[engine_work] Xu9j4 Mi-16 Rebuild

[kyepan 291]

This evening I bought a metal ruler from Halfrauds and realised that it was not accurate enough to measure liner protruderance, to my complete and utter shock and horror.

 

Checking against the block I thought there was a bow in the middle...of 0.06mm however, I checked it against the head, which has been freshly skimmed flat, and it shows the same bow no matter where you hold it... Sigh... should have known better, did know better... Still wasted £2.50

 

I've now bought a proper straight edge. for £20 inc carriage, and am waiting for it to be delivered.

 

The other thing I did was to finish cleaning the last piston and removing the rings, they all now weigh exactly the same according to my scales, granted the scales are only accurate to a gram, but they all read 1206g. mild win in the face of thinking i may have to get the block decked.

 

 

Secondly, i am still a little confused over the markings on the pistons, according to the rebuild manual

a- piston grade identification

b- engine type identification - either z for xu9j4 or x for xu9j4z... stupid lettering.

 

 

 

anyway, my pistons have some markings, but not something i can make sense of, so i present to you the following images

 

 

Cheers

J

Edited September 7, 2011 by kyepan

[kyepan 291]

82.97 makes sense as far as size is concerned, but if i'm on new liners, the clearance is going to be tight.....

[Paul_13 212 1 Cars]

Bloody Halfords ruler, no wonder there appeared to be a bow in the block

[Anthony 1,000]

Don't remember ever seeing pistons like that in any of the Mi16's that I've stripped or built - I wonder if they're pattern replacements or similar?

 

 

That's what the OE ones that I've seen look like, together with the markings as described in the build manual - as you see in the picture, that's a "B" sized piston from an D6C (XU9J4) engine (Z marked)

[kyepan 291]

Hi Anthony,

 

thanks for the reply.

 

Just out of interest, what are the B and C sizes? i'm guessing +0.03 and +0.06?

 

cheers J

[Anthony 1,000]

I don't have it to hand, but the size variation between A, B, and C marked pistons are listed in the Mi16 rebuild manual from memory

[kyepan 291]

firstly PDC appears to be a chinese manufacturer of aftermarket pistons..

look at the xu5jp section

 

This evening i have been learning how to measure things, i've done all the old liners along and across the thrust faces at three heights which vary by 0.03mm between 83.01-83.04 and the new liners which of course don't vary down the bore. and are 83.01mm as far as my measuring reference is accurate.

 

whats confusing me... more so as i finssh this bottle of red wine.. the piston i measured is a max of 82.94mm.. and i've spend about ten minutes just moving back and forth over it height and otherwise getting a good central measurement, it peaks perhaps 8mm from the bottom of the skirt.

 

I'm not asking anyone to tell me how to use a micrometer, but that piston seems quite small compared to the book quoted figures for the three sizes of pistons.

 

A - 82.963-82.977

B - 82.973-82.987

C - 82.983-82.997

 

Now it's not forged, which might explain the clearance difference, because i can clearly see the steel ring in the skirt (to thermally stabilise it) so it's definitely cast.

 

The relative clearance according to the workshop manual should be 0.035 according to the manual but i've got 0.07

 

i double checked by zeroing my bore gauge on the micrometer set to the piston size of 82.94, and it showed +0.07mm max deflection.

 

so... someone help explain the clearance issue.

 

also, my american small block manual says there can be from 0.0015 up to 0.015 inch for fancy pistons.. which is anywhere from 0.038mm to 0.381mm so my piston is.. double the clearance for standard pistons, but 5 x less than forged pistons, which we all know are less thermally stable and expand more.

Edited September 8, 2011 by kyepan

[kyepan 291]

so we're back to 0.07 being ok according to fours-stroke performance book

 

and this one

 

 

 

0.002 inches = 0.0508 millimetres

0.003 inches = 0.0762 millimetres

 

<iframe frameborder="0" scrolling="no" style="border:0px" src="http://books.google.com/books?id=OTOYHRSX_XcC&lpg=PP1&dq=four%20stroke&pg=PA239&output=embed" width=500 height=500></iframe>

Edited September 10, 2011 by kyepan

[petert 550]

0.07mm is a pretty wide clearance for one of those pistons. They aren't cast hypereutectic or forged. As you can see they have steel struts so their size will not vary very much with heat. There's no problem running that much clearance for a track car, but for a street car there will be lots of blow by caused by the increased ring gap. Run the breather hose into a catch tank rather than back into the inlet tract.

[kyepan 291]

Thanks peter, one question on your reply, how does piston to bore clearance affect ring gap? surely you gap the rings to the bore, so it's independent?!

 

Also i did some more measuring, this time with less wine, it's interesting to note that the new liners are not round. They are brand new and manufactured by Kolbenschmidt.

 

Piston measurements

1) 82.96mm

2) 82.96mm

3) 82.955mm

4) 82.95mm

 

Bore measurements on the new liners, Bore gauge zeroed to 83mm on same micrometer used for pistons

 

Thrust face on new liners

1) 83.008mm

2) 83.002mm

3) 83.013mm

4) 83.005mm

 

 

perpendicular to thrust face....which makes sense because of the piston cam grind.

1) 83.001mm

2) 82.995mm

3) 82.990mm

4) 82.990mm

 

smallest piston with smallest liner then upwards towards the larger ones

Piston 4 82.950mm liner 2 83.002mm = 0.052mm

Piston 3 82.955mm liner 4 83.005mm = 0.050mm

Piston 1 82.960mm liner 1 83.008mm = 0.048mm

Piston 2 82.960mm liner 3 83.013mm = 0.053mm

 

took time cleaning contact points and zeroing the bore gauge every time, i re-zeroed liner 3 after it measured 83.012, but it still came back as that... so it's just bigger.

 

Max clearance is 0.0020 inches

Min clearance is 0.0180 inches.

 

Much happier with that.

 

Cheers

J

[petert 550]

It depends where the rings come from. Replacements are usually pre-gapped, so bozzo mechanics can throw them in. Rings supplied with new pistons require gapping. Just remember an increase of 1 thou on the diameter is 3 thou on the ring gap. (P=pi x d).

[kyepan 291]

Replacements are usually pre-gapped,

This is what i have also read, hopefully with the new liners they won't be too wide.

 

Just remember an increase of 1 thou on the diameter is 3 thou on the ring gap. (P=pi x d).

i'll check each ring and see if there is any variation, if so i'll match the tighter ones with the bigger liners.

 

cheers

 

J

[wicked 103 3 Cars]

@petert: currently I'm also rebuilding my Mi16 and wonder if you've also ball park figures for the ring gap?

[kyepan 291]

@petert: currently I'm also rebuilding my Mi16 and wonder if you've also ball park figures for the ring gap?

it doesn't give a gap in the official xu9j4 workshop manual because replacement rings come pre gapped for normal road use.

 

Unless they are special (moly / chrome / ceramic coated) rings, for special pistons, in which case the gap is down to they type of ring, and type of use / amount of heat that the engine is going to see.

 

so there is no standard answer, unless it's standard rings for road use.

 

haynes book of lies states

 

top ring

1905 cc engine . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 0.2 to 0.4 mm

second compression ring

1580 cc and 1905 cc engines . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 0.15 to 0.35 mm

oil control ring

All models . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 0.3 to 0.5 mm

Edited September 12, 2011 by kyepan

[wicked 103 3 Cars]

 

 

haynes book of lies states

 

 

The reason I'm asking peter...

[kyepan 291]

how wiesco say to do it.

[petert 550]

yep, as per that wiseco table. Note, the 2nd ring is always bigger.

Edited September 12, 2011 by petert

[kyepan 291]

So lets do some initial measuring of some rings, i'll be getting my better feeler gauges later on this week, but this should be indicative.

 

Simply according to the above table, because the ring manufacturer doesn't seem to have any on their site.

 

83 * 0.005 = 0.415 mm ideal ring gap

 

I have 0.38 mm.. with my crappy feeler gauges.

 

so that's pretty much bang on

 

Have been doing some more reading on NPR rings, and they seem quite reputable, they even have individual security tear offs to check they are genuine product, which mine are..They are also PVD, unlike the sharp edged iron top that was removed.

 

Many years ago Nippon Piston Ring started developing wear-resistant PVD coatings. PVD stands for “physical vapour deposition”, a vacuum-based coating process where layers of hardening components are directly deposited onto the surface of the piston ring. The PVD coatings are notable because of their high wear-resistance. This is achieved by a high hardness (1400-2200 Hv) and an extremely compact layer structure. A further advantage is the very smooth surface which results in considerable friction benefits.

PVD technology is increasingly being used in conventional petrol engines. Its high wear resistance maintains the ring shape over a longer period of time. For instance this allows a reduction of the ring tension of PVD coated oil control rings which in turn results in considerable friction benefits.

 

So new bores, new rings that the part numbers check out on, and some fancy coating on the top compression ring, winner.

I also read this. clicky which is interesting.

Edited September 12, 2011 by kyepan

[kyepan 291]

just a quick post, although i'm going to post up exact measurements when the straight edge and decent feelers arrive.

 

Last night the other thing i did was spend some time putting the liners in (without seals) to check roughly what kind of protrusion i had.

 

Very little seems to be the answer, except on the last cylinder (cam end) which seems to stand up noticably on one side (cam end), it also rocks, and has much more interference when seating it. I put some blue on it to try and see if there were noticable high spots but it would seem either i didn't apply the blue properly or the light wasn't good enough

 

I've read that these blocks warp significantly.. so i'm going to measure accurately, but a quick question.

 

If the seats are... not flat, what are my options?

 

Cheers

 

J

[petert 550]

The seats tend to sink on one side. So ideally you need to machine the liners so they sit square with the deck. It's a messy business to get right. Then the liners will go in one way only. The alternative is to recut the liner seats perpendicular again and recut the deck to match. Again, messy business which ever way you look at it and you'll need a competent machine shop.

[Sandy 189]

Very competent one that fully understands the scenario! I find if you clamp the block down flat on a bed, the error is usually mostly seat cleanliness. A good firm scrape and wire brush will usually sort it. The block distortion tends to be around the head bolt holes and a decent surface grind will all but eliminate it, while remaining inside tolerance for protrusion.

 

All hail the EW!

[kyepan 291]

last night i started measuring the old and new liners, and comparing protrusion, first results are interesting, will put up more tonight when i have measured all of them.

 

cheers

J

[kyepan 291]

a quick update, received my straight edge, feeler gauges and piston ring pliers.

Not much progress, as i was racing and fighting this weekend,

 

Except to say that the liners are now sitting properly, the new liners had small raised bits along the edges of the seat where it they are cut flat, so i radiused them very gently and they no longer rock in their seats and all sit within tolerance.

 

 

I'm still chasing some bits of the deck, around the oil returns from the head where i'm getting little or no protrusion.. i'll put up a chart.

 

I also enquired about machining both, the place i spoke to HT howarth in slough, he's about to receive a new boring and facing all in one machine. He said he would do the seats and the deck at the same time, with the same machine to get it accurate. However, it will cost 120 plus vat, and i only have a few high spots on the deck, and the minimum he could take off the deck is 0.03thou which i just don't need.

 

Anyway, i may look at the deck again with some thing flat and some wet and dry just to knock off the high spots.

 

J

[kyepan 291]

just a quick update, I'm still not happy because there is just not enough protrusion in some places, and the bare minimum most everywhere else, and cleaning further is only going to reduce that.

 

Am going to get the seats recut, and the block decked, yes it's money, but i also think do it right, do it once.

Edited September 22, 2011 by kyepan

[wicked 103 3 Cars]

What's the protrusion you aim at?

I did some quick measurments on my engine and they were also within 0.03-0.06, which is just good enough according to the rebuild manual.