It that the 420a or 4g63? If its the 420a expect the worst possible (bend valves) honestly at 75mph on any motor that the timing belt breaks would be disasterous. Man sorry bout your luck there. I would pull th head if it was mine n see what kind of damage was done. If your one of the very lucky few n just replace the belt n tensioner

6 bolt n/a would imply the 1g 4g63 n/a? Correct me if im wrong. I know for sure the 4g63 is an interference motor. Expect many many bent valves. The 420a? Most likely interference, so expect the same.

Line up all the marks if you want to prove whats what without taking things apart. Then do a leakdown test. Then you wont be too shocked when you pull the head

4g63. While I was taking out the tow rope my grandpa turned the cam gears with a pipe wrench, Smh. His reply was the valves were still good.

The 420a is an interference motor as well. Thats what im running. He would need to replace the belt to do the leak down test.

I was able to turn my motor via the starter or with a wrench. The valves were still totalled

99% of the time with these motors if the timing belt goes so do the valves. N hopefuly they didnt score your pistons heads up as well

Yea, I'm sure my head is toast I just wanted post.

Your head is still fine. Just gotta rebuild it. Its probly cheaper for you to rebuild it then to find a new one. If you have any mechanic experence.

At 75... it could have pounded the pistons as well. You never know though. Just have to tear it apart.

You can do a leakdown by putting(geeeeeentlyyyy) #1 at TDC and lining up the cams. I would first put a long screw driver down the #1 well(or any for that matter) and when its roughly half way down, THEN line up your cam marks. Rotate #1 to TDC and do your leakdown. I dont think you even need to waste time with it, but it is possible. I would just go ahead and pull the head or the whole motor

I agree with boost97 pull the head. Im certain u did damage n its gonna have to come off to fix it

Thanks guys

I recently was between 60-65 mph on a 420a when the timing tension er gave out, that resulted in bending 2 valves.

Not sure why all the 420a talk came up but the result will have been the same. Expect all/most of the valves to be bent. I have seen the valves put holes in piston tops and valves break causing havoc on the CC and make a head "unusable" for the most part. If it were me I would be a complete tear-down to at least check some things:

Valves (they will need replacement)
Valve guides (cracks or scoring from bent stems)
Valve seat damage (rare but it could happen)
Rockers (for cracks/breakage/bearing damage)
Lifters (very possible to blow a lifter seal when the valve is forced closed)
Camshaft Journals (I wouldn't worry about this unless you see a bad rocker)
Camshaft bearing surfaces (for scratches/scoring)
Piston top (for holes/cracks)
Wrist pin (scoring/cracks/breakage) This is unlikely but it's still something I would check
Rods (bending) Also unlikely
and the best for last...
Rod bearings, most people don't even bother to look at the bottom end when timing related damage occurs however the bearing is soft and takes quite a pounding in the event of valve-piston contact. It would suck to put everything together and have rod knock 30 miles down the road (ask me how I know).

There are probably other things you'd want to check while things are apart but those are what I feel to be the most imperative.

phr0st said:

Not sure why all the 420a talk came up but the result will have been the same. Expect all/most of the valves to be bent. I have seen the valves put holes in piston tops and valves break causing havoc on the CC and make a head "unusable" for the most part. If it were me I would be a complete tear-down to at least check some things:

Valves (they will need replacement)
Valve guides (cracks or scoring from bent stems)
Valve seat damage (rare but it could happen)
Rockers (for cracks/breakage/bearing damage)
Lifters (very possible to blow a lifter seal when the valve is forced closed)
Camshaft Journals (I wouldn't worry about this unless you see a bad rocker)
Camshaft bearing surfaces (for scratches/scoring)
Piston top (for holes/cracks)
Wrist pin (scoring/cracks/breakage) This is unlikely but it's still something I would check
Rods (bending) Also unlikely
and the best for last...
Rod bearings, most people don't even bother to look at the bottom end when timing related damage occurs however the bearing is soft and takes quite a pounding in the event of valve-piston contact. It would suck to put everything together and have rod knock 30 miles down the road (ask me how I know).

There are probably other things you'd want to check while things are apart but those are what I feel to be the most imperative.

Click to expand...

Good answer! Everything this guy said, OP, check it all. Dont want to get bit after all that work. It sucks(ask me how I know as well ha)

I notice you said you did a "budget build" did this shop re-use an old timing belt / tensioner?

Remanufactured heads can be had for less than $500.

It the pistons are dinged make sure it didn't get close to the cylinder walls. Also make sure if you are going to reuse the pistons that you deburr any of the dents put in by the valves.