Compression test

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Ltriumph
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Compression test

#1 Post by Ltriumph » Thu Jan 13, 2022 11:18 pm

I have a 1978 2000TC, had a compression test results as follows: 170, 150, 145, 145, 130, 150 - it does burn a little oil. I am not mechanically capable of pulling the head off etc, When I purchased it 5 years ago compressions were all within the 10% tolerance level, done about 15,000 km since. I do ant to keep this car for a long time. What course of action do you think I should take when discussing with a mechanic?
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Alec
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Re: Compression test

#2 Post by Alec » Fri Jan 14, 2022 10:08 am

Hello LTriumph,

the 170 is a bit odd, and the 130 a bit low. If you don't intend to keep it for long then the only thing I would do is to check the tappet clearances. This will affect the compression readings if they are not right, although by how much I don't know? If it's driving OK. then that is a factor as to what you do.

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Re: Compression test

#3 Post by Charles H » Fri Jan 14, 2022 4:29 pm

I will assume that you DO WANT to keep this car for a long time, therefore would firstly re-check no1 since it does seem a bit high compared to all the other cylinders. As before, check the valve clearances, and perhaps then check no5 with a little oil down the bore first to see if it is lower due to rings or a valve. Good luck.
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Re: Compression test

#4 Post by Ltriumph » Fri Jan 14, 2022 7:00 pm

Sorry about my computer skills. Yes I do want to keep it.
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Re: Compression test

#5 Post by Ltriumph » Fri Jan 14, 2022 7:02 pm

Meant to add. Lacks a bit of power on the hills now.
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Re: Compression test

#6 Post by Alec » Sat Jan 15, 2022 9:57 am

Hello LTriumph,

this is what I would do.
Go through setting the valve clearances, adjust the fuelling and ignition to the best they can be set and see if there is any difference.
I misread your original post, by the way, I didn't think then that you wanted to keep the car. The next step, if you are not happy with the running is to remove the cylinder head and do whatever is required to bring that up to scratch. This will also allow a view of the cylinders and give an idea of wear of the bores and pistons.

It may be that after removing and assessing the head and bores that it needs a rebuild with the option of finding a known good replacement engine, although Iimagine they will be thin on the ground. Personally I prefer to repair what I have and then I know it is right. With the best will in the world you do not usually know exctly how good a replacement engine is until it's fitted.

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Re: Compression test

#7 Post by Clifford Pope » Sat Jan 22, 2022 11:45 am

You do not mention whether those readings are with the wet test or the dry. Both are vital for diagnosis. I assume you have followed the basics:
Plugs out, throttle held wide open,insert gauge firmly in No 1, spin for 10 seconds. Repeat on the other cylinders.
Then do the whole test again, but put a teaspoon of oil down each bore.
The oil will largely seal the bores, so any improvements indicate bore wear, but repeated low readings indicate valve leakage, not bore wear.

Obviously the results will not be accurate if the battery is getting weaker during this process.

It might be worth injecting light oil or whatever is recommended for freeing sticking piston rings, and giving the engine a good hard run, just in case.

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Re: Compression test

#8 Post by Ltriumph » Sun Jan 30, 2022 8:17 pm

Thanks for your input. I had an engine reconditioner test it. The compression were around 120, went up by 15 with oil so rings on the way out. What I don’t understand is he did a leakage test. He said it was -5 but when he took the hose off between the tapper cover and carburettors it went to 0. He made a suggestion to close the carburettor inlets and put a bottle from the cover. I haven’t spoken to the mechanic yet. His suggestion is because I only do about 2000km a year, run it for a while ($8000 plus fitting for a recon). Would appreciate some knowledgeable feedback as you can see I’m not that mechanically minded - just a massive Triumph 2000 fan!
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Re: Compression test

#9 Post by Alec » Tue Feb 01, 2022 1:03 pm

Hello LTriumph,

the leakage test result seems peculiar? Did he do all six cylinders -5 (of 100 psi is the usual) is good, taking the breather hose of can't make any differnce Possibly the engine moved under the air pressure so losing compression on that cylinder. To do the test the cylinder in question is brought up to TDC on the compression stoke and needs to be held there as it's quite easy for teh air pressure to turn the engine. Once a valave opens you get no pressure build up in that cyclinder..
If you enjoy using it is as it is I would continue to do so, for a while at least.

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