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Absolutely no compression

T

Toora Stephen

Member
Hi all,
I replaced the head gasket on the weekend. After I put everything back together again, it wouldn't start (1951 TED20). It sounded like it was firing on one cylinder. In fact, it did start a couple of times but of course couldn't keep running on only 1.

I have a new compression tester, so I tried that. On cylinders 1, 2 and 4 there was absolutely no compression reading. Zero compression. On cylinder 3 I got about 90 which was what I was expecting.

How can there be no compression? The pistons looked OK to me. I didn't have a close look at the valves, but I didn't notice anything unusual. Could it be that the valves are not closing properly? Wouldn't you still get *some* compression??!

Any ideas? Where should I start?

- TS
 
Do you think the timing gear/ chain is broke? #3's valves are closed, everyone elses valves are open at least a little. good luck!
 
If you have zero compression on 1,2,& 4, then it's most likely a valve(s) is not closing on those cylinders. Are you sure you got the pushrods on the tappets and on the rockers when you put it together? Are the adjusting screws for the valves screwed all the way down so the valves aren't closing? Did you do anything to the camshaft/timing gear/timing chain when you took the head off?
 
Did you set the valves again after finishing torqueing the head bolts? If that new gasket was thinner than the old one, the valves would be held open.

Gerald J.
 
I'm pretty sure I aligned the rockers with the rods and tappets, and screwed them down.

I may need to set the valves - I just assumed they would be OK.

Thanks for the replies. Hopefully one of the above 2 issues is all it is... :)

- TS
 
Toora Stephen
Properly setting the valve lash is critical.
Check clearances again after it is at operating temperature.
Brian
 
The valve clearance is very dependent on the head gasket thickness. You absolutely HAVE to set the valves after changing the head gasket, there is only one other option and that you already have, an engine that won't run.

Gerald J.
 
I would also check valve lash after head has been removed. I believe inlet should be 0.010" and exhaust 0.012. You could check this at TDC no.1 cyl on compression stroke which would be bothpush rods retracted into block and no. 4 in rock position( one valve closing and the other about to open.) then follow firing order 1342 every 1/2 crankshaft turn in normal engine rotation.
 
You cannot expect the valve clearance to be correct if you have removed the Head, you must reset the clearance, allow the engine to get to working temperature and then tighten the Head Down again and then reset the valve clearances again, you may have to reset the valves a couple of times to get them correct, especially if there is wear on the valves and rockers. If set correctly and no wear there should be no noise from the valve gear, they run very quiet, but often the ends of the valves wear and the face of the Rockers that rubs on the top of the valves wears a hole in the machined face of the Rockers.

John
 
Thanks again for all the replies. I have to say I missed the bit in the manual about adjusting valve clearance when I replaced the head gasket. The first time I replaced it it didn't seem to matter! I guess I was just lucky that time.

This weekend I will get back in there and adjust the valves. Do I need any special tools?

- TS
 
Thanks, that's pretty-well what I expected. I also have the procedural advice provided by John (UK) and recently posted by motorv8n, so I should have no problems! I'll let you know how it goes.

- TS
 
Hi all,
I adjusted the valve rocker gaps and reassembled. The tractor started up right away and ran fine... at least until I got stuck. I'll post about that later.

Thanks for all your help.

- TS
 
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