View Full Version : TR6 TR6 engine rebuild. Too tight?

04-27-2019, 02:56 PM
Is there a way to check if the engine is too tight. Honed the cylinders with a nice cross hatch, new rings also used a ceramic coat on the pistons for lubricity. Pistons went up and down nicely with out rings. Crank installed with standard thrust bearings. Crank turned nicely by hand and 6k on crank end play. So I installed the rings pistons and rods. The machinist that helped me checked the ring gap and said it was fine. It's been a long time since I did an engine rebuild but it seems like it's a bit too tight. Takes a bit of effort to turn and I can hear the rings scraping.

04-27-2019, 03:28 PM
I'm not aware of any accurate way to tell but normally you can turn it by hand with the flywheel without really straining. Some ring noise with the head off is not unusual.

04-27-2019, 06:42 PM
Mine was pretty stiff, and with the valve train installed, it was really hard to turn without some leverage. Started and ran fine, though.


04-27-2019, 06:51 PM
Back off all the piston and main bearing caps and give them a good rap with a rubber hammer in a circular motion. Now torque to specs and turn the crank as you go along. It should get tighter but now difficult. If you start with the mains, much better and just have the pistons loose. Bet it's much better than before.

STeve 1958
04-27-2019, 07:01 PM
When I rebuilt my GT6+ engine it was too tight to turn over with the starter. I had a neighbor pull me down the street to pop the clutch.
It fired right up and ran great without a tune up. After the oil got pumped around it always started like normal after that.
I think they will always feel tight until the oil gets in all the moving parts.


04-27-2019, 08:04 PM
I once had a problem with rings that were to small on the i.d.
Gaps were fine,skirt clearance ok but was tight after install.
I removed pistons and found that the ring gaps would not close on the piston,something no manual will tell you check.
If you used the old pistons and honed the cylinders skirt clearance should not be your issue although you should have measured to see if they were to loose.
I would pull out one piston and check.
You can also take the removed piston ,rod and ring assembly and install it with rod sticking out the head and use a scale,like a big fish scale and measure the pounds to pull it out.
I dont know the spec for your motor but someone may,I mostly do old mc motors.

04-27-2019, 09:53 PM
Ya my mechanic called me back tonight and said he used to leave just the oil scraper ring on and with some safety wire wrap around the the rod bearing hole and a fish scale (I'll have to re-calibrate mine to not inflate the weight) reinsert the piston and pull on the rod. Said it should be around 15 to 20 pounds.
I was thinking about installing the flywheel and starter to see how the motor will turn. But thinking about it without oil pressure I don't want to damage the bearings. Could install the pump, sump and plug all the oil ports to get some pressure. Might brake in the rings a bit and if it loosens up the engine a bit I feel a bit better about it. After what I just read though maybe my concerns are unwarranted.

04-27-2019, 10:20 PM
Didn't you use assembly lub when you put it together? That will stay on there for a while, so just checking it out should be no problem. Don't think I would use a starter except to see if it will turn over easy enough.

04-28-2019, 12:19 AM
yes and 50 weight oil.

04-28-2019, 08:54 AM
I dont understand your mechanics method.The oil ring has the least tension so why would you leave off the compression rings.Maybe I am misunderstanding but I think you are wanting to measure the drag of the complete asssemby of one piston and rings or the crank and all 4 pistons and all rings.
Easier if you dont want to take anything apart measure the torque required to turn over the assembley by turning with a torque wrench.
Maybe some other TR builders could give a reference.
I think you would be around 40 pounds or less ,which if I recall is about what a small block chevys range is.

04-28-2019, 09:08 AM
Since your crank turned easily...and assuming you can click the big end bearings back and forth to verify they are loose...you should be good. One thing...I use a lot more oil for assembly than you seem to have used. I douse the rings and pistons as they go together, and use enough in the bearings that I need a bucket under the motor until the oil pan goes on, or it will soak the workshop floor. You can never lube too much during assembly.

When torquing the flywheel bolts you should be able to spin the engine before reaching the bolt torques. Same for the big front bolt. If it doesn’t try to spin for those, then I would start to worry.

04-28-2019, 09:08 AM
I'm taking it all in and waiting for other replies. I know his biggest concerns are the oil rings.

04-28-2019, 10:03 AM
Did he say why he is concerned with the oil rings?
Are you using 3 piece oil rings?
I am also curious about the ceramic coating.Is this applied to the pistons by a company or something you applied?

04-28-2019, 10:25 AM
50 weight oil is way too thick for the rings and pistons and will contribute to the effort required to turn it over especially if your shop is cold. I use MM oil on the pistons/rings .

04-28-2019, 07:33 PM
I used CERAKOTE C-110. Applied it myself on the old pistons. Followed the directions and after 5 days you brandish the pistons with 00 steel wool which effectively takes off most of the coating and leaves you a remarkably smooth surface. Placed each piston in their respective holes to make sure they fit fine and there were no problems. Don't remember what the measurement were. The machinist did it too.

I did use OEM rings that have the 3 piece oil rings made by Hastings. He seems to be most concerned with the oil rings them the others. He knows an engineer at Total Seal Piston Rings and is always quoting him. Anyway he has built many engines and racing engines over the years and have a lots of faith in him.

04-29-2019, 06:08 PM
Did you use new pistons? if not, carbon in the grooves can foul up the fit. With used pistons, you can back-stroke with a hand held hack saw blade, followed by an old broken ring, to get the carbon out. On putting it together, I use lubriplate or STP on all journals and take the crank around one full turn after torquing each bearing. It doesn't look too late for you to take these steps. If you feel like it is too tight, don't risk not starting anew.

04-29-2019, 06:10 PM
And I use standard engine oil on the cylinders.

04-29-2019, 07:19 PM
I had them soaking in my parts washer for weeks. Then did what you suggested with a broken ring. Still on the stand with the cam. crank and pistons in. Probably no chance in starting for a couple or years. Still have to get the body off the frame and rebuild it. Then install the motor and trans. Probably try then to start.

05-01-2019, 07:57 PM
Took Toms (TSB) suggestion and put a torque wrench to it. Worked my way up from 10lbs. It clicked at 24 and turned at 25.

05-02-2019, 08:13 AM
Took Toms (TSB) suggestion and put a torque wrench to it. Worked my way up from 10lbs. It clicked at 24 and turned at 25.

Sounds completely normal to me...finish the build and tuck it away!

05-02-2019, 08:40 AM
I agree that sound like a reasonable number.
BTW you got me reading up on Cerakote.
HAve fun

05-03-2019, 12:31 AM
I'm beginning to think that too. I used Creakote on the tappets too and seem to spin much easier. Also in the timing cover where the chain tensioner rides.

05-03-2019, 10:37 AM
Just some background info:

The most common, and cheapest rings are straight cast iron. They do not have a perfect contact surface, so the cylinder bores must be prepped by honing to a relatively coarse cross hatch finish. This rough finish speeds lapping the face of the rings to achieve a perfect seal. Because of this, cast iron rings have a relatively long break in period...like several thousand miles. A side affect is the rough cross hatching increases the drag between pistons and cylinder. I bet these are the rings you used.

The next step up is moly faced rings. Molybedneum (spelling) rings are pre-lapped in a hardened steel cylinder during manufacture. Because the face is much better prepared, the cylinders should be honed to a mirror smooth finish. Moly rings will break in within a hundred miles of running...and if a break in procedure is used, they break in in a matter of minutes. The side affect of having rings and bores this smooth is there is little friction between the piston and cylinder...so the engine will easily spin by hand after assembly, compared to your build.

Then there are the specialty rings...chrome rings in iron bore, chromed bore with iron rings, nickel plated aluminum bore...and on and on. All the newer designers use a near mirror bore and pre-lapped rings to reduce break in and friction.

Anyway...most guys rebuilding our TR’s are still using the old school iron rings on a rough honed bore...so a lot of friction after the initial build is to be expected. The end result is just as good as modern engine builds, but you will have a longer break in time.

05-03-2019, 11:38 AM
One of the nicest features of the TR3 design is easily replaceable and relaltively inexpensive cylinders.I use only cast iron rings in my vintage bike motors but cylinders are rare,softer cast iron than modern bores and I would rather have the rings wear ,not the cylinders.They are also more forgiving to a not perfectly round bore.Burnishing the final 220 grit hone with a few qiuck passes by hand of some 400 or a burnishing brush nocks the peaks down but like John mentioned longer break in is required .
The only problem I have ever heard of with the three piece oil rings was incorrect install with the spring spacer not set right.
Im always amazed when top fuel dragster guys replace pistons and rings and blast a full out run.They have pistons with gas ports to pressurize the rings.
Someday I may find out whats in my TR3 as the short block came to me rebuilt.12k now,hopefully good for another 100k.
Arnt these just the coolests motors!