Woc123 Posted March 20, 2018 Report Share Posted March 20, 2018 I have a 1971 datsun 521 can anyone help me the compression test said its 105 for two of the cylinders and then 160 for one and the last one is 85. My mechanic thinks its the rings on the pistons thats messed up can anyone tell me if that is correct also if it is can we change the pistons out without removing the whole engine? Thanks Quote Link to comment
datzenmike Posted March 20, 2018 Report Share Posted March 20, 2018 Yeah those are low numbers alright. All at 160 would be better and higher, even better than that. There are several things that can cause low numbers... but if smoking as well, then I would say the engine needs to be rebuilt. You can, with much difficulty, work on it with the engine in place but.... This badly worn it may need to be over bored to the next larger size and larger pistons and rings installed. The cylinder diameters will need to be measured for this and the engine removed and taken apart and the block sent away for machining. You will need to source over size pistons and rings, an engine gasket set, new rod and main bearings and the head should be rebuilt or have the valve seals replaced at least If not too badly worn you can do a hone and ring job on it. This means removing the pistons and putting new rings on them and lightly honing the smooth cylinders so the new rings will 'wear in'. I've done this several times and while it's cheap and easy enough to do, it only gives fair results. The bores are not going to be perfectly round and may have some taper to them so use 'softer' cast iron rings that better seat themselves. Harder chrome rings are better for sealing perfectly machined bores. Again new rod and main bearings and valve seals are a good idea at this time. Another option is just replace the engine with a running engine from another truck or car. The '68-'72 510 uses the same L16 engine. 1 Quote Link to comment
G-Duax Posted March 20, 2018 Report Share Posted March 20, 2018 On my smoking, low compression on 2 cylinders, L18, I'm pretty sure I got into pre-ignition last summer, and broke a couple of compression rings, so you might luck out, and get by with just new rings, and a light hone job. I've had a couple of engines over the past 45 years, that when I popped a piston out of the bore, the rings were in little pieces. Quote Link to comment
racerx Posted March 20, 2018 Report Share Posted March 20, 2018 Who did the compression check? Did they do it right? Did they use the right tester? Better to use screw in type than plug in type. Quote Link to comment
Woc123 Posted March 20, 2018 Author Report Share Posted March 20, 2018 Thanks very much yes he used a screw in one. So it might go passed justbbeing the ring then it could also be more stuff messed up with it is getting the engine revuilt something expensive? Do you guys recomend anyone to rebuild the engine? Quote Link to comment
racerx Posted March 20, 2018 Report Share Posted March 20, 2018 How old is the engine? How many miles? Or find another engine and slap it in there. Quote Link to comment
datzenmike Posted March 21, 2018 Report Share Posted March 21, 2018 Thanks very much yes he used a screw in one. So it might go passed justbbeing the ring then it could also be more stuff messed up with it is getting the engine revuilt something expensive? Do you guys recomend anyone to rebuild the engine? What about... http://community.ratsun.net/user/468-hosestopmsncom/ ... he's a member here and has a shop in So Cal that does Datsun work. Surely he would know someone or have an idea? Quote Link to comment
wayno Posted March 21, 2018 Report Share Posted March 21, 2018 I would just buy a good used L20b, put the L16 oilpan on it and install that in your truck. 2 Quote Link to comment
Recommended Posts
Join the conversation
You can post now and register later. If you have an account, sign in now to post with your account.
Note: Your post will require moderator approval before it will be visible.