Topic: Engine teardown diagnosis, need input

[garretcb750]

 I've been really hoping to build a big bore motor this winter but realistically I can't do it... I'm half way through a VW beetle/dunebuggy build and I would like to finish that.

However.... I already have a webcam grind 41, a low mile K7 or 8 motor and gasket kit. I also have a few other motors. a disassembled F2, a seized F1, 750A, and 2 early 70 motors. I wanted to use the K8 motor because I'm concered about how functional the bottom ends are in the others and I figure the K8 has most likely seen the less abuse. I think the motor in my F is becoming alittle tired and it seems to be slipping out of gear now and then. When its cold the cam or Pri chain makes quite the racket. So... maybe a fresh topend rebuild and a cam would suit me for now. It would be nice to leave my current motor to the side.... Just in case...hah.

By rebuild... I mean replace the rings if needed, clean and inspect the head, seat the valves and install the webcam. I will use the F2 charging rotor because its lighter. If money permints in the spring I'll buy a set or 29mm CR carbs.

Now for my questions... Webcam says the grind 41 "bolts in" to stock engines... does this mean I'll still need an adjustable cam sprocket? On the timing card it says if you have a "bolt in" cam you can skip steps 1 through 5 on there setup card.

Also... I know the 77/78 F heads have there problems and most builders prefer the 75/76F heads or early K's. But what about the 77/78K?Should I use a cylinder head off one ot the earlier K motors I have.

[Old Scrambler]

I'd stay with the 77-78 K head and the fixed cam sprocket unless you plan on a highly competitive racer. Since you already have a late F motor, just put that cam in the K motor.  It has longer duration and is REALLY a drop-in application with no required timing mods.

[garretcb750]

ohh sorry.. my F is a 75.

[garretcb750]

I just want alittle more punch for daily use... I have a Dyna S ignition, oil cooler and header already. I'm also running jetted carbs with velocity stacks.

[BLUE71TURBO]

So what are ya gonna do with the rajay turbo ?   

[Inigo Montoya]

I always thought that the sought out engines were the 77/78 K engines. Better oiling and compression stock along with a better clutch and all the improvements made to the engines over the years.

[garretcb750]

HA.. the rajay is for my 500, the 750 is my daily driver.

[754]

Inigo, what do you mean by better oiling? I dont think the K has higher compression.

 Re 750 F late cams vs the 41 dropin or similar;

 Does the 41 produce a bit more power or rpm? just thinking that the F being stock, is a bit constrained to keep within emissions, than any aftermarket (offroad) cam..

[Inigo Montoya]

Not that it amounts to much but the 77/78K had 9.2:1, the earlier years were 9:1.
Also, from what I read in other posts from mreick is that there were additional oil galleys in the head I think.
I stumbled across the post but did not mark it.

[garretcb750]

found this on an old post..

The F-2 cam has the 'broken band' cast in.
F-2 cam specs (as measured), it supports the service manual says:
Lift: Int. .318", exh. .302"
Duration: 225 deg @ .040" lift
Overlap: 10 deg @ .040" lift
Lobe Centers: 107.5


My Webcam is the smallest they offer at 360 lift with 270 duration.  seems alittle bigger than those numbers.

[NitroHunter]

For emission purposes, almost every later years engines duration and consequently, valve overlap, was reduced. This was done by opening the lobe centers into the 108 area as compared to 104-105 for most early hotrod grinds. In general, more overlap = higher rpm breathing efficiency.
I would, without hesitation, opt for the 41. The F-2 is NOT a performance cam.

[garretcb750]

ok... People keep referring the 41 to a close to stock cam. SO.. it is a better cam than a stock F2 and much better than a K cam? good to know. I got a good deal on it on ebay so why not throw it in. Anyone one else see a problem with me just bolting it to a stock cam sprocket? should be ok?

[MCRider]

ok... People keep referring the 41 to a close to stock cam. SO.. it is a better cam than a stock F2 and much better than a K cam? good to know. I got a good deal on it on ebay so why not throw it in. Anyone one else see a problem with me just bolting it to a stock cam sprocket? should be ok?

Should be fine, might need to tweak the jetting. I'm curious to hear about it. I have that cam for my project, but its an 888cc, so not apples to apples.

[voxonda]

Now we're on the subject, would a 41a work in a F2 head? Duration is 10° longer than the 41. Or will I encounter problems with the valves?

Thanks, Rob

[garretcb750]

I thought dynoman recommended the 41a grind for F2's

[voxonda]

I thought dynoman recommended the 41a grind for F2's

According to his site that would be the 41 grind.

[garretcb750]

Ok... So I removed the engine today from the 77 K and got it on the engine stand. I did a cold compression test and found approx 120 psi across all for cylinders.

Once I removed the valve cover I realized there were issues. Number one cam cap was dark, once I removered the cap it wasn't hard to tell the cam and holders were SHOT!. Both ends of the cam were really chewed up, aswell as the cam holder assemblies. The 2 inward bearing surfaces were good. There was some heavy sludge build up between the first and second cam caps. Was all this damage most likely caused by oil starvation? and Are F2 cam holder assemblies the same as previous years?

The pistons looked ok, and there doesn't seem to be much scoring on the sleeves. I took a few pictures to post.

[garretcb750]

Here are some pics of the damage and let me know if you think the pistons should be changed.




There was alot of sludge in the top end.. grease like.



I found some flakes of what seems to be gasket material, or thick paper. What could it be?

[garretcb750]

Should this motor be completly tore down to find out the cause of the damaged cam?

[bwaller]

Should this motor be completly tore down to find out the cause of the damaged cam?

Absolutely to clean all the crap out of the engine. Check to see if the oil restrictor is blocked on that side. 

[garretcb750]

were is that? what am I going to be looking for when spliting the cases. Is it necessary to remove the trans aswell or do I just want to check the crank and rods?

[bwaller]

The early heads had the restriction cast into the head, but later years use a "jet like" restrictor in the oil feed passage under the cam tower. There is an o-ring around it to seal and can be wiggled out of its seat in the head.

By the looks of the pan I would absolutely dismantle the engine completely to clean well. Splitting the cases isn't difficult just have plenty of space available to place all the parts. Once the cases are apart you'll see better how easy the job will be. This will also be the time to change seals, camchain, primary chains and check for any other potential issues while it's apart.

You're in the right place for help.

[garretcb750]

Trans should be ok right? does any part of the trans get lube through a passage or from the pump? I've dismantled my F2 motor before. Fairly easy. But I will deffinatly need some help the first time around.

[garretcb750]

Since I have multiple motors, Would I be better off mixing qualities I would like to have, ex.. The F2 trans is a closer ratio, right? it would be better for around town driving... this is what I do most. I would like the earlier out put shaft. I'm running a 530 chain on my bike. I find the 630 way too heavy. the K7 pistons and ring gap are within spec. be nice to have that 9.2:1 rather than 9:1 compression.

Or am I asking for trouble mixing parts from motor to motor. Maybe I should be using an earlier crankcase with the K7 topend I just removed and replacing the cam holder/rocker ass.

I will completly go through which ever crankcase I use and clean everything.. its only proper.