Well, another exciting day: I was out driving and there was some sort of debris on the highway. Heard a little “clunk” as I wasn’t able to miss it. Stopped and checked the tires, all good. Drove on. What I didn’t notice was that whatever it was hit the grill and then the radiator, which was now slowly leaking all of its fluid. Or, rather, I didn’t notice until a grey plume of smoke came shooting out my engine some 30 min later, letting me know that I should have paid better attention to the temperature gauge.
I have 30 lbs of compression across all cylinders, and assume that I’ve burned the rings, if not worse.
So I guess we’re up for an engine rebuild!
I’ll start with: I haven’t rebuilt an engine before, but this seems as good a time as any. I guess we start with the extraction. Tips and tricks for getting the motor/trans out of an xk120 fhc?
Using aircraft engines as a basis, just because the compressions are low, one would not do an engine rebuild till the engine was borescoped. Will be interesting to hear the recommendations of Jag engine gurus.
Here’s what I know: I know that the engine got very, very hot, but was running when I shut it down. It turns over freely now, but won’t catch. I’ve tested and have spark at each plug and fuel in the system.
I did a compression test a few months ago and got: 1-185/ 2-175/ 3-190/ 4-170/ 5-175/ 6-175
When I did a compression test yesterday, they were 1-30/2-25/3-30 (and I stopped there). I was using one of those gauges you screw on to where the plugs go.
I don’t know how to test if the leak is the rings v valves v head gasket.
What would the next diagnostic step be?
I can get a borescope off amazon and take a looksy (post pictures here, because I wouldn’t really know what I’m looking for).
Pull the plugs, clean, regap. Not too sure what you mean by “fuel in the system.” Does that mean is going to carbs or just you know is in tank? Check that the three things fire, fuel, and air are available to engine. Sounds very basic and my apologies, but these early steps are a lot easier to do than pulling an engine. That the engine turns over is encouraging.
I did a compression test a few months ago and got: 1-185/ 2-175/ 3-190/ 4-170/ 5-175/ 6-175
Ben was this test done before or after the overheating episode? If before and now after the overheating you have low compression (30,25,30 etc. you should have checked them all while you were at it) you have ruined the rings. Hopefully you have not scored pistons and cylinder walls or cracked the cylinder head. At this point I would remove the head and have it checked for warpage and cracks. You will also be able to inspect the cylinder walls to check for any vertical scoring. If the compression test a few months ago was “before” those numbers indicate your valves and rings were in pretty good shape. You mentioned “no bank account”, if you are interested in just getting the car back on the road and the cylinder walls and pistons are OK this can be done in the car. This is something that I’m sure some contributors to this forum including myself have done many times in the past. Rings, rod bearings & valve job (the latter possibly not necessary in your case unless the head is cracked). This would be the minimum $ investment to get it useable again. Regards, Jim
Yes, the first set of numbers were before. (I can check the other three. It was just clear that I’d lost compression across the engine, so I assumed I’d burned the rings.)
I’ve got a $10 borescope coming from Amazon today, so I’ll have a look.
After that, it sounds like the next step is to pull the head, and that’ll answer a lot of the next questions.
As far as getting her back on the road: yes, that’s the goal. She is my (more or less) daily driver, so the goal is to do what’s necessary for her short and long term health, without wanting to spend a small fortune.
The block and head are original to the vehicle, so I’ll do what I can to salvage them.
First things first. You need to check into prices on machine work and parts. The old days are over, and it has become prohibitive to consider a rebuild. If you can live with non-originality, you may want to consider buying an XJ6 that still starts and runs and use its engine for your car. There are some bits that need changing, but you will be ahead in the long run.
I know some on here will cringe on that recommendation, but the engines are almost bulletproof if cared for, and an old, neglected XJ6 can be had for next to nothing.
If you have never done this before, I strongly, as in very strongly, recommend you get a factory workshop manual. It’s not complicated, but if you do something wrong, you can end up really costing yourself a lot of money.
Coolant in the cylinders, hopefully head gasket rather than cracked head. Was the grey plume of smoke from the exhaust rather than from under the hood? Paul’s advice very important. Mark position and remove hood (bonnet) for much easier access. Head will require vertical space due to studs rather than head bolts. Removing manifolds will make it much easier to handle. Cometic gaskets for every place they are available they are more expensive but well worth it for assembly. Hope it works out well.
You can’t magnaflux aluminum, that process is only for ferrous metals. There are penetrating dyes available for aluminum. Did you check the compression on all cylinders before you disassembled it?
If all cylinders were reporting around 25-30 psi then it is highly likely the rings lost their temper due to the heat. Based on the photos there was definitely coolant in the cylinders so a leak down test would have not been conclusive as to where the pressure loss was occurring.
If you want to test your rings without a teardown check to see if the head is warped by using a straight edge the full length of the head and across. If the head is not warped buy two head gaskets. Use one for remounting the head on the block and doing a dry and wet compression test. The other will be used only if the test fails and you need to delve deeper into the block. My experience has been that the head gasket blows and no major damage is done to the pistons and rings.
