TD piston replacement

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TD piston replacement

Post by tedjan » Wed Oct 16, 2019 11:10 am

Hello Again,
I am working on a 54 TF that has a TD engine that smokes blue from the exhaust due to worn rings.
Compression is as follows:Cyl.1-100 lbs,Cyl.2-125 lbs,cyl.3-125 lbs.and Cyl.4-125 lbs.Upon a wet test,all cylinders read 150 lbs.
I am going to replace the rings,assuming cylinders are ok.
According to the manual,pistons come out through the bottom and head does not have to be removed.
Upon refitting,will I need a special ring compressor?as the manual does not provide info on this step.If so,where can I buy one?
Thank you.

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Steve Simmons
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Re: TD piston replacement

Post by Steve Simmons » Wed Oct 16, 2019 11:18 am

Personally I would not only remove the head, but use this opportunity to do a valve job to get the most out of the new rings. It also makes it a lot easier to check rung gap at the top of the bore. Be sure to check the ring grooves in the pistons for wear while they are out. Check at the inside edge of the groove because this area wears more than the outside edge. A ring compressor is a good idea to protect the rings as you insert them. They are available at most auto parts stores or online parts suppliers.
1949 TC8975 / XPAG 9609
1949 TC9849 EXU / XPAG 10507

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Re: TD piston replacement

Post by EdCallo » Thu Oct 17, 2019 3:58 am

The pistons need to go in through the bottom as the big end of the rod will not fit in the cylinder bore. As above, remove the head so you could at least give the bores a quick hone for the new rings. What I have done is put the pistons in through the bottom, pushed them part out the top, put the rings on and then pushed the piston back into the bore. Now if you have 4 ring pistons the bottom ring still has to be installed from below. I have used the band type you tighten with a wrench for this.

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Re: TD piston replacement

Post by tedjan » Thu Oct 17, 2019 1:43 pm

Great advice.Thank you very much.
It always amazes me when a job description is different(e.g.pistons removed from the bottom)from other cars,the workshop manual neglects to tell you how it's done.
Take care.

Tom Lange, MGT Repair
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Joined: Mon Jan 07, 2013 10:14 am

Re: TD piston replacement

Post by Tom Lange, MGT Repair » Thu Oct 17, 2019 2:21 pm

I hate to tell you, but you are really just putting a band-aid on your engine by JUST doing rings. If you have bad rings (and your readings do indicate that - I am suspicious of anything below 145# dry), there are so many potential engine weaknesses associated with your cylinder wear. The rings are bad for a reason - is the bore also tapered? Is there a ridge at the top of the cylinder? These all need looking-into.

You can fix one problem (the rings), but there are so many associated parts that still may be weak. As noted above: the head - what of the valve seals and guides? A quick lapping-in of valves (or valve job if necessary) will go a long way.

But you don't mention bearings, main or rods. If the engine sat for a time, the bearings will show acid-tracks from the old oil, and should be replaced. And what about the oil pump? What about the cam and followers? Timing chain and gears? Brass core plugs? And if you have it apart, have it balanced!

I realize that this is creeping - one thing really leads to another: the hip bone is connected to the knee bone, the knee bone is connected to the shin bone, etc. But if you want an engine that will last, do it right, and look at the larger picture. If someone came into my shop and wanted JUST rings, I would look at all those other parts whether he asked me to or not, and I bet I would find things that would compromise his engine in a matter of perhaps ten thousand miles. If you just do rings you are doubling or tripling stress on the bottom end, for instance.

By the way, I have had total satisfaction with Deves rings, much better than the usual Hastings which did not seat in two engines I did. I now only use Deves.

Tom Lange
MGT Repair

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