• Hi Guest!
    You can help ensure that British Car Forum (BCF) continues to provide a great place to engage in the British car hobby! If you find BCF a beneficial community, please consider supporting our efforts with a subscription.
    There are some perks with a member upgrade!
    **Upgrade Now**
    (PS: Subscribers don't see this gawd-aweful banner
Tips
Tips

TR5/TR250 Compression #

Share this page

tinman58

tinman58

Jedi Knight
Country flag
Offline
We now have about 650 moiled on the 250. We just drove to the Tibuorn show on Saturday. 160 miles round trip. The motor runs smooth but I feel that there is excess oil consumption. A good 1/2 quart in that 160 miles. I have 1 small oil leak at the front timing chain cover. (the size of a quarter). The plugs are a little black, running a little rich.
I checked the compression on each cylinder and came up with these numbers.
1- 137
2- 142
3- 140
4- 144
5- 145
6- 145
The motor is a 1972 model TR6. The compression was raised to 9.5 to 1, I don't know if these numbers are low, high or what. I can't find anything on the compression lbs. How long will it take for the oil rings to seat? Or am I just being a little pearinoid?
 
tinman58 said:
...How long will it take for the oil rings to seat? Or am I just being a little pearinoid?
Click to expand...

Possibly -- what break-in procedure did you follow?

Unless shockingly low I usually regard the usefulness of compression numbers to be comparative from one cylinder to the others rather a meaningful absolute value. For one thing, some gauges are not particularly accurate (though they usually yield repeatable results).
 
Once you go thru the compression test with 'dry' cylinders, then right away do it again adding 2 tablespoon equivalents of motor oil to each cylinder as you get to it you'll get an idea about the rings sealing.
 
Dan on my rebuild I got about 160-165 in each, also going to a 9.5/1 ratio with a milled head. That said as noted the gauge might be off.
 
I did the 20 minute break in for the cam and lifters. I also used break in oil for the first 500 miles. Changed the oil and used valvoline 20-50 oil in it now. During the first 500 miles I just drove it normally, but never got close to red line 3800 rpm's max. I did not baby it but did not abuse it at all.
 
tinman58 said:
...During the first 500 miles I just drove it normally, but never got close to red line 3800 rpm's max. I did not baby it but did not abuse it at all.
Click to expand...

I prefer to break-in new rings with something closer to abuse... hard acceleration followed by abrupt deceleration. Rinse, repeat.

I try to avoid driving at a steady RPM (like one might normally drive). You do not want to lug the engine at low RPMs, but IMO high RPMs and abrupt change are needed to seat the rings.

I once had an engine that the PO had replaced the rings and, I suspect, never got them to seat. The procedure described above didn't help and in the end I did the thing with a dose of Bon Ami in the intake. It isn't an abrasive but rather absorbs the oil from the cylinder walls so you get a couple of dry strokes before lubrication resumes. That seemed to do the trick.
 
Are you using oil with ZDDP? Valvoline 20-50 may not have enough for your flat tappet lifters and cam. You'll wipe it out quickly without added ZDDP of oil such as Brad Penn which has the required levels of ZDDP.
 
A really bad thought. We rebuilt 3 engines, all with parts from a major supplier. Two of the engines had oil rings that were 3 parts. Top and bottom scraper, and a tension ring in between. The tension rings broke the ends off on two of the engines and they ate some much oil (pushed up the cylinder walls) that we had to pull the pistons out the bottom and replaced the oil rings. That cured the problem. The third engine had parts from the same supplier but the oil rings were different. No problems burning oil with that engine.

Our replacement rings were from Hastings. You can look the rings up on their web site and see if yours look like that.
Jerry
 
I have added the zddp with the break in and with the valovline. Jerry I got the pistons and rings from british parts northwest. I think. I will just keep driving. Recheck compression in another 500 miles.
 
Geo Hahn said:
with a dose of Bon Ami in the intake. It isn't an abrasive
Click to expand...
Just want to point out: There are two different Bon Ami powders and one of them does have the hard abrasives in it that can scratch cylinder walls and so on. If you are going to do this, be sure to hunt for the one that says it is safe to use on glass.

When I went looking, none of the local grocery stores had the "safe for glass" variety; but I found it at OSH.

Running rich can be really bad on new rings, especially if you are running fuel with ethanol added.

Based on my own (limited) experience, I'd say a pint in 160 miles cannot be adequately explained by rings that have not "seated". They should do better than that even right out of the box! One experiment I would try first is to have someone follow you, and look to see whether the blue smoke is worse when you get on the throttle; or if you get a big puff of blue when shifting. The latter indicates oil getting past the intake guides rather than the rings.

After that, I'd be pulling a piston to see WTF.

PS, Here's a write-up on the two different versions of Bon Ami. Apparently, they have changed the labels yet again.
https://www.bonami.com/index.php/products/powder_cleanser/
 
Back
Top