Oil leak from a through bolt.

[Clive]

Hi folks, it’s been a while since I had a Jab problem but I find myself with a pesky oil leak from one maybe two through bolts.
The cause I believe is break through from the oil gallery adjacent to the associated through bolt.
Now when I replaced the through bolts after a breakage a few years ago I found one gooped up with silicone sealant.
I though ah, here we are, this engine must have has a through bolt leak in the past. I’ve always had the engine and knowing it’s history the goop must have been put on either by our friends in Bundaberg or by ST aviation at the 1000hr overhaul.
Any how, no matter who or when. I re gooped the new bolt in the previously gooped hole and all was well.
Recently though I have isolated the oil leakage to at least one of the bolts on the lower side of #3 cylinder.
Strangely the bolt that I seem to remember being the one that snapped.
This would fit with the theory of the use of engines in the training environment which is what promoted the broken bolt some years. Back when my son and son in law started to learn to fly in my (now our) aircraft.
My question is does anyone have any tips on gooping a through bolt?
I plan to do what I did last time which seemed to work as the previously gooped one hasn’t leaked.
I ask this as it a few years down the road now and maybe others have come across and fixed through bolt leaks?
BTW this is an early 2200 with 1700 hours in it. Treated with great TLC until flown under guidance from a flying instructor.
Thankfully it will now be flown once again with TLC as the licence has been received.
Regards to all, Clive

[diablo]

Hi Clive,

I presume that it is not one of the bolts that goes straight through the crankcase but one of the studs. It sounds like there is some sort of wear, warp or crack internally, possibly the thread that you found filled with silicone ... I really don't think it came out of the factory like that.

Cracks in places like that are unusual. Best to go back to basics which probably means a complete strip down and identification of root cause. Anything less, is just a patch on what seems to be a bigger issue. If it is a crack, a good engineering outfit will be able to stitch it and machine the mating surfaces to spec.

Happy to help out on the strip down and catch up. I also have a guide on stripping top and bottom half (in colour) if you need one.

[Pete Twissell]

During the recent strip of my 2200, I found that the cases had been fretting around one of the through stud bores adjacent to the centre main bearing. The stud had not been leaking, but was oily.
The implication is that the stud had not been sufficiently preloaded (torqued) to keep the cases together under running loads.
This is one possible cause of an oil leak through the stud.

[Clive]

Sorry I never came back, I don't get notifications from this forum, I'll have a look and see if I can turn them on.

Thanks for the comments:
Leak was from a through bolt, not a stud. From the bolt that snapped 3 or 4 years ago, rear lower on #3 next to the fuel pump. A new set were fitted after that and that was when I found the siliconed bolt, the back lower on #1. Unlike Dean I think it was most likely from new as the 1000hr rebuild was unlikely to have involved the through bolts. I won't say what my thoughts are about a new engine with a siliconed through bolt, 20 years go though......

Anyhow, I have now tried everything I can, gooping the through bolt, O ring and goop, finally a sized O in a recess. Unfortunately as I think there is full 75 psi pressure on the bolt cavity nothing is fixing it. The aircraft has been used to train my son up to his licence and the practice of climb and decend, power and idle, promoted the snap and I believe the subsequent leakage. Upshot is I'll have the engine out shortly and split the cases for an inspection. What we find will decide the way forward. I'm hoping to get some Camit thru bolts. The engine is at 1730 hrs so maybe time to do a full rebuild though I changed the valves recently and everything looks good apart from burning a bit of oil (it always has) she's running lovely.

Reviewing my pictures of my 3300 when it was split there looks to be a drain channel machined from the through bolt cavity down onto the sump? I don't think the early engines have this so I'll add it.

It's a shame this has developed and my son has his licence and has moved away and he was talking the aircraft with him to build his experience and hours, also to burn off the last 270 hrs before we do the full rebuild. I do count myself as fairly lucky as this early engine has largely been trouble free for me, well in comparison to others I've read about and mer over the years. Hopefully I'll have a positive update in a short time.

[diablo]

Clive,

Your engine has definitely been one of the most reliable ever and shows that regular maintenance carried out by a knowledgeable and competent pilot pays dividends. Saying that, there are engines out there with over 4000 hours!

Evidence of a leak on through bolt implies that the crankcase halves are leaking maybe due fretting or some sort of old imperfection. I suppose the first question i would be asking is if the fretting or imperfection has caused some wearing away of aly. Hence, sealing will not be as good as it should be. Regardless of what you gunk it up with, it will only temporarily hold. The only real solution would be as follows:

1. complete strip down
2. thorough check of crankshaft (run out within spec if it is not, a regrind)
3. Check crankcase surfaces and regrind so a they are true
4. Line bore crankcase (oversize if crank has been reground)
5. Match and fit oversize bearings and re-assemble ensuring you dont skimp on essential bits like through bolts!

It should last you another 2000 hours without probs ...

happy flying

[Clive]

Hi Dean, I plan to follow your list but I hope not all of it!
Don't see why the crank should be out of spec but one never knows....
7/16" through bolts for sure if I can get them though I don't know if they will mean removing material near the current failed channel.
Not sure if that's a great idea though the extra clamping force will be a good thing.
Will report back.

Regards, Clive

[Clive]

The engine is almost back together. Alas I didn't find the cause of the leak so it could have been a few things or a combination.

Anyhow, Kevin up at Beverly was star and fitted me in urgently to fettle the barrels, open up the cases for bigger bolts and also had the parts I needed. Will still need pistons and barrels eventually but I will wait till Kevin has these available. He has a neat operation at Beverly, lots of machines and a rack of parts and second hand parts. He will be building up some engines when he gets time. very helpful and knowledgeable guy.

Hope to run it later this week!

Regards, Clive

[Clive]

Well I suppose I can excuse myself for not thinking of what the problem could have been.....seeing that the combined knowledge of all those that viewed my post didn't suggest an alternative cause of the oil leak.

Kevin blasted the barrels for me so they ended up in a fetching matt black as Chris, my son, painted them with Kevin's recommendation of MipaTherm, we teated my wife to a cake icing stand so we could rotate the barrels as they were sprayed. Ended up with a lovely job of 4 immaculate cylinders. Interestingly, when they were naked they were two different types. 2 of one type and two of another, physically the same but definitely manufactured differently.

Right back to the rebuild. I incorporated the recommended updates from the manual, fitted the spreader plate and Nordlocsand when all was done as much as I could in the workshop I got a couple of guys at the airfield to help me lift it on and I hooked it up, fitted the prop flange prop and then oil pump. Just about when all the work was done my son turned up with his usual slick timing. It was just getting dark and I tried to start it, no joy....figured I'd add a big battery to get it to crank faster, with the honing she was a little tight. Still nothing.....ah yes, fuel was turned off a couple of weeks ago when I started, that might help.
Alas after 5 minutes the oil was back, still coming out around the two lower thru bolts on #3. I was losing the will to live as we crouched in the dusk with phone lights shining trying to see what we could of the oil on our immaculate black barrels. My eyesight close up needs various magnification of glasses but the lad had no such problem and there was a shout of a eureka moment, party burning his nose on the exhaust and partly seeing the problem. What, look there, what? Photo taken and enlarged and there it was, a hairline crack about 2 inches long above the forward thru bolt.

At last! the thought of more work was dismissed as I now knew we would soon have it fixed. I got the plane back in my hangar about 3 months ago and the pesky leak that had first been nothing at all but I wanted Chris to take the plane away to its new base near his new home in Hampshire snag free. Little did I know it was going to take me so much time and so many visits to the hangar.

I thought I'd test my old friend and experienced Jab engineer out and sent him a simple text, 'it's still leaking, it's not the thru bolt but we know what it is, guess?'
Instant reply 'hairline crack' maybe I shouldn't have been so confident in saying I knew it was the through bolt.

Kevin continued with his 'stardom' and said he'd have a useable second hand barrel in the post by the end of the next day!
He was annoyed that he'd missed the crack, he said the honing normally shows any flaws up, but it was a very fine one and I'd had a good look and not noticed anything. The barrel still has a fairly nice ring to it.

Good excuse for a fly so I flew up to Beverly in the 9 and had a quick lunch with Kevin and was soon flying back to Norfolk with a nice example of an early Jab barrel in the back.
I had it on and ready to fly a few hours later and this morning we ran it up and all is good, as is the way the weather is now going to be rubbish for a long while so flying will have to wait. The Jab's trip down to Hampshire will be later in the month as it will need shaking down after sign off so it has a good few hours on it before Chris continues to build experience after gaining his licence in the summer.

Thanks to Kevin for all his help, his supply of all the seals, shells and the bolts, the fettling of the barrels and his advice, his suggestions and customer focus, also to Roger who talked the whole thing through with me at his sons Wings ceremony 10 days ago at RAF Shawbury (fantastic event, I was honoured to be invited). I stripped a 3300 in the past and Roger supervised the rebuild, that was 5 years ago so my memory of it was a little murky. And my son who was actually at the strip for part and also most of the rebuild. Also to Jabiru for what is actually quite a good manual, there are easier ways to do many things but it you follow it you won't go far wrong at all.

Crack picture available but how do I upload it?
Forward plan is to fit Camit style barrels and Mahler pistons when Kevin has them available sometime next year, that will complete the 2000 hr rebuild and the early solid with big heads should be good for another 2000 hrs.

Regards, Clive

[leslloyd]

Clive,down the bottom of reply go to "upload attachment","browse" and then select pictures then "add file",and you can add a comment to each picture.
colin

[Clive]

Thanks Colin pictures added