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521 cid broken camshaft dowel for timing gear . bent valves

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Lem Evans
rmcomprandy
lance flake
norm
Dave De
supervel45
maverick172
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Post  maverick172 May 13th 2023, 11:01 pm

so been running my new build for about a month and 4th pass today the dowel let loose on the timing gear on camshaft sheared off . bent all my exhaust valves bent 1 intake valve and banged up the pistons . i think pistons are ok what you guys think i will post a couple pics . these were sr-71 heads on a 4.39 bore and i have a feeling the vales got close to the bore edge as i see nicks in each cylinder edge . what you guys think i will post pics of couple bore edges . these heads are suppose to be fine on a 4.39 bore with small exhaust valve 1.70 exhaust 2.370 intake when i assembled this engine i check all my clearances from top of piston to valve but i never check bore side clearance ? did not know i had to check side clearance ? the cam only had 1 dowel do i need to double dowel this? what you think anyone could chime in thanks521 cid  broken camshaft dowel for timing gear . bent valves Img_0014
521 cid  broken camshaft dowel for timing gear . bent valves Img_0013
521 cid  broken camshaft dowel for timing gear . bent valves Img_0015

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Post  supervel45 May 14th 2023, 1:47 am

I would double pin the camshaft. I would also inspect my exhaust valve guides after that for potential wear/damage. If the fix turns out to be to notch the block and I was running a fire ring head gasket, I would pay close attention to it in the area of the notch.

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Post  Dave De May 14th 2023, 6:56 am

I would be concerned about a pinched ring land. If you stay with a single pin use a case hardened alloy steel pin. Drill and tap the 3/8" hole to 7/16-20 and use an SBC crankshaft end bolt with higher torque according to the size.
Dave De
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Post  maverick172 May 14th 2023, 7:52 am

supervel45 wrote:I would double pin the camshaft. I would also inspect my exhaust valve guides after that for potential wear/damage. If the fix turns out to be to notch the block and I was running a fire ring head gasket, I would pay close attention to it in the area of the notch.
ya my plan is double pinning camshaft . i am also running a 7/16 cambolt. i inpsected the washer on the bolt as well it is thick and did not appear to be mushroomed i wonder if i should shave 4 or 5 thou off the end the camshaft to allow the camshaft to be extra>" lower than the cam sprocket . i def will not be running this cam spocket agin as i see the first 1/4 of it has a bigger hole the rest the sprocket.
ya i am going to mock it up on my other 4.39 bore block and see if the valve is to close to "kissing the side the block as i think could be possible culprit as well.

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Post  maverick172 May 14th 2023, 7:57 am

Dave De wrote:I would be concerned about a pinched ring land. If you stay with a single pin use a case hardened alloy steel pin. Drill and tap the 3/8" hole to 7/16-20 and use an SBC crankshaft end bolt with higher torque according to the size.
ohh i did not think about a pinched ring land but that could be possible as well. 930245690 is the pistons i am running they have a fair bit of "meat" before the top ring starts but yes could of bent a ring land anyone else care to chime in would rather not pull the rest the engine and tear it down if i dont have too. but..

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Post  supervel45 May 14th 2023, 8:24 am

Dave has a very good point about checking the ring lands. They got hit on the edge of the pistons pretty good, it looks like. It would really suck to put it back together and find out then! Also mocking it up on a block that it is not going on does not insure that the dowel pins are in the exact same spot or that it was bored exactly the same. Also Randy mentioned offset dowel pins when the SR-71's first came out due to the fire ring issue on the small bores. I don't know if that may have any use here but, maybe worth checking into. Don't know what to tell you on shaving the cam either, did not quite understand the question either on the reasoning.

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Post  maverick172 May 14th 2023, 8:36 am

supervel45 wrote:Dave has a very good point about checking the ring lands. They got hit on the edge of the pistons pretty good, it looks like. It would really suck to put it back together and find out then! Also mocking it up on a block that it is not going on does not insure that the dowel pins are in the exact same spot or that it was bored exactly the same. Also Randy mentioned offset dowel pins when the SR-71's first came out due to the fire ring issue on the small bores. I don't know if that may have any use here but, maybe worth checking into. Don't know what to tell you on shaving the cam either, did not quite understand the question either on the reasoning.

ya i probably going to pull the block out now and put on engine stand
but my idea with "shaveing the end the cam down was to create more space between the "face" cam gear and the end the camshaft to create more space in between the camshaft end measure 7.890 and the cam sprocket thickness measure 7.900 so there is a 10 thou gap" if you want to call it between my washer measures 1 1/8 around i wonder if it did not create enough of a clamp and i should go to a 1 1/4 washer size washer is 3/16 thick and i think thickness is fine but diameter might be small?

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Post  supervel45 May 14th 2023, 9:00 am

The timing gear failure may have bent the valves enough to contact the block as the crank was still going around and the cam still turning.

When the pin sheered, the bolt may have held it, just long enough to keep the cam turning, and not go fully out of cam timing instantly, until it lost all compression. Hence the nick on all cylinders. Or something like that.

It would seem you would have felt that much interference contact while lashing your valves.

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Post  maverick172 May 14th 2023, 9:06 am

supervel45 wrote:The timing gear failure may have bent the valves enough to contact the block as the crank was still going around and the cam still turning.

When the pin sheered, the bolt may have held it, just long enough to keep the cam turning, and not go fully out of cam timing instantly, until it lost all compression. Hence the nick on all cylinders. Or something like that.

It would seem you would have felt that much interference contact while lashing your valves.

well to be honest i lashed all the valves before going out and i noticed there was a couple out about 2-3 thou

ya you could be correct on the valves moved enough while still bent to nick the cylinders .

what size is the cam washer you run seems my camshaft washer may have been to small diameter . after reading some guys running up to a 2inch diameter washer

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Post  supervel45 May 14th 2023, 9:32 am

maverick172 wrote:
supervel45 wrote:Dave has a very good point about checking the ring lands. They got hit on the edge of the pistons pretty good, it looks like. It would really suck to put it back together and find out then! Also mocking it up on a block that it is not going on does not insure that the dowel pins are in the exact same spot or that it was bored exactly the same. Also Randy mentioned offset dowel pins when the SR-71's first came out due to the fire ring issue on the small bores. I don't know if that may have any use here but, maybe worth checking into. Don't know what to tell you on shaving the cam either, did not quite understand the question either on the reasoning.

ya i probably going to pull the block out now and put on engine stand
but my idea with "shaveing the end the cam down was to create more space between the "face" cam gear and the end the camshaft to create more space in between the camshaft end measure 7.890 and the cam sprocket thickness measure 7.900 so there is a 10 thou gap" if you want to call it between my washer measures 1 1/8 around i wonder if it did not create enough of a clamp and i should go to a 1 1/4 washer size  washer is 3/16 thick and i think thickness is fine but diameter might be small?

I measured one of my CompCams timing gears and the pin hole is oversize for .195" on the back side. The mark from the factory washer that was on it is 2.35" or so.< Edit that, that was the fuel pump ecentric wear mark. I have always used the stock washer, what ever size they are.
The cam snout measured .796 to .798 on one of my cams. With the cam gear all the way down on the Lunati Cam, I get about .088" to the front face of the gear from the snout of the cam.

Since you are double pinning the cam and replacing the gear, I would send it all to Lem if he still does them and let him set it all up. If not make sure your machinist is up on his Ford game.


Last edited by supervel45 on May 14th 2023, 10:05 am; edited 1 time in total

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Post  norm May 14th 2023, 9:57 am

Make sure the timing gear bolt isn't too long bottoming out in cam, not allowing it to be actually tight clamping the gear to the cam.

Cam might not be tapped deeply enough too.
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Post  maverick172 May 14th 2023, 10:09 am

so looks like you have close to 100 thou differance from cam snout length to cam width . which makes sense to me as it would create clamp force mine is way tighter only 10 thou .
not sure what you were referring to on the pin hole size remark if you could clarify ?so you washer diameter was 2.35 that is a huge washer ?
supervel45 wrote:
maverick172 wrote:
supervel45 wrote:Dave has a very good point about checking the ring lands. They got hit on the edge of the pistons pretty good, it looks like. It would really suck to put it back together and find out then! Also mocking it up on a block that it is not going on does not insure that the dowel pins are in the exact same spot or that it was bored exactly the same. Also Randy mentioned offset dowel pins when the SR-71's first came out due to the fire ring issue on the small bores. I don't know if that may have any use here but, maybe worth checking into. Don't know what to tell you on shaving the cam either, did not quite understand the question either on the reasoning.

ya i probably going to pull the block out now and put on engine stand
but my idea with "shaveing the end the cam down was to create more space between the "face" cam gear and the end the camshaft to create more space in between the camshaft end measure 7.890 and the cam sprocket thickness measure 7.900 so there is a 10 thou gap" if you want to call it between my washer measures 1 1/8 around i wonder if it did not create enough of a clamp and i should go to a 1 1/4 washer size  washer is 3/16 thick and i think thickness is fine but diameter might be small?

I measured one of my CompCams timing gears and the pin hole is oversize for .195" on the back side. The mark from the factory washer that was on it is 2.35" or so.< Edit that, that was the fuel pump ecentric wear mark. I have always used the stock washer, what ever size they are.
The cam snout measured .796 to .798 on one of my cams. With the cam gear all the way down on the Lunati Cam, I get about .088" to the front face of the gear from the snout of the cam.

Since you are double pinning the cam and replacing the gear, I would send it all to Lem if he still does them and let him set it all up. If not make sure your machinist is up on his Ford game.

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Post  supervel45 May 14th 2023, 11:14 am

The pin hole on the cam gear is bigger, than the dowl pin on the cam, for almost .2" before it reduces, to the proper diameter. I edited my earlier post, that was the wear mark was from the fuel pump eccentric. I just used a stock Ford washer what ever size they are. I would think if the cam snout is not sticking out past the gear, you should be OK. .010" is pretty close though. A larger washer should always have more bite because it has more surface area to grab, all thing being equal.

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Post  supervel45 May 14th 2023, 11:19 am

norm wrote:Make sure the timing gear bolt isn't too long bottoming out in cam, not allowing it to be actually tight clamping the gear to the cam.

Cam might not be tapped deeply enough too.

Especially without a fuel pump eccentric.

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Post  lance flake May 14th 2023, 4:40 pm

The pin will break when the bolt gets loose or doesn’t have enough clamp force. The pin is only for location. I usually double pin them. This sometimes will keep from getting the cam bad out of time. Seems that it will break a single pin and bend them when doubled.

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Post  rmcomprandy May 14th 2023, 6:03 pm

lance flake wrote:The pin will break when the bolt gets loose or doesn’t have enough clamp force. The pin is only for location. I usually double pin them. This sometimes will keep from getting the cam bad out of time. Seems that it will break a single pin and bend them when doubled.

YEP, the pin(s) are supposed to be for locating the valve timing ... I use a hardened ARP washer with a 7/16-20 rod bolt to get 80 lb/ft of tprque on the bolt; the clamping force is supposed to keep the gear from rotating ... not the pins.
Of course one must be careful that the bolt is not bottoming in the hole.

I have NEVER had a broken pin issue doing it this way ... with over a 1,000 lbs of spring force a lot of times.
.

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Post  maverick172 May 14th 2023, 6:08 pm

rmcomprandy wrote:
lance flake wrote:The pin will break when the bolt gets loose or doesn’t have enough clamp force. The pin is only for location. I usually double pin them. This sometimes will keep from getting the cam bad out of time. Seems that it will break a single pin and bend them when doubled.

YEP, the pin(s) are supposed to be for locating the valve timing ... I use a hardened ARP washer with a 7/16-20 rod bolt to get 80 lb/ft of tprque on the bolt; the clamping force is supposed to keep the gear from rotating ... not the pins.
Of course one must be careful that the bolt is not bottoming in the hole.

I have NEVER had a broken pin issue doing it this way ... with over a 1,000 lbs of spring force a lot of times.
.
one more question on ring land pinching . i was going to pull bottom end out and tear it down looking for pinched ring lands on the piston but i can clearly easily rock the pistons side to side and 90 degree side to side and see the ring moving freely in the piston . shoul di worry about this or just run it this way ?also the marks on the pistons shoudl i file them off?

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Post  Lem Evans May 14th 2023, 7:15 pm

Valve clipping the bore what broke the pin??

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Post  maverick172 May 14th 2023, 7:21 pm

Lem Evans wrote:Valve clipping the bore what broke the pin??
seems as though too small of cam retainer washer

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Post  lance flake May 14th 2023, 10:14 pm

Lem Evans wrote:Valve clipping the bore what broke the pin??

I think you are correct the vibration through the valve train most likely the issue. Randy is correct about the bolt bottoming out. I had this happen a couple times in my earlier years when I was a lot smarter than now.

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Post  rmcomprandy May 14th 2023, 10:45 pm

Lem Evans wrote:Valve clipping the bore what broke the pin??

The photos of the top of the cylinder make it look as though that might have been the case.

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Post  maverick172 May 14th 2023, 11:17 pm

well i am going to pull bottom end apart and mock the head on with no pistons and verify . the one clearance i did not check as they work on the 4.39
rmcomprandy wrote:
Lem Evans wrote:Valve clipping the bore what broke the pin??

The photos of the top of the cylinder make it look as though that might have been the case.

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Post  Mark Miller May 14th 2023, 11:35 pm

rmcomprandy wrote:
lance flake wrote:The pin will break when the bolt gets loose or doesn’t have enough clamp force. The pin is only for location. I usually double pin them. This sometimes will keep from getting the cam bad out of time. Seems that it will break a single pin and bend them when doubled.

YEP, the pin(s) are supposed to be for locating the valve timing ... I use a hardened ARP washer with a 7/16-20 rod bolt to get 80 lb/ft of tprque on the bolt; the clamping force is supposed to keep the gear from rotating ... not the pins.
Of course one must be careful that the bolt is not bottoming in the hole.

I have NEVER had a broken pin issue doing it this way ... with over a 1,000 lbs of spring force a lot of times.
.

So you don't use double pins it doesn't sound like you do just making sure?

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Post  Mark Miller May 14th 2023, 11:38 pm

Lem Evans wrote:Valve clipping the bore what broke the pin??

Sure looks like the valve clipped the bore!!

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Post  supervel45 May 15th 2023, 4:50 am

Maverick did you ever put a caliper on those exhaust valves and verify they are 1.70"?


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