Break point for rings/deglaze and full rebuild/replacement? '95 3.

[WesBrooks]

Morning,

Fishing for a little information ahead of time again.

Compression is down on my engine and as I intend to MegaSquirt it (I see there is plenty of experience on these forums and a friend has built one up for a Celica GT4 - so I should be capable!) a within spec starting point would help matters significantly!

So the engine (if original which I think is the case) has completed 150,000 miles. It has had it's fair share of miles and suffered some poor maintenance, at least recently. So I'm estimating a full rebuild is in the order of £2000 including help for installing liners and I guess a couple of extra tools, not that far off buying a ready built short or long block.

Is de glazing the bores and rebuilding with new gaskets where disturbed a resonable option? So long as the valves on the heads aren't badly burnt or recessed are there other things to check before doing that? ...or is the effort of doing that not that much less work/money than the rebuild/replacement route? Are there other wear/condition indicators to check for that would help decide which is the most sensible approach?

Cheers,

Wesley.

[FridgeFreezer]

The thread title got cut off, what block are we talking about here?

If it's a standard 3.5 or even 3.9 with no major issues (as in it's just worn & has a leaky head gasket) I would really not bother spending big bucks on it, you may as well track down a 4.0 or 4.6 and spend the money building one of those up as they're a nicer base to start from and will appreciate the top-hat liners. Or for cheaper, just give your old lump a good refresh with maybe a lumpy cam and run it. £500-£750 in parts depending how meticulous you're being.

The technical archive has (or had) an excellent thread by Bull Bar Cowboy on rebuilding a 3.9.

[Les Henson]

You can get a good guess at bore wear by looking at the step at the top of each bore. There's a narrow ring that is the distance between the top piston ring and the top of the bore. Clean any carbon off before looking. Bores tend to wear slightly oval as well, and to check that and ring gap, you need a new ring and push it about a 3rd of the way down the bore with a piston (to ensure it's dead square). You then can check bore ovality by looking for a gap between the edge of the ring and the bore. Also measure the ring gap to see if it's within specs. If the bore isn't too badly worn, then oversize pistons and the bores machined to match them would be a cheaper option, and you would in effect have factory compression restored.

Les.

[WesBrooks]

I'll have a look for that thanks.

Yeah I appreciate the thought behind the 4.6 route. That's the ultimate plan. I'm wondering whether I can get by with a refresh to the serpentine 3.9 or whether the costs are likely to get close to rebuilding. As I'm typing it seems a light refresh on a 4.6 and later rebuild would be more sensible.

Symptoms are low compression (140-150psi), sticky idle valve, leaky inlet manifold, and leaky everything. It's had OAT coolant in it so needs many seals replacing! Exhaust manifold bolts were finger tight!

[WesBrooks]

Ok initial strip part way through.

It looks like the engine has had a rebuild in it's life time but I'm not sure how recent that was. How long would you expect the honing / de-glazing marks to last from the previous rebuild? In addition to that the water pump had a lot of clear silicone in it, and many of the bolts were just finger tight, requiring just a socket and extention for a little better grip to undo.

On the up side the head was tightly bolted down and the bolts seemed even. I was using a breaker bar to undo them so I could feel what they were like. All of them cracked loose making the same sound, and feeling about the same tightness. No signs of leakage beween the cylinders and the liners look like they've stayed put.

Honing marks:

Cam looks toasted. It's got the brown in the middle and shiny on the outside wear pattern. A couple of the lobes looked pitted. The followers looked smooth, but with a central patch of wear as well.

Toasted cam lobe:

There's a lobe on here though that doesn't look too bad?

Not checked the step at the top of the bore yet, and not checked the mains. Sump is currently still on!

I'm guessing my bill of materials so far is cam, cam bearings, followers, rods, timing gear, timing chain, water pump, and most likely rockers - as well as the usual service items and gaskets where disturbed. I'll have a look at the mains next weekend.

What do you think? Perhaps a cam swap without followers being changed, or a poor cam run in? The followers weren't mushroomed on the lobe contact face and slid easily out of their bores. I'm aware there is a fair bit of muck about. I'll get the engine spotless before rebuild and install.