Massive sound after Rebuild.. What went wrong?!

[SprintStar]

Hello All,

I just put together a '77 3.0 Turbo engine.

Ps & Cs have been upgraded to 98mm, giving 3.2 displacement. The pistons are 8.5 CR JEs whereas the cylinders are freshly replated Nikasils.

Cams are SC cams timed to 1.0mm valve lift at TDC with 0.1mm valve clearance. I know the Bruce Anderson book says to time them at 1.55mm but I was thinking that since I have got 8.5 CR, giving me good low end, I can retard the timing to gain power on the top end.

Started the engine and it runs with a rattle. Good oil pressure though. I cannot really tell if the rattle is a mechanical noise or a combustion or exhaust leak.

Pulled the plug leads out one by one. All except number 4 slowed down. Cylinder 4 showed no difference.

Pulled the plugs and 4 was wet with petrol. I blew at the plug and got some gas on my face!

Ran compression check. ZERO compression on cylinder 4.

I don't think the valves are binding. I removed the valve covers and the rockers moved up and down while a friend cranked the starter.

I also noticed some metal shavings on the the plug.

What went wrong? Bad cam timing? Too high CR? The rattle happened each time TDC occurs, not once every 2 cycles as it would if it was a particular cylinder at fault. Is it something in the crankcase? What can cause the sound?

I'm lost. Please help.

Sprint.

[Jeff Alton]

Did you do a valve to piston clearace check when you assembled the motor?

Jeff

[Grady Clay]

My guess is a combination of cam timing and piston configuration that has the valves hitting the pistons. The #4 was at the limit and bent a valve but I’ll speculate all the valves are contacting the pistons. What is the cylinder leak test measurements? Is #4 all past the intake valve?

Please report back what you find.

Best,
Grady

[tsuter]

Originally posted by SprintStar

Ran compression check. ZERO compression on cylinder 4.

Simple....zero compression means you have a big hole. Not likely a blown cylinder or rings either since you just put it back together and even a blown or missing ring gives some compression so its your valves.

[SprintStar]

Originally posted by catca
Did you do a valve to piston clearace check when you assembled the motor?

Jeff

I'll admit. I didn't do that. Reason was because it's not a high lift cam (SC) and while the CR was higher than stock at 8.5, it's way below what the SCs run which is about 9.5 to 10.3?

Sprint.

[Wayne 962]

Originally posted by SprintStar
I'll admit. I didn't do that. Reason was because it's not a high lift cam (SC) and while the CR was higher than stock at 8.5, it's way below what the SCs run which is about 9.5 to 10.3?

Sprint.

Doesn't matter. When you machine the parts, they all change clearances. A piston / valve clearance check is arguably the most important check in assembling the engine.

The valves are probably bent - if they are not closing all the way, then your valve clearances will be way off. Measure the valve clearances, and let us know what you find.

Do you have a copy of the Engine Rebuild Book?

-Wayne

[MotoSook]

Did you spin the engine while it was on the stand?

[randywebb]

It sounds like the big hole might be a bent valve...

The question is what to do now. Maybe there is a safe alt. to a top end tear down. I dunno if there is - others might know of one.

Be sure to save all the oil when you drain it to strain; and to open up the filter and look for metal pieces. You can do that w/o pulling the engine out.

[Eagledriver]

You could check your valve to piston clearance now on one of the other cylinders to see if it's too close. That would tell you if the pistons have hit the valves. Because you ran the cam retarded you will find that the exhaust valve is closer to the piston as the piston chases the valve on it's way to TDC than it would be with normal timing. To check the clearance do the following:

1. Turn the motor to about 5 degrees BTDC on an overlap cycle (the same way you set the cam timing but with the crank 5 degrees BTDC).

2. Turn the adjuster screw on the rocker arm in until the exhaust valve hits the piston. If you get less than a full turn (1mm) you probably hit the pistons to the exhaust valve.

My estimate of using 5 degrees BTDC is based on measurments I did on my engine and may not be the closest point but it should get you in the ball park. Note that most people do this measurment at TDC and that will not give an accurate measurment. The piston moves very little during that last 5 degrees whereas the valve moves more.

1mm is not really enough clearance but it should be enough to establish that you didn't hit the valves. If you retimed the cams you could get about .5mm more and that would be enough.

-Andy

[axvel]

Well, i just took a 3.2 appart due to a rattling noise, and found out that piston #4 had destroyed the bearring making it loose. The Bearing that goes between the piston and crank to make it tight. see pics belowe



On This one you can see the edge of the pictons conector being scraped.



On This one you can see the difference between pistons, the one on the right is a good one with the shiny sides and bearing, and the one on the left shows that this bearing was eaten alive, i found bits and pieces of it once i opened the case.









Well hope this helps, please excuse me if i got the names of parts wrong.

[Blanco]

Interesting...

Would lack of lubrication cause that?

[Dixie]

WHAT bearing? I do not see a bearing on the one rod. Did it get left out?

[Rex Walter]

SprintStar,

I just went through the piston to valve clearance check after my rebuild, and I failed the check. I had a stock 2.7L with the stock 8.5:1 pistons and an SC profile cam. What could possibly go wrong? The cam timing was suggested at 1.4 to 1.7 mm. I initially set the cam timing to 1.6mm and found the my intake valve would hit at about 0.75mm of lift at about 15 deg ATDC. I retimed to 1.5mm of lift and found that my interference had improved to just over 1.5 mm (Maybe timing of 1.55mm is the right position). Eagledriver has a good idea to do the check now with the engine in the car. Wayne's book describes a method where the intake and exhaust valves are openned 1.5mm and 2.0mm respectively, and the engine is turned over slowly by hand to see if there is any interference. (The interference will occur somewhere near TDC). Hope this helps.

Rex

[JeremyD]

Ouch! Yes, where is the rest of the bearing? Did you use assembly lube? Wow - Hope you didn't bend anything!

[Wayne 962]

Get one of the Engine Rebuild Books please:

http://www.101projects.com

-Wayne