine, I was quite excited to see how an engine was built, so I dismantled the old engine. Took everything out to rebuild it some time in the future.

 

Now after some years alle the parts have been moved several times and nothing was labelled or numbered unfortunately. So I don't know which bearing caps should go where and also no idea about the pistons etc...

 

My question: Is is still possible to rebuild te engine? I've worked on aviation engines for 1,5 years and I learned that every cylinder should normally have its own piston (only when not replacing a cylinder or piston - so cylinder no.1 should have piston no.1 etc).

 

The idea is to inspect everything, use new crankshaft and big end bearings, new camshaft, new piston rings (or new pistons if the block has to be rebored) and replacing the small stuff like bearings etc...

 

Thanks in advance!

[coopdog]

Yeah it's very easy, you'll need all new bearings anyway,

All there is to it is pistons,con rod and crack pretty much haha

Just watch some videos on YouTube and get an idea of what everything looks like

[myredmini]

Not as easy as you think.. the caps need to go in exactly the same orientation as it was made due to them being line bored.

Not sure how this is rectified but im sure someone will be along soon to explain.

[carbon]

Would be helpful to know age and cc of the engine.

 

First do you still have 3 main bearing caps to go with the block?

 

Second do you have 4 big-end caps, one to go with each rod?

 

And third have pistons been taken off the rods?

[Tamworthbay]

You can work it out if you have access to quality measuring kit. This won't help this time, but it's worth using a punch to mark each cap with its position, 1 dot = no1 piston etc, Mark them all the same side and you know which way around as well.

[Bubblebobble]

Perhaps a machine shop would be able to accurately measure and match up the caps for you .

[Risky]

Forgot to say which engine..

 

- 998cc A+ unit (1981)

- pistons are still on the rods

- 3 main bearing caps which are from this block

- got 4 big-end caps, but don't know which cap belongs to which con-rod

 

Machine shop is a possibility, but quite expensive I'm afraid... I don't have access to quality measuring equipment anymore unfortunately...

Edited by Risky, 28 February 2015 - 06:37 PM.

[Bubblebobble]

Im sure you know that its pointless putting it back together if you have not measured , assessed , reworked  and matched the parts correctly .

[Risky]

Just found this pic from after dismantling. Fortunately the caps are still with the rods. If I use new bearings everywhere and new piston rings it should be OK.

 

Only problem left is de main bearing caps.

 

 

[carbon]

Risky,

 

OK, easy bit first. The three main bearing caps :

- one with recess for thrust washers is middle

- one with two drilled & tapped 1/4 holes is timing end

- the other is flywheel end

 

Now for the con-rods and caps. This is process of trial and error, but if the bearing shells are still in caps and rods it may be easier - look for any witness marks (ie tiny grooves) in the bearing shells and then if you can find corresponding other half this may be a pair.

 

Otherwise you will need to assemble each cap onto a rod in turn, and then check for any offset in the fit between the rod and cap. Once you get the right pair they will line up perfectly - but this may take quite a few tries before you get this right.

 

As mentioned above, marking up the rods and caps before disassembly saves a lot of hassle later...

[Risky]

Risky,

 

OK, easy bit first. The three main bearing caps :

- one with recess for thrust washers is middle

- one with two drilled & tapped 1/4 holes is timing end

- the other is flywheel end

 

Now for the con-rods and caps. This is process of trial and error, but if the bearing shells are still in caps and rods it may be easier - look for any witness marks (ie tiny grooves) in the bearing shells and then if you can find corresponding other half this may be a pair.

 

Otherwise you will need to assemble each cap onto a rod in turn, and then check for any offset in the fit between the rod and cap. Once you get the right pair they will line up perfectly - but this may take quite a few tries before you get this right.

 

As mentioned above, marking up the rods and caps before disassembly saves a lot of hassle later...

 

Great info, thanks! Will take my time to sort everything out before I start the rebuild. And yes, next time I will mark all the parts ;)

[Ethel]

It matters because they are machined as assemblies, so close inspection with a magnifying glass may reveal witness marks from the machining you can match up.

[Spider]

The Main Bearing Caps are a piece of cake.

 

OK, all bearing caps fit together 'tang to tang', that is the small cutouts for indexing the bearings shells, they meet up on the same side, this also goes for the Big Ends.

 

The centre one is the only one that has thrusts.

 

The front one also was a face machined flat and lines up with the front of the block for the front engine plate

 

The last one left is the back end cap.

 

Now, on the Big Ends, you can usually pick which is which by trial assembly. Normally if it is the wrong cap, there will be a step in the tunnel when fitted together.

 

If you find that you end up with two that you are not sure about, it may mean having those measured to be sure.

 

In any case, I'd have the rods 'Closed and Honed' not because of any mix up, but that's it's normal engine rebuilding practice. They do get out of round.