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- #181
Yeah it's been pretty annoying. I've chased down dozens of rattles thinking I'd found it, then on the way to work it's there again.I've had some weird noises on my little diesel over the years. More than a few had a tinny rattle sound to them. Just a few ideas to throw out there: Make sure to check your crank pulley, as they can start coming apart at the rubber (mine did). Another is, sometimes people don't torque the crank pulley bolt enough, which can allow the crank pulley to damage the key way over time leading to weird noises (I haven't had this issue, but have seen it plague more than a few). Of course there are tensioner and accessory bearings which can make misleading sounds sometimes. I've even had the v-belts themselves make some very strange noises at a certain age even with proper tension. You've probably checked all that...but just some suggestions.
Your compression numbers sound pretty good. As you know, a big indication of diesel compression is how well cold starts go. Easy starts indicate things are probably pretty good. And of course oil usage and blow by. Have you tried that oil cap 'tea pot' test?
Does the 12HT feed the crank case ventilation into the intake (pre-turbo)? That can sometimes cause lower compression numbers on the middle cylinders that take the bulk of that oil mist coming out of the cross-over pipe to intake manifold. Not so much from damage, but I think crud builds up on the back of the valves/seats and they don't seal as well over time.
On the topic of crank case ventilation, is it still hooked up pre turbo (assuming 12ht came with this)? That could be the source of the oil in your turbo (if its on the compressor side). It really does make a big mess. And gets worse if you have above average blow-by.
Pulling your motor apart is probably a good idea in any case. Especially as you've been able to collect the parts already. My bet is your pistons will be a little worn, but not too bad yet. I bet the cylinder bores will be fine to take your new pistons.
Main trick will be getting the new rings to seat right. All in a proper hone and break-in procedure I guess. I've seen so many DIY rebuilds where this seems to fail for people. Maybe they try their own hone job? I think I'd use a machine shop if I were to do it....
Anyhow, will be interesting to see how this goes. Once you get those new slugs in there you can confidently tune up for a bit more power too. Especially if you pop a new more efficient turbo on.
I think Jonathon was toying with doing some of this same work on his 12ht at some point also.
It's hard to get the noise to happen anywhere except the highway. So a quick burn down the back road doesn't even do it. Needs to be third gear or higher to get the right amount of load.
Even wondered if it was the waste gate, but it's really not tied to boost levels, near as I can tell. Happens anywhere from 2-14 psi, once I'm up to close to 2k rpm.
Only hearing it after the LHD swap had me thinking rattle, but could be just because there's so much less soundproofing on the older firewall.
From what I've read, all 12ht's got the same pistons, and even good ones have ring lands that are considerably wider than they started out...but I'll have to see when I get there. Mines in the 88-89 range somewhere, but they only made them for a few years.
I thought about doing a leak down to see if it was valves but if I'm taking it off anyway, meh. I'm sure they'll be gummy and nasty. Breather is vented to the intake, so yeah that's probably where most of the oily mess comes from.
I bought a catch can a year or two ago, just haven't gotten around to installing it.
My oil pan needs to come off for a good clean up and paint , so there's a few reasons I'll be in there.
I watched the old mechanic at the boat yard hone about a thousand little sailboat diesels, so I planned to give it a go myself, but again, have to see how it looks.
If it's really glazed or something I could see taking it to an expert, although I'm not really aiming for a full rebuild. That level of expense isn't really worth it to me.
More minimum amount of work to put new pistons in (if needed) and make sure something bad isn't about to happen.