Engine inspection, scratches

[Grid]

Is it normal on the 6A13TT for the piston bores to have such marks on the walls? It is not possible to feel those discolorations while running a finger over them. All three rear bank bores have these. The front ones don't.

Well anyway the engine will be stripped further, just wondering if anybody saw anything similar.

 

[Grey_Ghost]

I had a failed thrust bearing and crankwalk. It usually sounded like piston slap.

 

[6A13TT TYPE S]

Bores look normal. But jesus those pistons have seen some detonation

 

[Grid]

Bores look normal. But jesus those pistons have seen some detonation

Judging by the erosion of the lettering on one of the pistons? Or just the black sooty look in general.

 

[6A13TT TYPE S]

Ahh is that just carbon buildup. From.the photos is looks like pitting.

 

[Grid]

my homegrown tune was/is pig rich, just like the factory wanted it

 

[jungle]

I agree, bores look normal, just usual thrust wear

 

[Grid]

Cheers guys. After taking engine apart further pistons seem fine, only a bit of visible wear on the main bearings. Will be looking at getting them replaced.

 

[Grid]

Sooo engine got taken apart for inspection. All seems fine apart from tired crankshaft and connrod bearings. How to decode these markings? The fitment would be the second to last character (2's in this case)?

 

[6A13TT TYPE S]

No the bearing marks are ink printed onto the back shell. Which are long worn off during operation.
You should measure bearing clearances with a micrometer. Or have a professional do it if you dont have the skills or equipment. factory marking are a terrible way of getting clearances correct

 

[Grid]

Made progress. Visited a machinist with the block and crankshaft. Took measurements which only resulted in more questions.

Crankshaft journal outside dia: 55.99, 55.99, 55.985, 55.99
Cylinder block bearing bore: 60.04, 60.04, 60.03, 60.04

Is it just me, or is that mismatched with the engine manual. If the cylinder block bearing bore was so out of tolerance how did the engine even survive that long? We seated, torqued, degreased, reseated and re-torqued the bearing cap 3 times and measurements did not change. Arguably the manual is for the SOHC 6A13 and not for the DOHC variant we have. Machinist said it's not possible that the bearing bore got worn out of tolerance by so much because the surfaces looked mint.

What should I do now. Is there a different fitment table available somewhere? The journal bearings I removed from the engine still had their original ink stamped marks on: 2, 2, 3, 2. As you can see from the photo they were pretty tired.

As for the crankshaft pin outer diameter measurements, these seem normal:
50.992, 50.99, 50.984, 50.985, 50.985, 50.984

So it's only the cylinder block bearing bore that measures completely out of whack.

 

[6A13TT TYPE S]

I always order the bearing shells with the biggest OD and smallest ID. So grade 5. And then line hone (allign hone, line bore whatever you want to call it) the main tunnel to attain the bearing clearance you want.

If you buy bearings with a small OD and then hone the tunnel you can run out of bearing crush which makes them more prone to spinning. Although the differences between biggest and smallest bearing sizes is next to nothing.

Factory clearances are quite tight, i cant remember how tight off the top of my head but I always run them between 0.002" and 0.0025" (0.050mm - 0.063mm) clearance on both mains and big ends as the motors I build people are going to give them a hard time (track days/drags/agressive street etc) so a bit of extra clearance is beneficial

Keep in mind the looser your clearances the lower your operating oil pressure will be for the same oil viscosity and oil pump flow rate.

Same goes for conrods. Thickest bearings available (grade one in this case i think from memory) and then resize the rod tunnel. (Which will need to be done anyway if you put ARP bolts in as the extra clamp load of the ARP fasteners distort the tunnel out of round)

This is common practice and is the best way to attain the correct clearances. And this way you have all the same bearings and you know all your main tunnels and rod tunnels are identical in size.