Seized Navi

[Umbelina Baublitz]

Thereis a cylinder liner in the barrel but on the right side. No damage on this side. I had the barrels rehoned after the engine seized the first time. so there should have benn a bit more clearance.The piston size is now 63mm+ 0,10. There are no other oversized pistons available as far as I know. Except one +0.20 piston on Ebay.

Please check your ignition timing. The correct figure is 24 deg BTDC (Before Top Dead Centre) fully advanced. Check this with a strobe. You will see other figures quoted in various manuals BUT 24 deg is the correct value for a Navigator.

Make sure you find Top Dead Centre accurately - using a piston stopper. If you try to judge TDC by feel - you could be as much as 5deg out. The Navi (& its sisters Jubilee & Electra) have very short stroke engines and the timing has to be spot on!

I just completed the order of one new piston and rings form the NOC shop.I checked the timing and it is at 24 BTDC. We can use the same size piston . There are no mark in the cylinder, just aluminium sticking to it.

It is fairly common, after high mileage, for the sludge trap in the crankshaft to become so full of sludge that the left hand big end journal oil feeds get blocked. No oil is thrown onto the cylinder liner and the piston will seize.

Hello Ulrich, when you come to do this, I was amazed at how much hard sludge there was in the trap. I used a wire to chip it out, then pipe cleaners and parafin until there was no evidence of any sludge, I did have to take the crank out to do this though as I cleaned from the journals in. You may find your big end bearings are scored as well. Hope it wporks out for you.

I've done at least three different lightweight cranks. In all cases the aluminium cover screw on the end of the sludge trap refused to move with a broad screwdriver to the shallow slot. The slot is only of use to insert a new plug.

I drilled a 3mm hole through the centre of the plug. Then two more 3mm holes along the slot. The slot helps locate the drill. Then use a needle file to remove the bridge between the holes and insert a strong large flat bladed screwdriver. If is has a square shaft or a driving hole in the handle all the better. You may need a Mole-grip on the screwdriver shaft.

If that doesn't work, lengthen the slot until it is at the top of the threads, don't damage the threads of the crankshaft, and try again. Hopefully the cover screw will collapse inward a bit and lose it's grip on the crankshaft.

On a Jubilee, which has a smaller diameter screw cover to Nav/Electra, I had to resort to another pair of 3mm holes, like a number 5 on a dice, and make two slots, elongated to the threads. I was able to punch the four quarters of the mutilated screw inwards and to freedom.

Then I used the strong long screwdriver to chisel and remove the sludge. As Andrew says this will be compacted. Be brutal and ensure there are no pieces left inside. The sludge always collects more at the far end, the left end, where the oil flow is lowest.

If you have a parts washer, use it to thoroughly clean the oil passage from the timing side oil feed (end of crankshaft) to the sludge trap. Or an airline can be used. Bits of aluminium may have fallen in here from all the drilling and filing. A trick is to use a grease gun on the oil feed to fill the oil passage with grease before you start drilling the aluminium. Then, at the end, push in more grease to drive any swarf into the sludge trap where you can remove it. Then clean out the grease with paraffin and pipe cleaner. (or parts washer)

Need more pics to confirm, but seizing on the side with nodules on the piston top suggests a 4 cornered seizure from pre-ignition heating the piston. The 4 corners are the points where the piston is thickest and the more material the more expansion ie either side of the pin on both sides.

The crankshaft can now be removed. Sometimes the timing side bearing is tight on the crankshaft. Don't damage the timing side end detail on the crankshaft by hammering. This is important for a good oil feed seal. Use a tube to push on the shoulder at the top of the left hand thread if necessary.

Today I borrowed the three jar puller for the crankshaft half time pinion and took the engine apart. I left the camshafts in but noticed excessive play in the timing side bushes so the had to come out also.The nuts were very tight but in the end they loosened up and I could pull the pinions.

The piston failure is not down to a blocked crank then, So some more carefull detective work is needed. What piston/bore clearance have you been using.?., If your engineer is a car guy he may be not familliar with aircooled motors.

hello now everyone as gone thought everything they can think of that the cause of this unfortunate incident but as any of you come across the oil strainer filter in the sump plate As I have been dismantling my 350 Navigator I found the sump strainer filter to be partially blocked by red Hermerite gasket sealer on further inspection, I find a layer of thick oily gunge that was also blocking the oilways you should check this part of the sump plate is clean If the oil pump cannot pick up oil you get a seizure somewhere, yours anna j

Very common for particles in the oil, like carbon, to seep between the close fitting piston and bore of the relief valve. The piston jams in the bore and is not pushed back onto the seat by the spring. Oil then spills continuously from the high pressure oil supply before it gets to the crankshaft. Of the handful of pressure relief valves I inherited, the MAJORITY were in this condition. It's easy to check the valve is clean and piston free by separating the valve body halves.

Also a new crankcase vent tube with a bigger diameter was installed. Some PO drilled in a bolt with a 3mm hole in it. I will fit a small breather valve so that air can get out of the crankcase but not in!

I got my camshaft and other bushes from Russel Motors. Very reasonably priced but I had to keep calling until someone took my order. I had to wait a while until he was "Going to the warehouse across town" to find out if they could supply them. Worth the wait though.

Hi Navigators: I have already posted this on the forum, but your correspondence here seems closer to the mark. My Navigator pistons are in an engineering shop, and he wants to know what the maximum and minimum gap tolerance is between the barrels and pistons. Mine are 40 thou oversize. He is concerned there may be too big a gap there

Although Ulrich has been asked several times what clearance his engine has been set up with,he has declined to answer. I can only assume he does not know. He needs to ask his engineer if he can't measure it for himself. With this information members can give him the benefit of their experience which may stop him (and possibly his engineer ) making the same mistake a third time.

I have to ask the man from the engine shop for the clearance. When I got the barrels and pistons he bored it out for a clearance of 10 thou. After the first seizure it was 20 thou and now I guess 30 thou after the third honing.

Hi Ulrich, 10,20 and 30 thou are the oversize of the pistons. What we are interested in is the final clearance between the piston skirts and the finished bore. This varies with the manufacturer of the pistons and the material the pistons are made of. Air cooled engines usually need more clearance than watercooled and some engines need a bit more clearance than expected due to poor lubrication or heat distorsion. or poor engine orriginal machining. There will be members here who have lots of experience with these engines and may be able to advise on what they have found to work. Its also very possible that your problem is down to overheating on that cylinder and your clearances may be ok,but it would help to know as much as possible .

Hepolite service manual 1961 gives lots of information about pistons and clearances and where to measure and how. Fascinating that pistons at room temperature are oval becoming round at running temperature. Skirt dimensions vary from bottom of skirt to top of skirt . All information is general and needs careful reading to help decide whats best.

I have no data or insight into Navigators, but as no one is posting to advise Ulrich I would suggest that the clearance on the thrust face just below the bottom rings should be not less than three and a half thou. Any better offers?

Looks about right to me according to the data posted by Graham. If that's what it was, maybe add another 0.01"? Or two? The catalogue confirms that the piston should fit correctly if the over bore is correct, so the correction ought to be made in the piston. I don't suppose the machinist added 0.02mm instead of 0.02 inches (0.58mm)?? Then run in very gently to begin with. In olden days they might take the block off after the first hundred miles or so and file away any signs of hard polished marks! Allegedly.

Following these threads from the very beginning I've wondered throughout whether the whole thing has been as a result of incorrect running in but assumed that it couldn't possibly be so. I do find myself wondering however about riding a newly-rebored and re-pistoned old 350 at 60 (mph? kph?). Stranger things have happened..

Hi David, If Ulrich gets another 0.01" clearance added it will sound like my 99 !!. I think you meant 0.001 thou. IE one thou. When I had my 99 bored to plus 10 thou the engineer advised me that with 31/2 thou clearance there would still be some wear shadows on the bore. I opted for an extra thou ,IE 41/2 thou and put up with a little noise when cold. Sounds just like an old Brit should. I recently managed to properly overheat my motor with bad carburation but no lasting effects .There are now coatings that can be applied to piston skirts that wear away to give close clearances and quiet running, would like to try that. I would prefer a quiet engine ,but knowing that sooner or later I will "F" up somewhere ,a safety margin helps. Its also possible that the fully synth oil I am running helped to protect the motor.

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